Such surface water systems for transport of surface water, i.e.

mainly rain water, but also melted snow, to some watercourse are present in most cities. There is a very big risk for that the surface water system will overflow in the downstreams regions thereof due to the continuously increasing flow in the down- stream direction of the surface water conduit and therefor the level of the surface water in cities located within areas at times exposed for heavy rains or cloudbursts, especially in larger cit- ies within such areas, where a proportionately large number of surface water receiving units with a correspondingly large "collection area" are respectively connected to proportionately long surface water conduits. This problem is especially serious in cities where new districts have been built maybe kilometres away from said outlets and consequently surface water receiving units have been added gradually to the surface water system.

The problem is that surface water gutters 1 located down- streams overflow and water penetrates into the basements of

buildings 2 located there, which is illustrated in fig. 1, which schematically shows an earlier known surface water system of the type defined in the introduction. This results in serious damages on buildings and similar as well as in serious damages on the ground and foundation by means of erosion.

SUMMARY OF THE INVENTION The object of the present invention is to provide an arrangement of the type defined in the introduction, which enables to reduce the above mentioned disadvantages of such arrangements ac- cording to prior art to a great extent.

This object is achieved according to the invention by means of providing such an arrangement with means arranged upstreams in the system at a considerable distance from said outlet in or- der to form flow resistance against surface water there flowing towards the outlet for increasing the level of the surface water in the system upstreams thereof.

The level of the surface water in parts of the surface water sys- tem located upstreams will rise by means of in this way in- creasing the flow resistance in the surface water system up- streams due to the slower flow, so that parts of the surface wa- ter system, which earlier also at cloudburst were nearly empty or only filled to a small extent, will be filled to a substantially larger extent and the filling of parts of the drain water system located downstreams of the flow resistance will take place slower and in this way may overflows be avoided downstreams close to the outlet of the surface water system. You could say that the parts of the surface water system located upstreams will in this way take care of some of the water, which otherwise would have filled and overflowed the surface water system further down, and this takes accordingly place by that the velocity of the flow to the downstreams located parts is being reduced.

According to a preferred embodiment of the invention the ar- rangement comprises members for adjusting the size of the flow resistance of said means. The flow resistance may by means of the presence of such members be adapted to the prevailing conditions and for example be made small when small amounts of surface water are being received by the system per unit time in order to keep the water level of parts located upstreams on a low level while waiting for heavier rains and the flow resistance is being considerably increased when there is a need therefor at presence of such heavier rain in order to prevent overflows fur- ther down in the surface water system.

According to another preferred embodiment of the invention said means are arranged at different distances in the flow direction from said outlet, and said means are forming a flow resistance against the surface water, said flow resistance increasing with longer distance from said outlet. It is advantageous that in this way create the largest flow resistance where the water level without presence of said means would have been lowest in order to in this way utilise the water receiving and water housing capacity, which the surface water system provides to an opti- mum.

According to another preferred embodiment of the invention at least some of said means are arranged in the surface water conduit for forming flow resistance there. Such an arrangement of the means forms an easy and effective way of achieving said increased flow resistance in the surface water system, but it should be noted that the invention such as it is described in the independent patent claim also covers the possibility of arranging similar means in the surface water receiving units or in any short connection conduit between such a unit and the surface water conduit itself.

According to another preferred embodiment of the invention said means are arranged in the surface water conduit closely down-

streams of a surface water receiving unit each. Such an ar- rangement of these means enables a decrease of the velocity of the surface water flow in connection with said unit, so that the water level in this unit will rise in this way and this unit will hence be able to temporarily take care of an increased part of the surface water in the surface water system.

According to another preferred embodiment of the invention the arrangement comprises at least one surface water receiving unit in the form of a surface water gutter, a main drain water conduit extending in the vicinity of the surface water conduit at said gutter for transport of drain water from buildings, and a connec- tion conduit arranged for allowing flow communication between the gutter and the main drain water conduit through an overflow in the gutter. The risk for an overflow in the surface water sys- tem will be further reduced by means of this arrangement, since it provides a possibility of transporting a part of the surface wa- ter in said main drain water conduit before it rises to such a high level in said gutter that an overflow takes place.

According to another preferred embodiment of the invention, which is a further development of the last mentioned embodi- ment, the arrangement comprises a first valve member arranged in said connection conduit and adapted to be able to open and close respectively the flow communication between the gutter and the main drain water conduit. Such a valve member is ad- vantageous in the cases where the main drain water conduit temporarily is not suited for receival of surface water for some reason, for example due to that it is drained for renovation work or due to that drain water of a specific contamination type tem- porarily is being transported in the main drain water conduit, which drain water type is not desirable to be mixed with the surface water.

According to yet another preferred embodiment of the invention, the arrangement comprises a second valve member arranged in

a connection conduit between the gutter and the surface water conduit and adapted to be able to close and open the flow com- munication between the gutter and the surface water conduit, a third valve member arranged in the main drain water conduit downstreams of the gutter and adapted to be able to open and close the flow communication between portions of the main drain water conduit upstreams and downstreams thereof in the main drain water conduit, and a device arranged to pump water in the main drain water conduit through said connection conduit to the gutter when the second and third valve members are closed in order to form a fire dam therein for fire-fighting pur- poses. Another opportunity is in this way obtained for providing water for fire-fighting purposes, which may show to be extremely valuable in places where fires otherwise may lead to that build- ings are being burnt down due to that the access of water for fire-fighting purposes is limited or non-existent.

According to a preferred further development of the last men- tioned embodiment the arrangement comprises a conduit ex- tending up from the surface water gutter as well as a pump for pumping water from the gutter for fire-fighting purposes. The surface water gutter with the water existing therein may advan- tageously be utilised for fire-fighting by the presence of this con- duit and pump.

Further advantages and advantageous characteristics of the in- vention are disclosed in the following description.

BRIEF DESCRIPTION OF THE DRAWINGS With reference to the appended drawings, below follows a spe- cific description of a preferred embodiment of the invention cited as an example. In the drawings: Fig. 1 is a schematical view of an arrangement in a surface wa- ter system according to prior art,

Fig.2 is a schematical view of an arrangement in a surface water system according to a preferred embodiment of the in- vention, Fig. 3 is a partly cut view of the surface water system on a level with a surface water gutter transversely in relation to the surface water conduit of the system according to fig. 2, Fig. 4 is a very simplified perspective view of a part of the ar- rangement according to the invention on a level with a surface water gutter, and Fig. 5 is a view corresponding to fig. 3 and illustrating how a surface water gutter of the surface water system may be utilised for fire-fighting purposes.

DETAILED DESCRIPTION OF A PREFERRED EMBODIMENT OF THE INVENTION An arrangement in a surface water system according to a pre- ferred embodiment of the invention is very schematically illus- trated in fig. 2. The surface water system has conventionally a plurality of surface water receiving units in the form of surface water gutters 1, which are arranged for collecting rain water and melted snow from adjacent ground areas, which is indicated by the arrows 3. The gutters 1 are arranged to discharge surface water into a surface water conduit 4 in common in places along said conduit at different distances from an outlet 6 located at a downstream end 5 of the surface water conduit, at which the surface water conduit 4 is arranged to deliver the surface water in the see, a river or similar. The surface water conduit is ar- ranged to utilise the gravity for transport of the surface water to the outlet, which means that it is inciined towards the outlet.

Means 7 are arranged in the surface water conduit 4 close downstreams of the different gutters 1 for forming a flow resis- tance against surface water flowing towards the outlet there in order to increase the level of the surface water in the system upstreams of itself. These means are for this purpose preferably formed to form a flow resistance against the surface water, which increases with longer distance from the outlet 6, which will lead to that the means located further upstreams have the possibility to rise the level of the surface water flowing there to substantially the same extent as the means located further downstreams despite that the amount of water arriving to the last mentioned means is substantially larger. A means would for example be able to throttle the flow with 10%, the means up- streams thereof with 20%, the next with 30% and so on.

It will in the following text also be referred to fig. 3 and 4. Said means comprise a member 8 for adjusting the size of the flow resistance, and it is in fig. 3 illustrated how this adjusting mem- ber may obtain different degrees of throttling of the surface wa- ter conduit 4. It is in fig. 3 illustrated how at least one surface water gutter of the surface water system is connected to a main drain water conduit 10 for transport of drain water from buildings via a connection conduit 9, said main drain water conduit ex- tending in the vicinity of the surface water conduit at said gutter.

The connection conduit 9 is arranged to allow flow communica- tion between the gutter and the main drain water conduit via an overflow 11 in the gutter 1. The arrangement has further a schematically shown first valve member 12 arranged in said connection conduit 9 and adapted to be able to open and close respectively the flow communication between the gutter and the main drain water conduit. It is possible to utilise the main drain water conduit for receival and transport of surface water for pre- venting overflows at heavy rains due to the presence of said connection conduit when the first valve member is open. Hence, the drain water system is preferably provided with means pre- venting transport of drain water in itself during utilisation thereof

for surface water transport, or at least preventing transport of drain water contaminated to a high degree therein in such situations, wherein the main drain water conduit is a part of the drain water system. It is likely to close the connection conduit via the first valve member 12 if this could not be avoided.

A second valve member 13 is further only illustrated in fig. 5 and arranged in a connection conduit 14 between the surface water gutter 1 and the surface water conduit 4, said valve member being adapted to be able to close and open the flow communi- cation between the gutter and the surface water conduit. A third valve member 15 is arranged in the main drain water conduit downstreams of the gutter adapted to be able to open and close the flow communication between portions of the main drain wa- ter conduit upstreams and downstreams thereof in the main drain water conduit. The arrangement has also a device ar- ranged to pump water in the main drain water conduit through said connection conduit 9 to the gutter when the second and third valve members 13, 15 are closed in order to form a fire dam therein for fire-fighting purposes, which corresponds to the position in fig. 5, said device not being illustrated in the draw- ings. Such a utilisation of the drain water system and the sur- face water system is illustrated in fig. 5, and it is there also shown how a conduit 16 extending up from the surface water gutter as well as a pump 17 may be arranged for pumping water from the gutter for said purposes. This possibility for forming a fire dam is not necessarily needed at each gutter in the surface water system, but it could for example be provided in one place for each district.

The invention is of course not in any way limited to the above described preferred embodiment, but a number of modifications thereof should be apparent for a man skilled in the art without leaving the inventive idea such it is described in the attached patent claims.

It is for example possible that said means forming the flow re- sistance are being arranged only a proportionally long way up- streams in the surface water system or at least closer there than further downstreams, and it is of course normally no use to form any flow resistance downstreams of the surface water gutter lo- cated closest to the outlet, even though a means for this pur- pose is shown there in fig. 2. It is also within the scope of the invention to only arrange one single such means in the surface water system. The meaning of the expression "considerable distance" is however that when one single such means is pres- ent, it is not located directly at the outlet.

It is also not necessary that there are any overflows in the gut- ters to any main drain water conduit, but if so it can just as well be arranged for only certain chosen gutters, preferably at least in the gutters where the risk is largest for an overflow, i.e. fur- thest downstream in the system, even if this forming also is ad- vantageous further upstreams in the surface water system, in the first place for fire-fighting purposes.