Waterways often require stabilization to enable desired flow conditions to be maintained. Typically stabilization may be required in conditions where the waterway passes through erodible bed material. Stabilization of a waterway could be associated with the diversion of a watercourse through material less durable than that in the waterway's original location, or along an alignment which is steeper than that associated with the waterway's original location. Stabilization may also be required when discharges to be conveyed by the watercourse have been increased.

Waterway stabilization can be an extremely expensive exercise if it is undertaken in accordance with acceptable standards. A technique that may be used to stabilize a watercourse includes one or a cascade of water drops which produce relatively high flow velocities at the bed of the waterway immediately downstream of each water drop. At this point severe scour and erosion can result in instability of the waterway. Thus stabilization of each water drop is necessary to ensure stabilization of an entire cascade structure.

At present the measures taken for this purpose are varied and include the use of rock filled wire baskets to form both the wall and the lower bed. While this method is cost effective and flexible enabling it to tolerate some foundation settlement, the wire baskets are prone to distortion and are subject to corrosion and erosion. Thus they may offer only short term stabilization of the waterway. Such structures may also become unstable under high flow velocities.

Reinforced concrete slabs are also used. However while they are durable, they are relatively expensive to install and erosion of the earth supporting the slabs can cause the slabs to be displaced from their operative positions. Driven steel sheet piles and concrete posts are also utilised to form water drops. However the associated difficulty of stabilizing the downstream bed adjacent the water drop remains.

This invention aims to alleviate at least one of the above disadvantages and/or to provide improvements in water drop structures.

In one aspect this invention resides broadly in a waterfall assembly for stabilizing a substrate including a baffle located on a lower bed of the substrate and spaced from a riser face of the substrate and a plurality of dividers extending from said baffle to the riser face whereby the lower bed of the substrate is stablized against displacement by water flow.

The baffle or baffles may be retained by being pinned to the bed rock or the subsoil or they may be secured to the wall forming the water drop. Alternatively the baffles may be of sufficient weight so as to be retained in a placed position on the foundation. The baffles may also be configured to induce hydraulic forces to retain the baffles in position or assist in their retention. The baffles may be retained by a combination of the above variations.

The baffles may be secured to one another in an articulated manner so as to generally conform with the upper surface of the bed rock or they may be arranged independent of one another.

The water fall assembly may be used for short term stabilization or for long term stabilization. Suitably each baffle is formed as a concrete block that incorporates a divider in the form of a longitudinal spine extending along the rock bed and a baffle in the form of an enlarged head located downstream of the water drop wall and suitably disposed at the normal-flow drop zone, or adjacent to or downstream of the normal-flow drop zone. The heads of adjacent baffles may be spaced apart so as to provide a narrow flow-way therebetween or they may have conforming lateral extremities so that the heads abut or lie adjacent one another to form a substantially continuous shallow weir across the rock bed downstream of the wall forming the drop.

The head may be formed as lateral extensions to the longitudinal spine. The baffles may generally be L-shaped or T-shaped so as to form the required lateral extensions or the baffles may have rounded head parts.

In one form of the invention each baffle is loosely associated with and suitably retained by a respective complementary anchor that extends into the material behind the wall and is configured for retention thereby. Suitably the anchors also provide location for an upstream weir across which water flows over the water drop. The weir may be formed as a continuous member or an articulated member or

from weir blocks which are arranged end to end behind the anchor members to form the upstream weir.

The anchors may also have lateral extensions. Preferably the anchors are anchors blocks which have substantially the same lateral extent as do the heads of the baffles and weir blocks which are arranged in-line behind the the anchor blocks to form the upstream weir so that all the parts may be assembled in side by side abutting relationship with rock backfill to form a continuous water drop structure across a rock fill bed.

The present invention also resides in a method for stablizing the lower bed of a substrate of water drop structure including the steps of locating a baffle on a lower bed of the substrate spaced apart from a riser face of the substrate and locating a plurality of dividers extending from said baffle to the riser face and retaining said baffle and said plurality of dividers substantially in position whereby the lower bed of the substrate is stablised against displacement by water flow.

In a further aspect, this invention resides in a water fall assembly comprising a plurality of block groups in side by side alignment across a watercourse, each block group including a weir block, a baffle block and an anchor block, wherein :- each baffle block includes a longitudinal spine which is arranged in-line with the watercourse and an enlarged head which is located downstream of the drop wall and suitably at or adjacent the normal-flow drop zone each weir block is arranged across the upper edge of the water drop to form a weir crest, and each anchor bock contains an anchoring portion which is embedded in the upstream watercourse fill or foundation material and a locating portion which operatively locates the weir block and the baffle blocks on the watercourse.

The present invention further resides in a set of blocks for forming a water fall assembly including block groups for side by side alignment across a watercourse wherein each block group includes a weir block, a baffle block and an anchor block wherein: each baffle block includes a longitudinal spine for alignment in-line with the watercourse and an enlarged head for location downstream of the drop wall and suitably at or adjacent the normal-flow drop zone; each weir block forms a weir crest, and

each anchor block contains an anchoring portion for embedding in upstream watercourse fill or foundation material and a locating portion for locating the weir block and the baffle blocks on the watercourse.

The anchoring blocks may be fully concealed in the upstream fill or foundation material and the locating portions of the anchoring bock may be adapted to interlock with one or adjacent ones of the weir blocks and baffle blocks. Alternatively the anchoring blocks may provide abutments for holding the weir blocks and baffle blocks in position. The anchoring blocks may include post portions which lie over the drop face of the water drop and the posts may extend vertically beyond the weir blocks and the baffle blocks to form abutments which retain the weir blocks and the baffle blocks in position.

Suitably the head of the baffle blocks are arranged in side by side relationship to cover a significant portion of the drop zone whereby much of the down flow over the wall impinges against the head parts. A significant portion of the flow may also pass through any rock fill material on which or with which the drop structure is constructed.

The post portions may extend above the weir blocks so as to form low castellations which split low flows into streams over the drop wall. These streams may be directed either partially or fully onto a spine portion of the baffle blocks so as to minimise disturbance to the lower bed of the substrate therebelow.

In yet a further aspect, this invention resides in a method of forming a water drop utilising the apparatus variously defined above, and including :- excavating a waterway substantially in conformity with the proposed waterway floor ; lining the excavation; arranging a plurality of anchor blocks on the lower bed of the substrate in side by side relationship across the watercourse; forming a rock filled wall structure about the anchor blocks ; arranging baffle blocks on the lower bed of the substrate with their head parts downstream of the wall structure; anchoring the baffle blocks by the anchor blocks; arranging weir blocks across the upper edge of the drop structure to form a substantially continuous weir crest, and

anchoring the weir blocks by the anchor blocks.

Suitably the method also includes forming the intermediate finished waterway between successive sequences of blocks with a rock protected fill. The excavation may be lined with a layer or layers of graded rock material or synthetic alternatives.

The anchor blocks suitably include an anchoring part having lateral extensions which may be encased by rocks or upstream fill material for anchoring purposes and an upstanding face part behind which rock fill may be placed to form the drop structure.

Suitably the waterway is excavated to a greater dept beneath the drop zone and the protective bed over the deeper excavation is formed from either a single or multiple layers of graded rock with relatively large rock gradings in the upper layer.

In order that this invention may be more readily understood and put into practical effect, reference will now be made to the accompanying drawings which illustrate a typical embodiment of the invention, wherein: FIG. 1 illustrates normal operation of a water drop structure according to the described embodiment; FIG. 2 illustrates the structure of the water drop structure and associated retaining walls of Fig. 1; FIG. 3 illustrates low flow operation of a water drop structure according to the described embodiment; FIG. 4 is a cross-sectional view showing the relationship between the block members and the rock fill according to the described embodiment; FIG. 5 is a plan view of a cascaded water course; FIG. 6 is a typical cross sectional view through the line 5-5 of Fig. 4; FIGS. 7A and 7B are plan and end views of a typical weir block ; FIGS. 8A and 8B are plan and side views of a typical baffle block ; FIGS. 9A and 9B are plan and side views of a typical anchor block ; FIG. 10 is a plan view of a water drop structure; FIG. 11 is a plan view showing the end portion of a water drop structure and a retaining wall ;

FIG. 12 is a plan view of a cascade having a number of water fall assemblies according to the present invention; FIG. 13 is a detailed view of the first waterfall assembly shown in Figure 12; FIG. 14 is a cross sectional view of section O from Figure 13; FIG. 15 is a cross sectional view of section N from Figure 13; FIG. 16 is a cross sectional view of the water fall assembly in the direction of flow of the water in Figure 13.

FIG. 17 illustrates the structure of the guide banks and the water falls.

A typical cascade able to cope with a flood discharge in the order of 390 cubic metres per second flow along a waterway with a grade of 10° may have a cascade length of about 200metres with a 1 00metre wide x 1 1/2metre high water drop spaced every 15metres along the cascade.

Such a water course would normally flow across each water drop 10 as illustrated in Fig. 1 which provides a substantial dissipation of flow energy without disruption of the rock bed therebelow. As illustrated the stabilized water course 11 has a rock fill base 12 formed from relatively small angular rock having a maximum section of about 300mm and larger rock having a maximum section of about 450mm immediately downstream of the drop wall 14.

In this embodiment each water drop 10 has'H'shaped baffle blocks 15 laid directly on the larger rock fill 13 at the base of the drop wall 14 and with their outer transverse members 18 arranged in end to end abutting relationship across the watercourse. The inner transverse members 19 are connected thereto by a spine 17 are shorter and are located behind the lower ends 21 of the upright posts 22 of anchor blocks 20.

Each anchor block 20 has a stem 24 which typically extends rearwardly and downwardly through the rock fill 25 behind the post 22. Each stem 24 has an inner transverse abutment 28 embedded within the rock fill to secure the anchor blocks 20 in position.

Weir blocks 30 are supported behind the upper ends of the posts 22 on the rock fill 25 behind the posts 22 and with their upper faces 32 at the upper level 31 of the rock fill 25 which forms the bed of the watercourse immediately upstream of the drop wall 14.

Thus it will be seen that block groups each comprising a baffle block 15, a weir block 30 and an anchor block 20, may be simply assembled in side by side relationship across a watercourse to form a water drop structure. Further it will be seen that the inner transverse abutment 28 of the anchor block 20 is substantially the same overall width as the head parts 18 of the baffle blocks 15 and the weir block 30 so that they may be simply laid in abutting relationship across a water course to form a relatively straight water drop structure. The ends of the head parts 18 or alternatively the weir blocks 30 and baffle blocks 15 may be laid in a spaced relationship to enable a curved drop structure to be formed.

It will also be seen from Fig. 11 that the weir blocks and the anchor blocks may be used to form a retaining wall 40, such as at the ends of the water drop structure 10.

The present invention alleviates a number of limitations of alternative techniques. It is well suited to application in the mining industry, both for temporary and permanent works. A water drop structure according to this invention enables ready conformance with hydraulic design requirements for a drop structure. When the blocks are laid in an interlocking manner to form the water drop structure they retain the upstream rock fill material and hold rock fill material at the base of the drop in place. In use the assembled blocks reduce general local flow velocities near the bed of the waterway in the high velocity region to the downstream of the drop and thus minimise erosion of the subsoil beneath the lower bed of the substrate of rocks.

This enables the rocks in the drop zone to remain in their placed position Typically the blocks would be pre-cast concrete and may be reinforced. They would be lifted in place during construction and then have rock fill placed about them.

Their dimensions would vary according to hydraulic design requirements that would define the overall geometry of the required single drop or multiple drop cascade.

In the illustrated embodiment stability is achieved using the mass of the rock fill material interlocking with blocks. After the blocks are lifted into position rock fill may simply be dumped into place. accommodate significant foundation movement without comprising the integrity of the structure. The concrete block units are self anchoring and thus a water drop or cascade should generally be economical to construct.

Figure 12 shows a cascade 100 having a number of water fall assemblies 101 down which water may flow in the direction of the arrow 102.

The first waterfall assembly 101a is shown in Figure 13. Figure 13 shows the water fall assembly 101a with guide banks 102 and 103. The construction of the water fall assemblies 101 and the guide banks 102 and 103 are shown in Figures 16, 14 and 15 respectively.

Figure 16 shows the water fall assembly that includes a weir block 105, an anchor block 106 and a baffle block 107.

The guide banks 102 and 103 may be constructed from the weir blocks 105, anchor blocks 106 and baffle blocks 107 where the baffle blocks 107 are disposed laterally to assist in retaining the guide bank in position. The guide banks 102 and 103 are shown in cross section respectively in Figures 14 and 15. In Figure 17 the guide bank 103 may be seen in detail.

It will of course be realised that while the foregoing has been given by way of illustrative example of this invention, all such and other modifications and variations thereto as would be apparent to persons skilled in the art are deemed to fall within the broad scope and ambit of this invention as is herein set forth.