Two level stormwater channel

A method and apparatus for combined conveyance, detention, and infiltration of stormwater runoff.

FIELD OF THE INVENTION

The present invention pertains to stormwater runoff conveyance, detention, and infiltration systems. In particular, the present invention provides a means of integrating detention and infiltration within stormwater channels.

BACKGROUND OF THE INVENTION

Detention of stormwater runoff from urban watersheds followed by either infiltration into the ground and/or treatment for quality improvement and beneficial use is becoming increasingly important as stormwater runoff is now considered a valuable water resource and environmental regulations limit the pollutant loads that storm drains can discharge into natural water bodies.

Current art diverts the stormwater runoff to an off-channel detention storage facility for infiltration into the ground and/or treatment for beneficial use. This often requires extensive civil works for the diversion, conveyance, and detention storage facilities and is contingent upon the availability of sufficient land for these facilities. The undertaking is often extensive and cost-prohibitive. One approach for both stormwater diversion and detention is to use inflatable rubber dams across the channel. This approach has limited detention utility because of limited dam height and the sloping nature of the channel, which only enables utilizing half the channel volume in the reach between the rubber dam and the backwater upstream.

Other than the limited in-channel detention storage created by small dams and gates, current art has largely overlooked the potential utility of the stormwater channel for purposes other than conveyance. This is particularly true for the space below the channel, which is only utilized for as the support for the channel bed and banks above. This is an anomaly in urban areas, which normally utilize the space below most facilities as parking structures, shopping centers, sport facilities, etc. Indeed, the space below the channel bed is the ideal location to house a detention storage facility for stormwater runoff, since conveyance to the facility would occur by gravity and there would not be a need for diversion. Depending on the ground formation and environmental suitability, the space below the channel bed may also be suitable for infiltration in addition to detention. The concept eliminates the need for finding a suitable off-channel site for detention, feasible conveyance alignment alternatives, and suitable diversion scheme and would greatly accelerate stormwater conservation while drastically increasing the stormwater protection capability of existing storm drain, since they would also incorporate sizeable detention storage.

Therefore, there is a need for and great benefits from a means of utilizing the vertical space below stormwater channels for stormwater runoff detention and infiltration. This would greatly enhance the utility of the land occupied by or allocated to stormwater channels and provide an effective and simple tool for stormwater management, conservation, water quality enhancement, while increasing the stormwater protection capacity of existing and future stormwater channels.

SUMMARY OF THE INVENTION

The present invention provides a solution for the above stated need with an apparatus and method that creates basins along and directly beneath the channel bed for stormwater runoff detention and infiltration, while providing a means of safe hydraulic communication between the storm channel and the detention/infiltrations basins below. The invention essentially creates a two-level stormwater channel with the upper level for conveyance and the lower level for detention and infiltration.

The invention consists of deliberately created void spaces along and below the invert of the storm channel bed, in the form of cascading longitudinal detention/infiltration basins. The basins resemble a long row of giant bath tubs buried into the channel bed with level beds and sloping rims flush with the channel invert. Consecutive basins are separated by certain intervals across which there is a step drop in the bed elevation of the downstream basin that equals the drop in the channel bed elevation along the basin length because of the channel slope. Separations may also be located where side channels and other storm drains join the stormwater channel to avoid detention and infiltration of the dry weather flow of such channels. Alternatively, an impervious channel bed may be used at such locations to interrupt the hydraulic communication between the channel and the basin below and/or secondary dry weather flow channels may be used to direct dry weather flows of side channels to the dry weather flow channel of the present invention. Where there is no infiltration, the basins may have slightly sloping beds and consecutive basins may be connected with pipes equipped with flow control devices that are normally closed and opened to enable complete gravity drainage after the event.

The channel bed serves as the interface between the conveyance channel above and the detention/infiltration basins below, over certain widths and lengths of the channel, enabling hydraulic communication between the two facilities. The interface may consist of graded rip rap to maintain channel bed stability and prevent bed erosion during stormwater flows resting on top of carefully graded granular material to serve as filter preventing migration of fines into the detention facility below. Alternatively, geotextiles may be used at the interface for either or both purposes of channel bed stabilization and filtration of stormwater runoff flow into the basins. The channel bed is supported by the basin ceiling, which may take a number of different forms as described below.

In one embodiment the entire void space of the basins created below the channel bed is used for detention using structural support walls. In this case, structural metal or plastic grating, either spanning the walls of the basins on either side or supported by intermediate walls may be used as the ceiling of the basins to support the filter and channel bed protection layer(s) above. In another embodiment, one or several lines of perforated pipe may be laid longitudinally inside the basins over a granular bed, and backfilled with granular material such as crushed stone up to the ceiling level. In this embodiment, the perforated pipes create most of the void space and serve as the main storage elements while the granular material provides structural support, additional voids for storage, and maintains hydraulic communication between the conveyance channel and the interior of the perforated pipe. Here, the filter layer is laid directly over the granular material followed by the channel bed erosion protection layer on top.

If infiltration is required and permitted per local soil conditions and pertinent environmental regulations, then it could be accommodated in both embodiments using a filter layer of either synthetic geotextiles or graded granular material on the wetted perimeter surface of the basins. If the purpose of detention is stormwater conservation for later access, treatment, and use i.e. without infiltration, then the basins would be lined with impervious liner and appropriate means of accessing the water stored in the cascade of basins would be incorporated into the design. Alternatively, non-perforated conduits may be used in lieu of perforated conduits to avoid the need for lining the basins. When using non-perforated conduits, one option is to use perforated risers at intervals to establish hydraulic communication between the channel and the conduit. Alternatively, one may use longitudinal slots along the tops of the conduits, similar to a slotted drain, with funneled inlet from the stream bed for hydraulic communication.

It is an object of the present invention to provide an apparatus and method for increasing the utility of stormwater conveyance channels by enabling them to also function as detention and infiltration facilities.

It is an object of the present invention to provide improved elements and arrangements by apparatus for the purposes described thereof, which is comparable in cost with existing systems, dependable, and fully effective in accomplishing its intended purposes.

DETAILED DESCRIPTION

Referring toFIG. 1there is shown a cross section view of one embodiment of the present invention100during dry weather conditions wherein concrete-box detention basins111with permeable infiltration beds115are accommodated in the ground formation121below a stormwater channel bed101. Infiltration layer115also serves as filter to prevent fines from surrounding ground migrating into basin111in case of flow reversal due to high ground water level. Structural metal or plastic grating114spans the walls of the basins112on either side and serves as the ceiling of the basins to support the filter and pervious channel bed protection layer113above and enable rapid hydraulic communication between the channel101and the basins111below. The stormwater channel may have a low flow channel102that conveys water103during dry weather conditions, which may be kept isolated from the basins111because of water quality concerns.

FIG. 2is the same cross section view of the same embodiment of the present invention100as inFIG. 1during wet weather conditions. Flow in stormwater channel101exceed the capacity of low flow channel102and water103flows into the basins111via pervious bed113over grating114and starts infiltrating into ground formation121. The level of water103only elevates above the channel bed113once basins111are full and stormwater runoff inflow into the channel101exceeds infiltration rate through basin permeable perimeter115.

FIG. 3is the same cross section view of the same embodiment of the present invention100as inFIG. 1shortly after a wet weather event. Channel101is dry except for dry weather flow in low flow channel102, while there is water103captured in detention basins111below invert of channel101, which continues infiltrating into the ground formation121until there is no longer any water103in basins111.

FIG. 4is a longitudinal profile view of the same embodiment of the present invention100as inFIG. 1during dry weather conditions wherein a cascade of separate concrete-box detention basins111with permeable infiltration beds115are accommodated below a stormwater channel bed101. Consecutive basins are separated by certain intervals104across which there is a step drop Y in the bed elevation of the downstream basin that equals the drop in the channel bed elevation along the length of basin111plus separation104, because of the channel slope.

FIG. 5is the same longitudinal profile view of the same embodiment of the present invention as inFIG. 1during wet weather conditions. Level of water103in channel101is above channel invert113and basins111are filled with water103, while there is infiltration across permeable boundary115into ground121.

FIG. 6is the same longitudinal profile view of the same embodiment of the present invention as inFIG. 1shortly after a wet weather event. Level of water103in channel101has dropped to below channel invert113, while basins111contain water103that continues infiltrating into ground121across permeable boundary115.

FIG. 7is a cross section view of another embodiment200of the present invention during dry weather conditions wherein perforated pipes217with crushed stone backfill216in permeable-parameter excavated trenches215are accommodated below a stormwater channel201to serve as detention-infiltration basins211. Infiltration layer215also serves as filter to prevent fines from surrounding ground migrating into basin211in case of flow reversal due to high ground water level. The channel bed213over basins211is highly pervious and may be comprised of rip rap laid over a graded stone filter bed214. The stormwater channel201may have a low flow channel202that conveys water203during dry weather conditions, which may be kept isolated from the basins211because of water quality concerns.

FIG. 8is a frontal perspective view of the same embodiment200of the present invention as inFIG. 7during dry weather conditions showing how the perforated pipes217with crushed stone backfill216in permeable-parameter excavated trenches215may be accommodated below a stormwater channel201to serve as detention-infiltration basins211. Consecutive basins211along channel201are separated over a certain reach204where there is a step drop in the bed elevation of the downstream basin. To avoid capture and infiltration of dry weather flows from side streams205, basin separations204may be located where side stream205enter the main channel201, or the channel bed may be made impervious at such locations.

FIG. 9is a longitudinal perspective view of the same embodiment200of the present invention as inFIG. 7during dry weather conditions showing the separate detention-infiltration basins211comprised of perforated pipes217with crushed stone backfill216in permeable-parameter excavated trenches215accommodated below stormwater channel201bed. Consecutive basins111are separated over certain reach204, which may be located where there is a side channel205entering the main channel201to direct their dry weather flow in the low flow channel202of the main channel. There is a drop in bed elevation of the consecutive basins211to compensate for the bed slope of the stormwater channel201, making the basins deepest at the upstream end. Basin lengths L is set to limit the excavation depth of the basin at upstream end to within manageable and safe levels.

FIG. 10is a cross section view of another embodiment300of the present invention during dry weather conditions wherein interconnected concrete-box detention basins311with impervious liner315are accommodated below a stormwater channel301for stormwater runoff conservation. Structural metal or plastic grating314spans the walls of the basins312on either side and serves as the ceiling of the basins to support the filter and pervious channel bed protection layer313above and enable rapid hydraulic communication between the channel301and the basins311below. The stormwater channel may have a low flow channel302that conveys water303during dry weather conditions, which may be kept isolated from the basins311because of water quality concerns. There may be longitudinal pipes331equipped with normally closed flow control devices (not shown) that connect consecutive basins with different bed elevations along channel301, while adjacent basins with same bed elevation may be connected laterally by level pipes332.

FIG. 11is the same cross section view of the same embodiment300of the present invention as inFIG. 10during wet weather conditions. Flow exceed capacity of low flow channel302and water303flows into the basins311via pervious bed113over grating114and store inside basins311prevented from infiltration into ground321by impervious basin perimeter315. With basins311filling, the level of water303only elevates above the channel bed313to provide sufficient hydraulic head for the flow into the basins and rises to flow in the channel once basins311are full.

FIG. 12is the same cross section view of the same embodiment300of the present invention as inFIG. 10shortly after a wet weather event. Level of water303in channel301has dropped to below channel invert313, while basins311contain water303that remains stored within impervious boundary315until drained via pipes331.

FIG. 13is a longitudinal profile view of the same embodiment300of the present invention as inFIG. 10shortly after a wet weather event wherein a cascade of separate yet interconnected concrete-box detention basins311with impervious liner315are accommodated below a stormwater channel301for stormwater runoff conservation. Longitudinal pipes331equipped with flow control devices333connect consecutive basins311with different bed elevations along channel301, while adjacent basins with same bed elevation may be connected laterally by level pipes332. Water303remains stored within impervious boundary315until drained via pipes331.

FIG. 14is a cross section view of another embodiment400of the present invention during dry weather conditions wherein perforated pipes417with crushed stone backfill416in excavated trenches with impervious-parameter415are accommodated below a stormwater channel bed to serve as detention basins411for stormwater runoff conservation. The channel bed413over basins411is highly pervious and may be comprised of rip rap laid over a graded stone filter bed414. The stormwater channel may have a low flow channel402that conveys water403during dry weather conditions, which may be kept isolated from the basins411because of water quality concerns. There may be longitudinal pipes431equipped with flow control devices (not shown) that connect consecutive basins with different bed elevations along channel401, while adjacent basins with same bed elevation may be connected laterally by level pipes432.

The present invention is susceptible to modifications and variations which may be introduced thereto without departing from the inventive concepts and the object of the invention. Basin configurations other than those shown may be used below the channel and non-perforated conduits may be used in lieu of perforated conduits for stormwater conservation without infiltration to avoid the need for lining the basins. When using non-perforated conduits, the means for hydraulic communication with the channel can take a number different shapes and forms that include perforated risers, slotted soffit, et.

While the present invention has been described in connection with what is considered the most practical and preferred embodiments, it is to be understood that the present invention is not to be limited to the disclosed arrangements, but is intended to cover various arrangements which are included within the spirit and scope of the broadest possible interpretation of the appended claims so as to encompass all modifications and equivalent arrangements which are possible.