CA2144361A1 - Storm water drainage system - Google Patents

Abstract

A storm water drainage system comprising catch basins, manholes and storm sewer mains is improved by a surrounding trench filled with porous material to form a reservoir. Perforated pipes extending between adjacent manholes permit some of the storm water runoff during peak runoff periods to flow from the perforated pipes into the porous reservoir and to flow out of the reservoir and into the drainage system during other times.

Description

~L 8'r0RM IrAq~ER D~T-a"" 8YJ3TEM
This invention relates to illlyI ~v~ -nts in urban 3 drainage systems. In particular, it relates to; r-xvcd ~. handling of storm water runoff (in conjunction with storm sewer systems).
6 The increasing urbanization of modern societies, and 7 the increased concern for water quality as an environmental 8 issue, have led to increasing concerns for the manner in which g storm water runoff is controlled.
lo Historically, rain water fell on sand, gravel, or 11 soil covered with vegetation would seep into the ground or run off in a controlled manner except in rare circumstances where 13 exposed soil or exceptionally heavy storms have caused 1~ flooding or erosion. Ilowever, in cities, the large areas covered by b-]i l~inq~, parking lots, roadways, and other 16 barriers to natural drainage have resulted in drainage 17 problems which are exaggerated and concentrated. 'rO avoid exce6sive runoff or flooding, urban communities are designed with a network of catch basins and underground sewer mains 3 designed to receive large amounts of rainfall and carry it off . to a downstream destination.
Nevertheless, occasionally large amounts of water C falls in a very short time during severe storms so that even a well designed system is inadequate to handle the runoff.
8 The result is that the storm mains are f looded and the runof f 9 carries away soil and chemicals associated with urban and industrial centres creating a surge of polluted water which overwhelms treatment facilities and adversely affects natural 12 streams and lakes, etc.
13 For instance, a typical "two year" storm sewer main 1~ might be designed to handle the runoff from a storm with a severity which only occurs every two years. An F-nh~n~
16 design to carry any possible storm would be unjustifiably 17 expensive and space cnncl~min~. Therefore, it has to be acknowledged that occasionally 5torms will occur which Z overf low the system.
3 Various methods have been devised to deal with such 4 inrLe~u~l.L but large and damaging runoffs. One method is to provide relatively deep channels with outwardly inclined sides 6 so that they can ~ te a very large f low of water at 7 their u~ banks. However, these create hazards and 8 barriers to street traf f ic requiring bridges, etc .
g Another method is to provide large ponds or reservoirs capable of receiving and temporarily storing storm 1.~ water runoff until it can be handled by the sewer mains, but these require the dedication of large areas of open space 13 which are expensive or unavailable in urban area6.
1~ Some systems, 6uch as proposed in U. S. Patent lS 4,457,646, provide underground reservoirs covered by 16 playgrounds or fields, but these require expensive structural 17 designs.

~ 2144361 ~, It is theref ore the purpose of this invention to create a means to handle exce6sive storm water runoff 3 efficiently and ineYr~n~ively.
It is also the purpose of this invention to provide a r- ' -ni~-~ for modifying and handling the rate of water flow 6 from surface runoff so that flooding and pollution are 7 minimized.
8 It is also the purpose of this invention to provide g an ~nh~nc~.cl means for h~n~ll ing storm water runoff in conjunction with existing storm sewer mains without requiring ~1 additional land or facilities.
~hese objects and other advantages are sought to be ~,3 achieved by means of the present invention in which a storm lJ. water drainage system having a plurality or manholes connected by storm sewer mains and having catch basins to conduct 16 surface water runoff to the drainage system includes the 17 i, .,v. ~ which comprises an excavation incorporating at ~ 2144361 lea6t a portion of the storm water drainage system and said excavation i8 f illed at least in part by a porous material 3 forming a reservoir. The i, I.,v~ -nt also comprises perforated pipes extending between adjacent manholes in contact with the porous re6ervoir material so that some of the 6 water collected by the drainage system may be allowed to drain 7 into the porosity of the reservoir during peak runoff and may 8 be allowed to drain back out of the reservoir and into the 9 drainage system at other times.
The system may be made more ef f icient if the 11 perforated pipes are wrapped in filter cloth to prevent solids 12 in the storm water f rom plugging the system .
13 The system may also function more effectively if the 14 porous reservoir material in the excavation is also surrounded, at least in part, by filter cloth to keep fine 16 soil material out of the reservoir.
17 In one ~-mho~ the perforated pipe extends 21~361 between adjacent manholes below the level of the 5torm sewer main, . ' ~~'~o~ in the porous reservoir material, and has a 3 plug ad~acent the downstream end thereof, preferably upstream from at least one perforation.
In a second ^-' 'ir-~lt a first perforated pipe 6 extends between adjacent manholes in the excavation above the 7 level of the storm sewer main and has plugs adjacent the 8 upstream and downstream ends thereof while a second perforated g pipe extends only from one manhole in an upstream direction only part of the way to the next adjacent upstream manhole and 11 is: ' ~dod in the porous material beneath the level of the storm sewer and has a plug adjacent the upstream end thereof.
13 In this embodiment the catch basin preferably has a first lateral drain exiting at a lower elevation and connecting to the first upper perforated pipe and has a second lateral drain 16 at a higher elevation connecting directly to the storm sewer 17 main.

` 2144361 The invention may be better understood by a 2 description of one or two: '~~';-~nts thereof with reference 3 to the attached drawings in which:

4 Figure 1 is a pelD~e~;Live view of a storm water drainage system in accordance with the 6 present invention;
7 Figure 2 is a longitudinal section of the system shoWn in Figure 1;
g Figure 3 is a cross-sectional view of the system shown in Figure 1;
l Figure 4 is a perspective view of an alternative ~ P~nho~li t of the present invention;
13 Figure 5 is a longitudinal section of the system 14 shown in Figure 4;
Figure 6 is a cross-sectional view of the system 16 shown in Figure 4.
17 Figure 1 illustrates a typical urban location in ~ 2144361 ~, which re6idential lots border on a street 2 which has catch basins 4 at intervals along the curb side thereof. The catch 3 basins may include devices such as a goss trap or similar 4 devices to restrict the flow of oil or other contaminants into S the system. The catch basins 4 are connected by a lateral 6 pipe 6 to the main storm sewer 8 which has manhole 7 installations 10 at regular intervals along its length.
8 Manhole covers 12 are located at street level and permit 9 access to the system for inspection or maintenance.
lo All of the foregoing is relatively typical of 11 conventional storm sewer systems which are constructed along with and in conjunction with streets, curbs, and sidewalks.
13 In addition, the illustrated embodiment in Figure 1 14 includes a pair of perforated pipes 20 and 22 located beneath the main sewer line 8, both of which are also connected to the 16 manholes lo.
17 The system, including manholes, main storm sewer, ~ 21~381 and perforated pipes are originally constructed in a trench z excavated beneath the eventual level of the street, and after construction, the trench is filled to surround the main and 4 perforated pipes with porous material such as crushed stone 24 S better illustrated in Figures 2 and 3. In addition, the 6 perforated pipes 20 and 22 are wrapped with a filter cloth 26 7 to prevent fine rock or soil from entering the perforations of 8 the pipes 20 and 22.
9 Furthermore, the trench 28 as seen in Figure 3 is lined with a filter cloth before being backfilled with the 11 crushed rock to prevent fine material in the soil 30 from 12 entering the pores of the crushed stone.
As seen in Figure 2, the perforated pipe 20 is 14 provided with a mechanical plug 32 which may be reached from the manhole so that it can be installed, removed, or 16 repositioned.
17 When a storm of unusual severity creates a large ~ 2144361 runoff of surface water, much of it will collect on streets iL where it runs into the catch basins 4 along the curb side of 3 the street. From the catch basins the water will travel along 4 the lateral pipe 6 to the main storm sewer pipe 8 and will f low downstream as indicated by the arrow 14 to the next 6 manhole. In a conventional system the water would continue through each successive line until it reaches the ultimate 8 treatment facility, reservoir, lake, or stream.
g In the present system, however, the water flows from the main into the next manhole and f lows into the two perforated pipes 20 and 22 which are plugged by a mechanical plug 32 near their downstream ends. As a result, the water passes through the pipe perforations and the filter cloth into 1~ the stone-f illed trench where it f ills the void spaces and ultimately seeps into the ~UL ' ~ullding native soil.
lC When the amount of runof f exceeds the capacity of 17 the perforated pipes, the water level will backup in the . ~
~1 perforated pipes toward the upstraam manhole where it will ;~ overflow via the conventional storm sewer pipe 8 and will flow 3 to the next downstream manhole where the proces8 i8 repeated.
Thus, the de5ign of the present invention provides means by which storm water runof f may be absorbed into the 6 void spaces of the crushed stone in the trench, and some of it 7 will seep into the iuLLuullding soil. As the capacity of the 8 soil and the crushed stone to absorb water i8 used up, the 9 f low is passed down to the next section of the sewer system in 1.0 repeated sequence. Therefore, instead of the system having to handle the volume of runoff within the manholes and the sewer ~ 2 mains 8, a large volume is a_ - 'Ated within the crushed 13 stone and ~uLLuullding soil.
1~ If the ---h Ini~AAl plug 32 is positioned upstream from one or more of the lowermost perforations in the pipe 20, lC it will be appreciated that the water collected in the porous 17 reservoir in the trench and surrounding soil can, after the ~ storm is over, be gradually drained from the trench into the 2 lower ends of the perforated pipe 20 to the manhole and 3 eventually back through the system so that the accumulated storm water runoff is slowly dissipated leaving the stone-filled trench reservoir ready to receive the runoff from the C next storm.
7 Figure 4 shows an alternative ~mh~ t of the 8 invention in connection with a conventional storm sewer system 9 in which the roadway 2, the catch basins 4, the manholes 10, the storm sewer mains 8, are all similar to those illustrated 11 in Figure 1.
~owever, the catch basins 4 are provided with a pair 13 of lateral pipes. Lateral pipe 46 exits the catch basin from 1~ a lower position and enters a perforated pipe 50 positioned above the level of the main storm sewer 8. A second lateral 16 pipe 48 exits from a higher position in the catch basins and 17 drains directly into the main storm sewer 8. The perforated 21~4361 pipe 50 extends between adjacent manholes 10 and is wrapped in a filter cloth similar to the arrangement in Figure 1. In addition, lower perforated pipes 52 and 54 also covered with filter cloth are positioned below the main storm 6ewer and extend in the upstream direction from the manhole 6 approximately halfway to the next upstream manhole where they 7 are closed by a cap 56 at the upstream end. As in Figure 1 8 the system of Figure 4 is constructed in a trench which is backfilled with crushed stone as illustrated in Figures 5 and 6.
As seen in Figure 5, the upper perforated pipe 50 is 12 provided with a mechanical plug 58 near each end.
~,3 In the embodiments illustrated in Figures 4, 5, and 14 6, storm water is collected in the catch basin 4 and the lS earliest runoff is transported by the lateral pipe 46 to the 16 upper perforated pipe 50, which is plugged at both ends, so 17 that it passes out through the perforations and into the void ` 2~361 1~
space of the crushed stone 24. It will gradually percolate . down through the crushed stone to the lower perforated pipes 3 52 and 54 which carry the flow to the next downstream manhole.
Since the lower perforated pipes do not extend to the next upstream manhole, the water must rise in the manhole until it eventually overflows into the main storm sewer 8 and is 7 carried of f .
8 Thu6, by this system the runoff is delayed by the g time it takes to percolate through the crushed stone from the upper perforated pipe 50 to the lower perforated pipes 52 and 1~ 54 but the accumulation in the crushed stone and surrounding lZ soil is not as great, and the delay is not as significant as the system illustrated in Figure l.
It should be appreciated that the amount of delay built into the system can be shortened by lengthening the 16 lower pipes 52 and 54, or the delay can be extended by 17 shortening those pipes which control the rate of f low .

214~361 The catch basin arrangement shown in Figure 6 does not permit the usual traps but the initial runoff will travel 3 the lateral pipe 46 to the perforated pipe 50 and se~p through the crushed stone. As resistance to this flow builds up, the water level will rise in the catch basin and eventually will 6 overflow into the lateral pipe 48 which leads directly to the 7 main storm sewer 8. By this arrangement the initial flow, 8 which carries the most pollutants, is diverted through the g crushed stone.
Although the present invention is not restricted to specific dimension or specification, it is the inventors' experience that the ~mho~ t illustrated in Figure 1 is 13 workable for the treatment of 15 millimetre storm events at 1~ three day intervals under existing water quality guidelines if the perforated pipes are standard 35 PVC gravity sewer pipes 16 of 200 m~llir Lr_ diameter with 12.5 millir tre diameter 17 holes, and wrapped with geotextile material with an effective lC
opening size in the range of SO to lSO microns. The trench which should be in the order of 2 to 6 meters square in cross-3 section is filled with crushed stone of a particle size from SO to 100 microns.
Thus, by means of the present invention, a system is 6 provided underground within the space occupied by the 7 conventional storm sewer system which will provide an immediate reservoir volume to absorb the initial runoff, will g provide for seepage of some of the runoff into the surrounding soil, and will effectively slow the rate of flow of surface water f rom a severe storm .
Furthermore, the iulyL~/V- -~ts may be installed at 13 the time of initial installation without substantial 1~ additional cost, or can be installed at some future date, if lS n~c~gg;~ry.
16 It is believed that particles in the runoff water 17 will be removed, bacteria will die off in the soil environment, and fertilizers and other nutrients will likely 2 be taken up by trees in the surrounding soil. Thus, ground 3 water will be recharged and stream flows ~nh~nced with cool water at a relatively constant rate.
It will, of course, be realized that numerous 6 variations and modifications of the illustrated embodiment may 7 be employed without departing from the inventive concept 8 herein.

Claims (7)

1. In a storm water drainage system having a plurality of manholes, storm sewer mains connecting between adjacent manholes, and catch basins to collect surface water runoff and deliver it to the storm sewer mains, the improvement comprising:
- an excavation surrounding at least a part of said storm water drainage system, said excavation being filled with a porous material;
- at least one perforated pipe extending between adjacent manholes in contact with said porous material in said excavation whereby storm water runoff may pass from said perforated pipes in said porous material and may drain from said porous material into said perforated pipes to return to said storm water drainage system.

2. A system as claimed in claim 1 in which said perforated pipes are surrounded by a filter cloth.

3. A system as claimed in claims 1 and 2 ln which said porous material in said excavation is at least partially surrounded by a filter cloth.

4. A system as claimed in claims 1, 2 and 3 in which said perforated pipe extends between adjacent manholes and is embedded within said porous material at a level beneath the level of said storm sewer main and has a plug located adjacent downhill end of said perforated pipe.

5. A system as claimed in claim 4 in which said plug is located upstream from at least one perforation in said perforated pipe.

6. A system as claimed in claims 1, 2, and 3 in which a first perforated pipe extends between adjacent manholes, above the level of said storm sewer main and has plugs located near the upstream and downstream ends thereof, and a second perforated pipe extending from one manhole part of the distance towards the adjacent upstream manhole, located below the level of said storm sewer main and having a plug adjacent the upstream end of said perforated pipe.

7. A system as claimed in claim 6 in which said catch basin has a lower outlet lateral drain connecting to said upper first perforated pipe and a higher outlet lateral drain connecting to said storm sewer main.