SILT BARRIER

Field of the Invention

The present invention relates to a silt barrier and especially, but not exclusively, to a silt barrier for preventing or reducing loss of particulate material such as silt, including top soil, from a construction site.

Background of the Invention

Silt barriers are used in various applications, to reduce loss of topsoil, and are often used on construction sites .

Loss of top soil from construction sites, due to the top soil being washed from the site by rainwater or the like is a common problem and is undesirable because it can lead to erosion of the site and large amounts of top soil entering drainage or storm water systems .

Silt barriers have been used to reduce the loss of top soil and similar particulates from construction sites and other locations. A typical known silt barrier

comprises a fence-like structure including a flexible fabric sheet of a filtration material supported by a number of posts or stakes which extend into the ground and which support the flexible fabric sheet in a generally vertical orientation.

The known type of silt barrier described above can suffer from a number of problems in use. For example, if the posts or stakes are knocked over, for example, by a vehicle entering or leaving the construction site or other location, the filtration material adjacent the fallen post will typically lie flat and not serve its intended purpose as a silt barrier. Even if a vehicle passing over the barrier avoids the posts, it may compress the filtration material into the ground and/or cause it to become

disconnected from one or more of the posts, rendering at least part of the silt barrier inoperative. Moving and re-deploying the silt barrier to allow passage of a vehicle without damaging the silt barrier is time consuming and inconvenient. Furthermore, the posts, being substantially rigid and extending upwardly from the ground may constitute a safety hazard as they may be accidentally walked into or fallen upon.

Summary of the Invention

According to a first aspect of the invention there is provided a modular unit for a silt barrier, the unit comprising:

at least one filter element which, in use, has a height direction, a width direction and a length direction and is adapted to allow the passage of water therethrough in the width direction and to resist the passage of silt therethrough in the width direction; and

a ground engageable base to which the at least one filter element is attached, in use, whereby the at least one filter element projects upwardly from the base when the base is engaged with the ground, the filter element being resiliently deformable downwardly in order to allow passage of a wheeled vehicle thereover, and such as to substantially recover its height after such deformation so that the integrity of a silt barrier of which the modular unit is a part, is maintained.

Preferably the unit has a length of at least 1 metre. Preferably the unit has a length of between 1 metre and 5 metres .

Preferably the unit has a length of between 2 metres and 4 metres .

Preferably the at least one filter element is

compressible downwardly in order to allow passage of a wheeled vehicle thereover.

Preferably the at least one filter element is

resiliently deformable downwardly towards the ground engageable base.

In an embodiment the at least one filter element is resiliently deformable downwardly against the ground engageable base. At least one filter element may comprise a block of filter material.

Preferably the ground engageable base is adapted to lie upon the ground in use.

Preferably the ground engageable base provides a substantially planar lower surface adapted to lie

substantially flat upon the ground in use.

The ground engageable base may comprise a bottom part of said block of filter material.

The ground engageable base may comprise a bottom surface of said block of filter material.

The ground engageable base may be discrete from the filter element, and the at least one filter element may be attached thereto in use.

The at least one filter element is preferably adapted to be resiliently deformable downwardly to a height no more than half its original height and to substantially recover its height after such deformation.

The at least one filter element is preferably adapted to be resiliently deformable downwardly to a height no more than a quarter of its original height and to

substantially recover its height after such deformation.

The at least one filter element may be permanently attached to the ground engageable base.

The at least one filter element may be temporarily attached to the ground engageable base.

The attachment of the at least one filter element to the ground engageable base may be adapted to allow

disassembly when not in use.

The attachment of the at least one filter element to the ground engageable base may be adapted to allow

repeated assembly and disassembly.

At least one filter element may be attached to a connection element, which is adapted to connect to the ground engageable base.

The at least one filter element may be permanently attached to the connection element. The at least one filter element may be upstanding from the connection element.

The attachment of the connection element to the ground engageable base may be adapted to allow disassembly when not in use.

The attachment of the connection element to the ground engageable base may be adapted to allow repeated assembly and disassembly.

The connection element and the base may comprise respective interlocking connection parts.

The respective interlocking parts may comprise at least one projection on one of the connection element and the ground engageable base, adapted to be received and retained in one or more respective receiving portions provided on the other of the connection element and the ground engageable base.

The one or more respective receiving portions may comprise one or more respective recesses adapted to receive one or more respective projections.

The or each projection may comprises a narrower portion and a wider portion, and a corresponding recess preferably comprises a narrower portion and a wider portion, the wider portion of the projection being adapted to be retained in the wider portion of the recess.

The projection may be adapted to be retained in the recess in use, and to be removable therefrom, by virtue of resilience and/or deformability of the projection and/or material defining the recess.

The one or more respective receiving portions may comprise one or more respective retaining projections on one of the connection element and the ground engageable base, adapted to engage one or more respective projections on the other of the connection element and the ground engageable base in order to maintain retention of a filter element relative to the base.

One or more receiving portions or projections may be adapted to be displaced by deformation of the connection element and or the ground engageable base in order to allow connection and/or disconnection of the connection element and the ground engageable base.

The base is preferably made from an impermeable material .

The base preferably extends beyond the filter

element (s) in the width direction.

The base may have one or more bevelled edges .

The bevelled edges may extend in a length direction of the unit.

The bevelled edges are preferably adapted to

facilitate flow of fluid towards the filter element (s).

The filter element (s) may be formed as a non-woven assembly of loosely looped or coiled strands.

Preferably the at least one filter element comprises a multiplicity of bonds, each bond being a bond between a point on a strand and another point on the same, or a different, strand.

Preferably the one or more strands of material are formed of a polymer material.

Preferably the one or more strands of material are formed of a plastic.

Preferably the one or more strands of material are formed of a vinyl .

An example of a material, comprising one or more strands configured in a loose looped configuration, which can be used as the filter medium is that used for vinyl non-woven matting material . An example of such a material is that used in scraper matting sold by 3M under the trade mark NOMAD (although when used for matting the vinyl strand non-woven material is typically provided as a layer approximately 1cm high which is unsuitable for use as a silt barrier in the embodiments described herein) .

The non-woven assembly of loosely looped or coiled strands may comprise an open web of interengaged

continuous coarse elements of resilient thermoplastic polymeric material, welded together at points of mutual contact to form an integrated structure.

At least one major surface of the integrated

structure may be flattened.

A first horizontally extending portion of the

integrated structure may have a higher concentration of filaments than a second horizontally extending portion of the integrated structure.

The first horizontally extending portion of the integrated structure may be closer to a bottom of the filter element than is the second horizontally extending portion of the integrated structure.

The silt barrier may comprise a substantially

continuous layer of material bonded to at least some of the filaments of the integrated structure.

The filaments may have a diameter of between about 5 and about 200 thousands of an inch (about 0.013mm to about

0.5mm)

The base may be a water impermeable sheet of

material .

The base may be formed as a solid sheet of vinyl or other plastics or rubber material.

The base may be formed by compression and/or heating of part of at least one filter element, or of the same material that forms the filter element, to provide a water impermeable base part.

The base may extend laterally beyond the filter element (s) along one or both lateral sides of the filter element.

The base may be formed with one or more securing portions to facilitate securing the base to the ground.

One or more securing portions may comprise one or more apertures through which fasteners such as securing pegs may extend.

The base may be provided with shaped end portions adapted to interlock with shaped end portions of bases of similar adjacent units.

One or more contact portions may be provided in relation to a shaped end portion so that one or more contact portions of the unit are brought into contact with one or more contact portions of a similar adjacent unit when the shaped end portion interlocks with a shaped end portion of an adjacent unit.

One or more shaped end portions may comprise a filter element or part of a filter element.

One or more filter elements may be provided in relation to a shaped end portion so that one or more filter elements of the unit are brought into contact with one or more filter elements of a similar adjacent unit when the shaped end portion interlocks with a shaped end portion of an adjacent unit.

Preferably one or more filter elements have a

thickness in their width direction of at least 10mm.

In an embodiment one or more filter elements have a thickness in their width direction of at least 20mm.

In an embodiment one or more filter elements have a thickness in their width direction of at least 40mm.

In an embodiment one or more filter elements have a thickness in their width direction of at least 60mm.

In an embodiment one or more filter elements have a thickness in their width direction of at least 100mm.

Preferably one or more filter elements have a height, in the height direction, of at least 100mm.

In an embodiment one or more filter elements have a height, in the height direction, of at least 200mm.

In an embodiment one or more filter elements comprise blocks of filter medium.

In an embodiment one or more filter elements have a length of at least 1 metre.

In an embodiment one or more of the filter elements each have a width which is more than one hundredth the length of the filter element.

In an embodiment one or more of the filter elements each have a width which is more than a twentieth of the length of the filter element. Preferably each filter element is adapted to be stably self-supporting when supported only at a bottom part thereof.

Preferably, the width of a given filter element is sufficiently great compared to the height of the filter elements to allow the filter element to be stably self- supporting when supported only at a bottom part thereof .

In an embodiment the width of a given filter element is at least one fifth of the height of the filter element.

In an embodiment the width of a given filter element is at least one quarter of the height of the filter element .

In an embodiment the width of a given filter element is at least one half of the height of the filter element.

In an embodiment the width of a given filter element is approximately the same as the height of the filter element .

The base may be provided with one or more securing portions to facilitate securing the base to the ground.

The securing portions preferably comprise apertures which extend through the base.

The base may be provided with a number of

discontinuities extending in the width direction.

The base may comprise a number of base portions separated by discontinuities.

The base may be configured with several base portions separated by discontinuities in the form of slots to facilitate flexibility of the base portion.

A plurality of filter elements may be provided on a single base.

The plurality of filter elements may be arranged in rows on the base.

One or more rows may be continuous and extend

substantially the entire length of the base.

One or more rows may be discontinuous, each

discontinuous row comprising a number of spaced apart filter elements. In an embodiment, laterally adjacent discontinuous rows may provide staggered filter elements so that gaps between the filter elements of one of the adjacent

discontinuous rows do not align transversely with gaps between the filter elements of the other of the adjacent discontinuous rows.

One or more rows may be substantially straight.

One or more rows may be formed so that it is not substantially straight.

One or more rows may be periodic or wavelike in form.

One or more rows may be located on the base such that its position in the width direction varies along the length of the base. The variation may be repeated, or periodic, in the length direction of the unit. Such rows may be considered to be periodic or wavelike in form.

One or more rows may have a generally sinusoidal form, a generally square-wave form, a generally

triangular-wave form, or a generally saw-tooth form.

One or more filter elements may be periodic or wavelike in form.

One or more filter elements may be elongate in form, extend generally in the length direction of the unit, and comprise one or more portions which are oriented in a direction which is different to the length direction of the unit. The direction which is different to the length direction of the unit may comprise a direction which has a component in the length direction of the unit and a direction in the width direction of the unit.

One or more filter elements may have a generally sinusoidal form, a generally square-wave form, a generally triangular-wave form, or a generally saw-tooth form.

Different filter elements (or rows) of different heights may be provided.

In this case it is preferred that a filter element (or row) of lesser height is provided closer to the side of the base from which it is intended water will flow, and that a filter element (or row) of greater height is provided further from the side of the base from which it is intended water will flow.

According to a second aspect of the present invention there is provided a silt barrier comprising a plurality of modular units in accordance with the first aspect of the invention.

The silt barrier may further comprise a sheet filter material .

Preferably the filter material comprises a fabric. Preferably the filter material comprises a

geotextile .

The sheet filter material may be attached to one or more units so as to mutually secure two or more adjacent units .

The sheet filter material may be attached to one or more units so to bridge one or more gaps between adjacent units .

The sheet filter material may be attached to one or more units so as to bridge one or more gaps between adjacent filter elements. (This arrangement is

particularly applicable where the one or more gaps are gaps between filter elements which are part of a row of filter elements with gaps between the filter elements of the row. )

The sheet filter material may be arranged over a surface of one or more filter elements to enhance the filtering capability of the filter element (s) .

In an embodiment the silt barrier comprises a

covering for at least a part of at least one filter element, the covering comprising a filter material to enhance the filtering capability of the silt barrier. At least part of the covering may overlie one or more

surfaces of a filter element. Preferably the covering comprises a sheet filter material.

According to a third aspect of the present invention there is provided a silt barrier comprising at least one block of material having a width, a height and a length, - li the silt barrier being adapted to allow passage of water therethrough in the width direction and to resist the passage of silt therethrough in the width direction, the block having a width at least a fifth of its height and adapted, in use, to be supported at a bottom thereof and to be otherwise self-supporting.

The silt barrier in accordance with the third aspect may be a modular unit, adapted to form an elongate silt barrier of desired length when used with one or more similar or identical modular units.

Preferably the block is sufficiently resilient to return to substantially its original height after having been compressed in the height direction by of passage of a vehicle thereover.

According to a fourth aspect of the present invention there is provided a silt barrier comprising a number of blocks of resilient material abutting or connected to form an elongate silt barrier.

According to a fifth aspect of the present invention there is provided a silt barrier comprising a plurality of filter elements, each filter element, in use, having a height direction, a width direction and a length direction and being adapted to allow the passage of water

therethrough in the width direction and to resist the passage of silt therethrough in the width direction.

Preferably, the filter elements are resilient.

Preferably the filter elements are adapted to be deformed by application of a force in a substantially vertical direction, and to return substantially to their height before deformation.

Preferably the filter elements are adapted to be compressed by application of a force in a substantially vertical direction, and to return substantially to their height before compression.

Preferably the filter elements are adapted to be compressed in their height direction by a vehicle passing thereover. Preferably the filter elements comprise a filter medium.

Preferably the filter medium comprises a single type of material which combines: (a) filtration characteristics adequate to provide an effective silt barrier and; (b) deformation/resilience characteristics adequate to allow said filter element to return substantially to its

original height after being compressed in its height direction by a vehicle passing thereover.

Preferably the filter elements comprise a filter medium comprising one or more strands of material

configured in a loose looped configuration.

Preferably the silt barrier comprises a number of modular units, each modular unit comprising at least one said filter element.

Preferably the silt barrier, in use, comprises a filter material arranged to extend between at least two adjacent modular units.

Preferably the filter material is arranged to reduce or prevent unfiltered flow of a liquid between adjacent modular units .

Preferably the filter material is a sheet filter material .

Preferably the filter material is a flexible sheet filter material.

Preferably the filter material is a geotextile.

According to a sixth aspect of the present invention there is provided a method of constructing a silt barrier comprising :

providing a number of modular silt barrier units, each of which comprises at least one filter element which, in use, has a height direction, a width direction and a length direction and is adapted to allow the passage of water therethrough in the width direction and to resist the passage of silt therethrough in the width direction; arranging a plurality of said modular silt barrier units so that each modular silt barrier unit is adjacent at least one other modular silt barrier unit and so that the plurality of modular silt barrier units comprise a silt barrier in a desired location.

In an embodiment at least one of the modular silt barrier units comprises a modular unit in accordance with a first aspect of the present invention.

In an embodiment at least one of the modular silt barrier units comprises a block of resilient material.

In an embodiment at least one of the modular silt barrier units comprises least one block of material having a width, a height and a length, being adapted to allow passage of water therethrough in the width direction and to resist the passage of silt therethrough in the width direction, the block having a width at least a fifth of its height and adapted, in use, to be supported at a bottom thereof and to be otherwise self-supporting.

Preferably at least one of the modular silt barrier units comprises a base and at least one filter element which projects upwardly from the base when the base is engaged with the ground, the filter element being

resiliently deformable downwardly in order to allow passage of a wheeled vehicle thereover, and such as to substantially recover its height after such deformation so that the integrity of a silt barrier of which the modular silt barrier unit is a part, is maintained.

Preferably the method further comprises the step of arranging a filter material to extend between at least two adjacent modular silt barrier units.

Preferably the filter material is arranged to reduce or prevent unfiltered flow of a liquid between said adjacent modular units.

Preferably the filter material is a sheet filter material .

Preferably the filter material is a flexible sheet filter material.

Preferably the filter material is a geotextile.

Preferably the method further comprises the step of attaching the filter material to at least one of the modular silt barrier units.

In an embodiment the method further comprises the step of wrapping the filter material at least partially around at least one of the modular silt barrier units.

It will be appreciated that features described in relation to one or more of the aspects of the invention may be incorporated in one or more of the other aspects of the invention.

Brief Description of the Drawings

Embodiments of the invention will now be described, by way of example only, with reference to the accompanying drawings in which:

Fig. 1 is a perspective view of an embodiment of a silt barrier, formed from a number of modular lengths, in accordance with an aspect of the present invention;

Fig. 2 is a perspective view of a single modular length of the embodiment of Fig. 1;

Fig. 3 is a cross-sectional view in a width

direction, corresponding to Fig. 2;

Fig. 4 is a plan view from above of a variation of the modular length of silt barrier of Fig. 2;

Fig. 5 is a schematic perspective view part of an embodiment similar to the embodiment of Fig. 1 in which parts forming the silt barrier are partially covered by a sheet filter material;

Fig. 6 is a schematic perspective view of a unit which can provide a modular length of an alternative embodiment ;

Fig. 7 is a cross-sectional view in a width

direction, corresponding to the embodiment of Fig. 6;

Fig. 8 is a plan view of the embodiment of Figs. 6 and 7;

Fig. 9 is a schematic transverse cross -sectional view of a silt barrier as illustrated in Figs. 6 to 8, illustrating use of fixing elements to secure the silt barrier to the ground;

Fig. 10 is a plan view of two modular lengths of sections of silt barrier, each in accordance with the embodiment of Figs. 6 to 8, illustrating how they can fit together to form a length of silt barrier;

Fig. 11 is an enlargement of the adjacent ends of the two lengths of silt barrier illustrated in Fig. 10;

Fig. 12 is a schematic perspective view of a modular length of a further alternative embodiment;

Fig. 13 is a plan view of the embodiment of Fig. 12;

Fig. 14 is a plan view of the embodiment of Fig. 12 but showing an alternative filter medium arrangement;

Fig. 15 is a cross-sectional view in a width

direction, corresponding to the embodiment of Figs. 12 to 14;

Fig. 16 is a plan view of two sections of silt barrier, each in accordance with the embodiment of Figs. 12 to 15, illustrating how they can fit together to form a length of silt barrier;

Fig. 17 is a perspective view of an alternative embodiment of a unit of a silt barrier;

Fig. 18 is an exploded perspective view of the unit of Fig. 17;

Fig. 19 is an end view of a base part of the unit of

Figs. 17 and 18;

Fig. 20 is an end view of a filter element part of the unit of Figs. 17 and 18;

Fig. 21 is an end view of the base part illustrated in Fig. 19 and the filter element part illustrated in Fig. 20, in proximity;

Fig. 22 is an end view of the base part illustrated in Fig. 19 and the filter element part illustrated in Fig. 20, mutually connected;

Fig. 23 illustrates, in enlargement, connection of interlocking parts of the base part illustrated in Fig. 19 and the filter element part illustrated in Fig. 20; Figs. 24(a) and 24 (b) illustrate schematically variations of the embodiment of Figs. 17 to 23, adapted to provide silt barriers with different numbers of filter elements ;

Figs. 25(a), 25(b) and 25(c) illustrate schematically variations of the embodiments of Figs. 17 to 24, in which the interlocking parts have a different shape;

Figs. 26(a), 26(b) and 26(c) illustrate schematically variations of the embodiments of Figs. 25(a), 25(b) and 25(c), in which the interlocking parts have a different shape ;

Fig. 27 is an end view of a further alternative embodiment of a unit of a silt barrier, comprising a base part and a filter element part attachable to the base part;

Fig. 28 is an end view of the base part and filter element part, illustrated in Fig. 27, separate, and in proximity;

Fig. 29 illustrates, in enlargement, connection of base part and filter element part of Figs. 27 and 28;

Fig. 30 is an end view of a further alternative embodiment of a unit of a silt barrier, comprising a base part and a filter element part attachable to the base part;

Fig. 31 is an end view of the base part and filter element part, illustrated in Fig. 30, separate and in proximity;

Fig. 32 illustrates, in enlargement, connection of base part and filter element part of Figs. 30 and 31;

Fig. 33 is a perspective view of an alternative embodiment of a silt barrier in accordance with an aspect of the present invention;

Fig. 34 is a schematic horizontal cross-sectional view of the silt barrier of Fig. 33; and

Fig. 35 is a schematic plan view of a length of silt barrier in which the embodiment of Figs. 33 and 34 is used as part of the length and in which a conventional silt barrier arrangement is used as another part of the length.

Detailed Description of the Drawings

With reference to Fig. 1 an embodiment of a silt barrier, generally designated 10, comprises a number of units each comprising a block of material through which water can flow, the units being adapted to be aligned end to end in order to provide an elongate silt barrier 10.

As illustrated in Fig. 1 the silt barrier 10

comprises a first end unit 11, a number of intermediate units, of which first and second intermediate units 12, 13, respectively are illustrated and a second end unit 14. In the illustrated embodiment each unit is substantially identical and thus only one of the units will be described in detail hereafter. However, it should be appreciated that in this embodiment each unit 11, 12, 13, 14 comprises a block of material and a base attached to the block, the base being securable to the ground in order to secure the unit in position.

With reference to Figs. 2 and 3 one of the units, in this example the second end unit 14, will be illustrated and described in more detail. The block of material 15 of the second end unit 14, in this embodiment, is in the form of an elongate, generally cuboid block of water permeable material, which is attached to an upper surface of the base 16, but which is otherwise self supporting. That is, it does not require posts or stakes to maintain the orientation and height of the block 15. In this

embodiment the block 15 has a width dimension, designated X of approximately 70mm, a length dimension, designated Y, of approximately 1500mm and a height dimension, designated Z, of approximately 230mm. It will be appreciated that these dimensions may be varied as desired, according to the intended circumstances of use and desired

characteristics of the silt barrier. In alternative embodiments the width of the block may be greater, for example 100mm or smaller, for example 50mm, in order to provide desired characteristics.

Unit 14, is in use, positioned to form part of a silt barrier 10 such that run-off water, for example rain water draining from a construction site, can pass through the block 15 in its width direction, and so that silt (which in this context is used to include dirt, sand, and other particulate matter which forms soil, or removal of which might contribute to erosion of a land area) is prevented from passage through the block, by the block structure. In this embodiment the block 15 is formed from a non- woven, somewhat irregular mesh of vinyl strands, in which points of contact between the strands (or points where a curved strand contacts itself) provide adhesion or other attachment so that the structure of the mesh is

maintained. The strands are preferably of vinyl, and the open, non-woven mesh is similar in structure to that used in scraper matting such as that manufactured by 3M and sold under the trade mark NOMAD. This material is

sometimes referred to as "vinyl loop" material . Vinyl loop scraper matting is known to be resilient in nature, that is, a layer of vinyl loop material typically about 10mm thick, as used in scraper matting, is known to return to its original height after being compressed, for example by being stepped on during use. Details of the structure of, and a manufacturing method for, an open looped

material can be found in US Patent No. 3, 837,988, the contents of which are included herein by reference. Of course, it will be appreciated that the structure, or method of manufacture of, the looped material for use in filter elements in accordance with the present disclosure is not limited to the structure or method of manufacture described in that document. The material may comprise a non-woven assembly of loosely looped or coiled strands which form an open web of interengaged continuous coarse filaments of resilient thermoplastic polymeric material, welded together at points of mutual contact to form an integrated structure. A face, or major surface, of the integrated structure may be flattened. Thus, in

accordance with embodiments disclosed herein, the filter elements may comprise blocks or strips of said non-woven assembly of loosely looped or coiled strands which form an open web of interengaged continuous coarse filaments of resilient thermoplastic polymeric material.

A first horizontally extending portion of the

integrated structure may have a higher concentration of filaments than a second horizontally extending portion of the integrated structure. The first horizontally

extending portion of the integrated structure may be closer to a bottom of the filter element than is the second horizontally extending portion of the integrated structure. The base may comprise a substantially

continuous layer of sheet material bonded to at least some of the filaments of the integrated structure. The

filaments may have a diameter of between about 5 and about 200 thousands of an inch (about 0.013mm to about 0.5mm). If desired, the base may be formed by compression and/or heating of part of at least one filter element, or of the same material that forms the filter element, to provide a water impermeable base part.

It will be appreciated that the dimensions of the block 15 are very different to the dimensions of vinyl loop material used in scraper matting. That is, the block 15 has considerably greater height than the height of vinyl loop material in scraper matting in order to prevent run-off water merely flowing over the top of the block. The described embodiment takes advantage of the resilient nature of vinyl loop material to provide a block 15 which is of simple, generally uniform construction and is highly permeable to water (allowing good drainage in its width direction) but which can trap silt carried by the water which passes into the block in order to act as a silt barrier. Furthermore, the resilient qualities of the material are utilized to provide a silt barrier over which pedestrian or vehicular traffic may pass, so that the block (and thus the silt barrier) can return to its original height quickly after being compressed by passage of such traffic thereover. It should however be

appreciated that in alternative embodiments the block could be formed from suitable alternative resilient water permeable materials, such as suitable permeable foam materials known for use as filter media.

With further reference to Figs. 2 and 3, the base 16 in this embodiment comprises first, second and third base portions 17, 18, 19 respectively. Each base portion 17, 18, 19 is generally in the form of a slab of durable material such as a suitable rubber or plastic. Each base portion is provided with a number of apertures, for example apertures 21 and 22 of the first base portion 17, which extend therethrough in the height direction and via which the base portions, and thus the unit 14 can be secured to the ground by pegs (not shown) . Each base portion has a bevelled leading edge, for example bevelled edge 20 of first base portion 17, in order to assist flow of water from the ground onto the base portion.

A first slot 23 is provided between the first and second base portions 17, 18 and a second slot 24 is provided between the second and third base portions 17 , 18. Provision of the slots provides a degree of

flexibility for the unit in its length direction.

In use a number of units substantially identical to the second end unit 14 are abutted end to end in order to form an elongate silt barrier 10. The units are secured in position by use of pegs extending through the apertures (for example apertures 21, 22) . A silt barrier formed in this manner will be effective in reducing loss of silt carried by water running off a land area such as a

construction site, when correctly positioned. Further, a silt barrier provided in such a manner is likely to be more durable than a conventional fence-like silt barrier since its effective operation does not depend upon

maintaining the positions of stakes extending upwardly from the ground, nor of a fabric extending between, supported by, and attached to, the stakes. Thus passage of traffic over the silt barrier 10, even if such passage occurs with no regard to maintenance of the integrity of the silt barrier, will generally not substantially

adversely affect operation of the silt barrier. The resilient nature of the blocks (for example block 15) allows the silt barrier to return quickly to its fully operational height after passage of traffic thereover. The pegs (not shown) used to secure the units of the silt barrier to the ground will typically not extend far above ground level (that is their tops will typically be flush or almost flush with the base 16) and will generally not be adversely affected by passage of traffic thereover. It is envisaged that plastic pegs with fairly broad flat heads may advantageously be used.

If the units are positioned so that adjacent units closely abut little or no water should be able to flow through spaces between the units. However, if desired, a suitable filter material, for example a geotextile

material, could be attached to the blocks in order to bridge any gaps between adjacent units and prevent

unrestricted and unfiltered flow of water and silt through any such gaps .

In a variation of the embodiment of Figs. 1 to 3 each unit could be made with its ends shaped so as to provide a degree of overlap of the block of the unit with the blocks of adjacent units. With reference to Fig, 4 a unit 114, (which is similar in many respects to unit 14 of Figs. 1 to 3) comprises a block of material 115 mounted on a base

117. The base 117 is provided with a bevelled leading edge 120 and first, second and third vertically extending apertures 121, 122, 123, respectively. The block 115 is provided, at a first end thereof, with a longitudinal extension 130 over a part of its width and is provided at a second end with a cut-out 132 suitable for accommodating an extension (corresponding to longitudinal extension 130) of an identical unit. The shape shown in Fig. 4 is, of course, only one example of providing a block configured to overlap with adjacent blocks and it will be evident to a skilled person that many other shapes (for example tongue and groove type, dovetail type shapes or other overlapping and/or interlocking shapes) could be used.

In the embodiment of Fig. 4 the base 117 is provided with a longitudinal extension 131, on which the first aperture 121 is provided. The extension 131 is adapted to overlie part of a base of an adjacent unit so that the first aperture 121 can align with an aperture

(corresponding to aperture 123) of the adjacent unit so that a peg (not shown) can pass through apertures of both units thus securing the units together in addition to securing them to the ground.

It will be appreciated that securing the base to the ground with pegs can assist in conforming the shape of the base to the contours of the ground in order to prevent run-off water passing beneath the silt barrier. In some applications it may be desired to at least partially bury the base in order to avoid pooling of the water against the front thereof.

Fig. 5 illustrates use of a geotextile material 135 attached to blocks 136, 137 of adjacent units, similar to the units of Fig. 1. The geotextile material 135 bridges any gap which might exist between the blocks 136, 137. In this embodiment the geotextile material 135 is in the form of a sheet attached to respective front faces 136A, 137A of the blocks 136, 137. Fixings 148 such as suitable hooks, anchors or staples may be used to secure the geotextile material to the blocks 136, 137. The looped structure of the blocks of preferred embodiments allows hooks or the like to be easily secured thereto, and the skilled addressee will appreciate that such hooks can easily be passed through the geotextile material of Fig. 5 in order to allow the material to be secured to the blocks 136, 137. Using a geotextile material 135 to extend between and bridge any gaps between the blocks 136, 137 prevents unrestricted flow of water and particulate carried by the water, through any gaps which might occur between the blocks .

It will be appreciated that Fig. 5 illustrates only one example of using a geotextile or other filter material to prevent unrestricted (unfiltered) flow of water through gaps between adjacent blocks. In alternative arrangements (not illustrated) a suitable filter material (for example geotextile material) may be fastened or wrapped around the entire region where adjacent units abut. Thus the

material may be used to bridge any gap, for example, gap 139, between the bases of adjacent units as well as between blocks . In a further alternative arrangement the geotextile or other sheet filter material may be used to cover all of the exposed faces of the blocks (that is the front, rear and top faces) in the region of the abutment of two blocks. Other arrangements of bridging gaps using a sheet filter material are possible and further

variations such as using a non-sheet material, or using an impermeable sheet (or non- sheet) material could be used to bridge gaps .

It will be further appreciated that the bridging material being fastened to each of the two adjacent blocks will serve to provide some degree of structural connection between the blocks, and thus to some extent may assist in retaining the blocks in abutment even if fastening pegs are not in use.

In the embodiments of Figs. 1 to 5 each base is provided with a single block of filter material thereon, and may therefore be regarded as having a single, large, filter element thereon. However, the present disclosure encompasses additional embodiments which provide barriers to flow of silt over a base. In particular, bases may be provided with different arrangements of filter elements thereon which allow flow of water over the base but prevent or reduce passage of silt. In relation to one such embodiment, an example of a unit, generally designated 1200, for forming a silt barrier of any desired length, will now be described with reference to Figs. 6 to 11. The unit 1200 comprises a base 1216, with a number of discrete filter elements (in this embodiment three filter elements) provided thereon. It will be appreciated that the base 1216 is similar to the base 16, and only differences will be described in detail hereafter. The base 1216 is generally rectangular with (in this embodiment) a length of 3 metres and a width of 0.5 metres, has a respective bevelled region 1220a, 1220b along each of its long sides and can serve as a barrier for water flowing from either side. Apertures, for example apertures 1221, 1222, for receiving fixing pins or pegs, are provided in the bevelled regions 1220a, 1220b.

Provided on the base 1216 are three elongate filter elements 1211 to 1213 respectively. The filter elements 1211 to 1213 are orientated in the length direction of the unit 1200, extend substantially the entire length of the unit 1200, and are spaced across the lateral width of the base 1216.

Fig 9 illustrates schematically the use of fixing pins 1224, 1225 to secure the base 1216 to the ground (not shown) . Shafts of the fixing pins extend through the apertures (eg 1221) provided in the bevelled regions

1220a, 1220b for this purpose.

It will be appreciated that the unit 1200 is provided with transversely offset longitudinal extensions 1231, 1232 at the ends thereof, which enable two or more similar units 1200, 1201 (see Figs. 10 and 11) to overlap in the longitudinal direction when placed adjacent each other to form a silt barrier of a desired length. The longitudinal overlap assists in reducing flow of silt-carrying water through any gap between adjacent units. Furthermore, if desired or deemed necessary, a geotextile material may be used to bridge any gap between adjacent units, for example by being attached to and or wrapped around adjacent filter elements of adjacent units.

It has been found that filter elements dimensioned and distributed as described, and made of the loose looped vinyl material described above, can provide adequate filtration for at least some silt barrier

applications, and when suitably attached to the base can return to substantially their original heights after being deformed and compressed by passage of a person or vehicle thereover. The filter elements 1211 to 1213 may be attached to the base by a suitable adhesive. Preferably a jig is used during assembly to facilitate correct placement of the filter elements during assembly and retention of the filter elements in position while the adhesive sets and/or cures.

In the illustrated embodiment, the filter element 1211 closest to the leading edge (ie the edge from which it is anticipated that water will normally flow, in use) is shortest, at about 100mm high. The next (central) filter element 1212 is of intermediate height, being about 150mm high, and the rearmost filter element 1213 is tallest, being about 200mm high. Of course this does not preclude other variations in configuration or distribution of filter elements. Providing filter element heights which increase with the direction of water flow (ie increase in height from the leading edge of the unit) has been found to contribute to effective flow of water across the barrier under some circumstances, while still

providing adequate filtration. Of course it will be appreciated that the dimensions provided are by way of example and may be varied according to the intended circumstances of use and desired characteristics of the silt barrier.

It will be appreciated the filter elements can return to their original heights after compression or deflection, for example by passage of a vehicle over the unit 1200. For the filter medium used in an effective prototype, which is the loose looped vinyl material described above, it has been found that a filter element width of

approximately 50 mm is required in order to allow a simple elongate filter element of the type illustrated to

reliably return to substantially its original height.

In this and other embodiments, if it is desired to change the filtration characteristics for a particular set of circumstances, the distribution, thickness or strand density (or other filtration characteristics, especially if a different type of filter medium is used) of the filter medium may be changed accordingly. Further, if desired a geotextile (or other filter) material can be attached to one or more of the filter elements. In this case is it preferred that additional filter material be attached to the leading face of the filter element.

Further other suitable supplementary filter media could be included - for example an insert made from a resilient foam filter medium could be attached between two filter elements .

It will be appreciated that fewer or more than three elongate filter elements (or rows of filter elements) may be provided if desired and that the width (which may be regarded as the transverse thickness) of each filter element may be selected according to the conditions of use and filtration characteristics required. Although use of filter elements which extend continuously substantially the entire length of the unit is preferred, in one

alternative one or more such filter elements could be replaced by a row comprising a number of filter elements of lesser length, either abutting or spaced slightly apart so that water can flow between adjacent filter elements of the row. In such an embodiment it is desirable to offset the spaces in the different rows, and/or have at least one continuous filter element extending the length of the unit and/or use additional filter material, in order to prevent unfiltered water carrying excessive silt across the barrier. In one such embodiment the filter elements in a given row are each approximately 100mm long (in the length direction of the unit 1216) and are spaced apart (in the length direction of the unit 1216) by about 20mm, and the filter elements of adjacent rows are staggered to create an interrupted turbulent flow of water across the unit, which can assist in preventing silt being carried across the barrier. Of course, it will be appreciated that many further variations in the size, shape and/or distribution of the filter elements on the base are possible.

Figs. 12 to 16 illustrate a unit, generally

designated 1300, which is a further variation. A base 1316 of unit 1300 is similar to the base 1216 of unit 1200. Like unit 1200, the unit 1300 has three continuous rows 1311, 1312, 113 of filter elements, each of which is formed as a single filter element which extends

substantially the entire length of the unit 1300. However, in the unit 1300 the rows are wavy, or approximately sinusoidal in form, rather than extending in a straight line along the length of the unit. In this embodiment the filter elements are approximately 20mm in thickness, but the wavy or sinusoidal form of each extends about 100mm (peak to trough) in the width direction of the unit 1300. The wavy form of the filter elements has been found to enhance the ability of the filter elements to return to their original heights. That is, a straight elongate filter element, for example 20mm thick and 100mm high would be likely to be deflected (ie folded down) by passage of a vehicle thereover, and might therefore be unable to return to its original height, whereas the sinusoidal or wavy form of the filter elements of unit

1300 helps prevent such deflection, resulting instead in compression, from which the filter elements can more easily recover substantially their original heights. A unit with this form of filter element can be manufactured by providing a jig with a formers or guides shaped

according to the desired shape of the filter elements, placing straight sections of filter material in the jig so that they are held in the desired (eg sinusoidal) shape, and adhering or solvent welding the shaped filter material to the base. After curing, the jig can be removed and the desired shape of the filter elements is retained by adherence to the base. It will be noted that the width dimensions of end projections 1331, 1332 may be adapted to accommodate the form of the filter elements and ensure that filter elements on adjacent units 1300, 1301 (see Fig. 16) abut with minimal space therebetween.

The wavy filter elements may each be formed from a number of lengths of filter material, as illustrated in Figs. 12 and 13, or may be formed from a single length of filter material, as illustrated in Fig. 14. It will be appreciated that the filter elements may take other wavy, curved, serpentine, shaped and/or periodic forms, such as, but not limited to, a square-wave form, a triangle or zigzag wave form, or a saw tooth form. Regularity in the form, and a relatively frequent periodicity are normally desirable in order to avoid uneven flow across the silt barrier, but may not always be necessary. As a further variation some other arrangement may be incorporated to reduce or avoid deflection of the filter elements: for example the filter element material could be set out as a square grid on the base, each side of each square of the grid assisting the perpendicular neighboring sides to resist deflection. In another alterative embodiment the filter elements are shaped so that they are wider at their bottoms than at their tops and may, for example, be triangular, truncated-triangular or trapezoid in

transverse cross section: it will be appreciated that such a tapered shape may result in a filter element having an reduced tendency to be deflected and a greater tendency to be substantially vertically compressed. However, the generally sinusoidal form of the filter elements of the illustrated unit 1300 has been found to be effective, economical in its use of filter material and convenient.

A further embodiment is illustrated in Figs. 17 to 23, which show a unit, generally designated 1400, which has a single sinusoidal filter element 1411 which may be detached from a ground engaging base 1416 (It will be appreciated that variations with more than one filter element, or filter element row, are possible) . The unit 1400 has many similarities to the unit 1300, but rather than having one or more filter elements permanently attached to a base 1316, at least one filter element 1411 is attached to a connection element 1480 which is

attachable to, and detachable from, the base 1416. The connection element 1480 comprises a generally planar portion 1483 upon an upper surface of which the filter element 1411 is permanently attached (for example, in a similar manner to that in which the filter element 1311 is attached to the base 1316) . The base 1416 may have beveled edges 1420, and the connection part 1480 may also have beveled edges 1484.

The connection element 1480 further comprises a downwardly projecting part which projects generally perpendicular from the generally planar portion and is adapted to fit into the base 1416. The downwardly

projecting part comprises a narrower part 1481 closer to the generally planar portion 1483, and a wider part 1482 distal from the between generally planar portion 1483. The base 1416, in this embodiment, provides a shaped groove for receiving and retaining the downwardly

projecting part, the shaped groove 1490 comprising a shallower narrower portion 1491 and a deeper wider portion 1492. The downwardly projecting part and the groove may extend the entire length of the unit 1400. It will be appreciated that once inserted into the groove the wider part 1482 of the downwardly projecting part will be retained in the wider part 1492 of the shaped groove as it is too wide to pass through the narrower part 1491 of the groove.

In the illustrated unit 1400, the wider part 1482 of the downwardly projecting part can be introduced into the wider part 1492 of the groove by sliding it thereinto from one end of the groove, and progressively sliding the downwardly projecting part, axially, into the entire length of the groove. In the unit 1400, as illustrated, the groove is dimensioned to provide some clearance around the downwardly projecting part, in order to provide a slightly loose fit and avoid undue friction. That is, relevant dimensions of the downwardly projecting part are slightly smaller than corresponding dimensions of the groove. More specifically, and by way of example, in the illustrated unit 1400: the width of the narrower part 1481 of the downwardly projecting part is 19mm and the width of the narrower part 1491 of the groove is 20mm; the width of the wider part 1482 of the downwardly projecting part is 39mm and the width of the wider part 1492 of the groove is 40mm; and the vertical height of the wider part 1482 of the downwardly projecting part is 8mm whilst the vertical height of the wider part 1492 of the groove is 10mm.

Further, in this example, the vertical height of the narrower part 1481 is slightly greater than the vertical height of the narrower part of the groove (eg 1mm, or 10%, greater) which also assists in avoiding undue friction. Of course, it will be appreciated that other dimensions are possible.

In one alternative, in a suitably formed embodiment, the wider part 1482 of the downwardly projecting part can be introduced into the wider part 1492 of the groove by inserting it directly (eg vertically downwardly, or otherwise transversely) after the base 1416 has been folded (or bent) somewhat along its centerline, in order to temporarily widen the narrower part 1491 of the groove, allowing ingress of the wider part 1482 of the downwardly projecting part. When the base engages the ground by lying thereupon, such bending (and consequent widening of the narrower part of the groove) is substantially

prevented, so the downwardly projecting part will be effective retained in the groove, and inadvertent disconnection avoided.

In a further alternative, the wider part 1482 of the downwardly projecting part may be sufficiently deformable and resilient to be manually forced into the wider part of the groove and be retained therein. In such an embodiment the wider part 1482 of the downwardly projecting part may be provided with one or more cavities, preferably one or more elongate axially extending cavities, therein to facilitate providing the required deformation.

It will be appreciated that variations are possible.

For example a base may be adapted to receive two or more connection parts. Fig. 24(a) illustrates a base 1516 having first to third grooves 1590, 1591, 1592, each adapted to receive a downwardly projecting part of a connection part 1580, 1581, 1582. Fig. 24(b) illustrates a base 1616 having first and second grooves 1690, 1691, each adapted to receive a downwardly projecting part of a connection part 1680, 1681. Clearly, the number of grooves may be selected as desired. Figs. 24(a) and 24(b) thus illustrate schematically variations of the embodiment of Figs. 17 to 23, adapted to provide silt barriers with different numbers of connection elements and filter elements. It will also be appreciated that the or each connection part may be provided with more than one filter element (or row of filter elements) if desired.

Figs. 25(a), 25(b) and 25(c) illustrate

schematically, in transverse cross section, variations (1700, 1701, 1702, respectively) of the embodiments of Figs. 17 to 24(b), in which the interlocking parts have a different shape. That is, the wider parts 1782 of the downwardly projecting parts are generally circular in transverse cross section. Such embodiments are well suited to a variation (described above) in which the wider parts 1782 of the downwardly projecting parts have

elongate axially extending cavities or through bores (not shown) to allow greater deformation and insertion by passing through the narrower parts of the grooves. Figs. 26(a), 26(b) and 26(c) illustrate

schematically, in transverse cross section, further variations, 1703, 1704, 1705 respectively, of the

embodiments of Figs. 17 to 25(c), in which the

interlocking parts, eg 1782A, have a different shape.

It will be appreciated that the filter elements are omitted from Figs. 24(a) to 26(c) for convenience. Units in accordance with the embodiments of Figs. 17 to 26(c) could be factory assembled, or provided for assembly on- site. Further, a bonding agent or adhesive could be used to render assembly permanent, or could be omitted to allow disassembly as required, which would facilitate storage and transportation of the units.

In further embodiments, not illustrated, each

connection part may be provided with more than one

downwardly projecting part, each adapted to be received in a corresponding receiving part of a base.

A further embodiment is illustrated in Figs. 27 to 29, which show a unit, generally designated 1800, with a filter element 1811 which may be detached from a ground engaging base 1816 (It will be appreciated that variations with more than one filter element, or filter element row, are possible) . The unit 1800 has many similarities to embodiments described above, but comprises a different attachment arrangement for attaching the filter element 1811 to the base 1816.

In the unit 1800, at least one filter element 1811 is permanently attached to an upper part of a connection element 1880 which is attachable to, and detachable from, the base 1816. The connection element 1880 is in the form of a downwardly projecting part which is generally

rectangular in transverse cross section and which has generally parallel sides 1882 which are typically oriented generally vertical in use. The downwardly projecting part is provided with resilient lugs 1883, which project outwardly and upwardly from the sides 1882. A resilient portion 1884 is provided, attached to an underside 1885 of the connection element 1880. The connection element 1880 may be formed from a suitable material, such as a suitable rubber or plastic material, and the lugs 1883 may be integrally formed as parts thereof (for example in

suitable molding or extrusion process) . The resilient portion 1884 may be any suitable resilient material, and in some embodiments may conveniently be made from a similar material to that of the filter element.

The base 1816, in this embodiment, provides a complementary groove 1890, for receiving and retaining at least part of the connection element 1880. In this embodiment the groove 1890 is generally rectangular in transverse cross section and may extend the entire length of the unit 1800. The groove, 1890 is at least partially defined by side walls 1891 (which are typically oriented generally vertical in use) and a bottom wall 1892.

Recesses 1893 are provided in the side walls 1891 for receiving and retaining the lugs 1883 of the connection part 1880.

It will be appreciated that this arrangement

facilitates attachment of the filter element 1811 to the base 1816 by forcing the connection element 1880

downwardly (into the groove 1890) relative to the base 1816 (rather than sliding the connection element into the groove as discussed in relation to some other

embodiments) . When the connection element 1880 is forced (downwardly) into the groove 1890, the lugs are received and retained in the recesses 1893, to maintain the

connection of the filter element 1811 to the base 1816. Upper walls 1894 of the recesses 1893, in this embodiment, are shaped to so that at least a part of each recess extends upwardly as it extends away from the groove, assisting secure accommodation of the lugs 1883. The upwardly directed direction of projection of the lugs and recessed facilitates connection but not disconnection.

The groove 1890, connection element 1880 and

resilient portion 1884 are dimensioned so that when the lugs 1883 are received in the recesses 1893, the resilient portion is in a state of vertical compression (between the underside 1885 of the connection element 1880 and the bottom wall 1892 of the groove 1890) and exerts an upwards biasing force on the connection element 1880. This retains the lugs 1883 securely against upper walls 1894 of the recesses. This can enhance stability of the

connection between the filter element 1811 and the base 1816.

When, and if, desired, the connection element 1880

(and filter element 1811) may be detached from the base 1816 by folding or bending the base somewhat along its centerline, in order to temporarily widen the groove 1890, and thereby increase the distance between the recesses so that the lugs are no longer retained. This can be

conveniently achieved by providing a suitable, preferably elongate, object (for example, a length of 50mm diameter pole or pipe) under the central elongate axis of the base 1816, and if necessary applying pressure to the edges of the base (for example by standing on or adjacent the beveled edges) . Thus the connection arrangement of unit 1800 can provide convenient attachment and detachment of the filter element and base.

Although the unit 1800, as illustrated, includes a single connection part, a single downwardly projecting portion, a single filter element (or row of filter

elements) and does not include a generally planar portion (such as, for example, generally planar portion 1483) which rests upon an upper surface of the base, it will be appreciated that in variations of this embodiment two or connection parts, two or more downwardly projecting portions, two or more filter elements (or rows of filter elements) and/or a generally planar portion could be provided.

The units in accordance with the embodiments of Figs.

17 to 29 provide the downwardly projecting parts and corresponding grooves along the entire lengths of the units. This can provide secure assembly, and the

connection arrangement can effectively act as a seal to prevent passage of water between the base and the

connection element (s) . However, it will be appreciated that any suitable connection arrangement could be used. For example, alternative embodiments could provide a single connection arrangement which does not extend the entire length of the unit, or could provide a number of connection arrangements spaced apart along the length of the unit. For example, in relation to use of a number of connection arrangements spaced apart along the length of the unit, many types of suitable push- in connection arrangements are known per se, and one such arrangement might comprise metal or plastic studs attached to and projecting from the connection part, each with a head adapted to be received and retained in a corresponding suitably shaped cavity in the base. Each such cavity could have one or more associated flanges or flaps, which could be resiliently deformable, adapted to retain the head of a stud in the cavity.

The bases in various illustrated embodiments (eg, those of Figs. 17 to 29) may be generally rectangular and adapted to simply mutually abut in an end- to- end

arrangement (with use of geotextile to bridge gaps between units, if appropriate) . However, it will be appreciated that the bases could, if desired, provide interlocking or overlapping axially extending parts (for example

corresponding to longitudinal extension 130 and cut-out 132) .

Further, although the embodiments of Figs. 17 to 29 are described with reference to filter elements made of a loose looped vinyl material, other types of filter element could be used. For example, a resilient sheet-like filter material, such as that disclosed in US20070042197A (the teaching of which is incorporated herein, by reference) could have a lower edge thereof embedded in the connection element, preferably extending into the downwardly projecting part thereof, and an upper part thereof

projecting upwardly from the connection element to inhibit passage of silt across the barrier.

A further embodiment is illustrated in Figs. 30 to 32, which show a unit, generally designated 1900, with a filter element 1911 which may be detached from a ground engaging base 1916 (It will be appreciated that variations with more than one filter element, or filter element row, are possible) . The unit 1900 has many similarities to embodiments described above, but comprises a different attachment arrangement for attaching the filter element 1911 to the base 1916.

In the unit 1900, at least one filter element 1911 is permanently attached to an upper part of a connection element 1980 which is attachable to, and detachable from, the base 1916. The connection element 1980 comprises a part-cylindrical resilient connection member 1981 which is, in use, aligned so that its axis of elongation is parallel to an axis of elongation of the base 1916. The connection member 1981 is generally semi-circular in transverse cross section and has a convex upper (or crown) portion 1982 upon which the filter element is mounted, and side portions 1983 which in use extend outwardly and downwardly from the upper portion. The material of the connection member 1981 is small in thickness compared to the radius of curvature thereof, and the part -cylindrical resilient member 1981 thus defines a generally part- cylindrical space 1984 therein. The connection member 1981 is adapted to overlie, and attach to, part of the base 1916. A part of the base can be received in the space 1984, as will be described.

In this embodiment the base 1916 is provided, on an upper surface thereof, with a generally semi -cylindrical projection 1990, the axis of which is generally parallel to the direction of elongation of the base 1916. The projection 1990 is adapted to be substantially received in the space 1984, so that an upper convex surface of the projection 1990 abuts a lower concave surface of the connection member 1981.

A fixing arrangement is provided for detachably fixing the connection member 1981 to the base 1916, and in the illustrated embodiment, to the projection 1990. In this embodiment the side portions 1983 of the connection member 1981 are provided with upwardly and inwardly extending projection members 1985 which extend into the space 1984 and which are received and retained by

receiving portions provided on the projection 1990. In this embodiment the receiving portions are in the form of downwardly and outwardly projecting ridges 1991 provided on respective lower side parts of the projection 1990.

In use, the filter element 1911 can be connected to the base 1916 by placing the connection member 1981 onto the projection 1990, and applying downwards pressure to the filter element and/or connection member 1981. This forces the upper portion 1982 of the connection member 1981 downwards, and the side portions 1983 downwards and outwards, so that the projection members 1985 move

vertically past the ridges 1991. (Lower parts of the projection members 1985 may engage, and be guided by, upper parts of the ridges 1991 during this downwards movement.) Release of the downwards pressure allows the side portions 1982 to move inwardly, and the projection members 1985 to be received and retained under the ridges 1991. (It will be appreciated that in alternative

embodiments alternatives to the projection members 1983 and/or ridges 1991 could be provided, for example one or more projections on the connection member or base could be received in one or more complementary, suitably formed, recesses . )

The connection element 1980 may be formed from a suitable material, such as a suitable rubber or plastic material, and the projection members 1983 may be

integrally formed as parts thereof (for example in

suitable molding or extrusion process) . The projection 1990 may be formed integrally with the rest of the base 1916, and may be resiliently deformable, to facilitate deformation of the connection member 1981. To facilitate deformation of the projection 1990 one or more cavities 1993 may be provided therein.

It will be appreciated that this arrangement

facilitates attachment of the filter element 1911 to the base 1916 by forcing the connection member 1981 downwardly (onto the projection 1990) relative to the base.

When, and if, desired, the connection element 1980

(and filter element 1911) may be detached from the base 1916 applying downwards pressure to the connection member 1981 adjacent an end of the unit 1900, to spread the side portions and projection members 1985, and applying an upwards force close to the place where the downwards force is applied, to lift the projection members 1985 at that point upwards past the ridges 1991. A suitable downwards force can be applied, for example, by standing on an appropriate part of the connection element. Disconnection can then be achieved, along the length of the unit, by lifting connection element 1980 away from the projection sequentially along the length of the unit 1900, with suitable application of adjacent downwards force (to spread the projection members 1985) as and when required.

Although the unit 1900, as illustrated, includes a single connection part, a single downwardly projecting portion, a single filter element (or row of filter

elements) and does not include a generally planar portion (such as, for example, generally planar portion 1483) which rests upon an upper surface of the base, it will be appreciated that in variations of this embodiment two or connection parts, two or more downwardly projecting portions, two or more filter elements (or rows of filter elements) and/or a generally planar portion could be provided.

The embodiments of Figs. 1 to 32 are intended for use in areas with relatively low water flow although it will be appreciated that suitable choice of dimensions and other characteristics (such as filter medium

characteristics) will affect suitability of the silt barrier with use of different drainage and water flow requirements .

With reference to Figs. 33 and 34, an alternative embodiment is illustrated. In this embodiment, generally designated 200, a silt barrier comprises a number of units each in the form of a block of material 211, 212, 213 which may be similar in composition to the blocks

described with reference to other embodiments, but which need not include a distinct base part. In this embodiment the blocks are generally elongate cuboids in form and are able to be substantially freestanding on the ground, so that a bottom surface of a block acts as a ground-engaging base. In one example of this embodiment each block 211, 212, 213 has a length of approximately one meter and a width and height of approximately 40cm. The blocks 211, 212, 213 are abutted end to end in order to provide a continuous barrier and it will be appreciated that any desired number of blocks may be used to provide a barrier of desired length. In order to enhance the filtration effected by the blocks and to secure adjacent blocks together against inadvertent separation, a sheet

filtration material such as a geotextile may be used to bridge gaps between the blocks, as would be understood from the description above. In this embodiment 200 the entire front and rear faces of the silt barrier are covered by sheet filter material (although it will be appreciated that in alternative embodiments a sheet filter material may be omitted, may cover less area and/or be used only to bridge joins between the blocks) .

It will be appreciated that there are many ways of providing sheet filter material on the front and rear faces of the silt barrier and that fixings (not shown) as described with reference to, for example, Fig. 5 provide a convenient mechanism for attaching the sheet material to the blocks .

With reference to Figs. 32 and 33 an arrangement of sheet material on the blocks will be described.

A block 211 provided at one end of the silt barrier has a first end of an elongate sheet of filter material 221 attached at a first end 211A of the block 211. The sheet material 221 extends from the first end 211A along the front face of the block 211 across a second end 211B of the first block 211 and terminates where it is secured to the first end 211A of the block 211. Thus the sheet material 221 is attached at both of its ends to the first face 211A of the block 211 and substantially covers the front, second end 211B and rear faces of the block. The sheet material will be substantially vertical in use.

A second block 212 is placed abutting the first block

(although it will be appreciated that part of the sheet material 221 which extends across the second end 211B of the first block 211 will be between the first block 211 and the second block. A second sheet of filter material 222 is attached at a first end 222A thereof to the front face of the first block 211, where it overlies part of the first sheet 221. The second sheet 222 extends along the front face of the first block 211 (overlying part of the first sheet 221) , bridges any gap between the first block 211 and the second block 212, extends along the front face of the second block 212 across the end of the second block 212 which is further from the first block, extends along the rear of the second block, bridges the gap between the second block 212 and the first block 211 and is attached at a second end 222B of the second sheet 222 to the rear face 211. Thus the second block 212 is connected to the first block 211 by the second sheet of filter material 222 and the front and rear faces of the second block 212 are covered by the second sheet of material 222.

As many block as are desired may be attached to the second and subsequent blocks in the same manner as the second block 212 is attached to the first block 211 so a silt barrier of desired length can be provided. As illustrated a third block 213 is attached to the second block 212 by a third sheet of filter material 223 which is attached at its ends 223A, 223B to the second block 212 and which covers the front and rear faces of the third block 213 and the end face of the third block which is distal from the second block 212. For illustrative purposes the first sheet 221 and third sheet 223 are illustrated in Fig. 33 by shading and the second sheet of filter material 222 is unshaded. It will be appreciated that in addition to attachment of the sheets 221, 222, 223 to the blocks 211, 212, 213 at the ends of the sheets further fixings, for example along the upper edges of the sheets 221, 222 may be desirable in order to prevent the sheets from slipping downwardly.

The embodiment 200 of Figs. 32 and 33 thus provides a self-supporting silt barrier which does not need posts which may be easily damaged, or even hazardous. The embodiment 200 may be driven over by vehicles such as may be used on construction sites without substantial damage and, because of the resilient nature of the material used to form the blocks 211, 212, 213, will return to

substantially its original height with its function substantially unimpaired. The embodiment 200 thus

provides important benefits over typical conventional silt barriers .

Under certain circumstances it may be considered by those providing silt barriers for use on a particular site that the benefits provided by the silt barriers described above are not required over the entire length of a long silt barrier. For example parts of the perimeter of a site may be inaccessible or positioned such that they may never be traversed by a vehicle. One envisaged embodiment of a silt barrier, as illustrated in Fig. 34, may

therefore comprise one or lengths of conventional silt barrier 300 comprising posts 310 supporting a sheet filter material 312 and one or more lengths of a silt barrier in accordance with an embodiment of the present invention, such as, for example, embodiment 200. In the event the conventional silt barrier 300 is considered to be more economical or more convenient to transport than

embodiments of silt barriers according to the present disclosure, this arrangement could enable the economy and portability of the conventional silt barrier to be

utilized whilst still allowing the benefits of silt barriers in accordance with the present disclosure to be realized where they are most needed (for example in easily accessible and/or high traffic areas) .

It will be understood to persons skilled in the art of the invention that many modifications may be made without departing from the spirit and scope of the

invention.

It is to be understood that, if any prior art publication is referred to herein, such reference does not constitute an admission that the publication forms a part of the common general knowledge in the art, in Australia or in any other country.

In the claims which follow and in the preceding description of the invention, except where the context requires otherwise due to express language or necessary implication, the word "comprise" or variations such as "comprises" or "comprising" is used in an inclusive sense, i.e. to specify the presence of the stated features but not to preclude the presence or addition of further features in various embodiments of the invention.