Regenerative stormwater conveyance system and method

Abstract

A regenerative stormwater conveyance (RSC) system for treating and dispersing stormwater runoff is disclosed which includes an upstream entry point where water enters the system and an entry pool downstream from the entry point that collects water from the entry point. The RSC system includes one or more shallow aquatic beds that receive water from the entry pool in a serial manner and each of which includes a filtration structure for filtering water from the aquatic bed. Riffle weir grade control structures are positioned between the aquatic beds and transition water overflowing from each upstream aquatic bed to a downstream aquatic bed. Accordingly, collected stormwater runoff traverses the series of aquatic beds and riffle weir grading structures and is treated and safely detained, thus, conveying stormwater to groundwater through infiltration.

Claims

1-15. (canceled)

16. A regenerative stormwater conveyance system comprising: an entry point from which water enters the system; an entry pool operable to collect water entering from the entry point, said entry pool being located at an upstream point in said system; a first aquatic bed having a filtration structure operable to filter water; a first riffle weir grade control structure operable to transition overflow water from said entry pool to said first aquatic bed, wherein said first aquatic bed is lower than said entry pool; a sand base disposed beneath at least the filtration structure and operable to carry filtered water from the filtration structure downstream; and an impervious structure positioned within the sand base and directing water through at least a portion of said sand base.

17. The system of claim 16, further comprising a vertical structure disposed within said first aquatic bed and at least partially embedded within said sand base.

18. The system of claim 17, wherein the vertical structure includes an inverted root wad including a root ban and trunk of a tree.

19. The system of claim 17, wherein the vertical structure is positioned in the center of the aquatic bed.

20. The system of claim 17, wherein the vertical structure is positioned at a downflow side of said aquatic bed.

21. The system of claim 17, wherein the vertical structure is oriented at an angle.

22. The system of claim 17, wherein the vertical structure is at least partially impervious.

23. The system of claim 17, wherein the vertical structure is approximately 24 inches in width.

24. The system of claim 17, wherein the vertical structure is at least 5 feet in length.

25. The system of claim 16, wherein the impervious structure is a clay aquaclude.

26. A regenerative stormwater conveyance system comprising: a plurality of aquatic beds each including a filtration structure operable to filter water from the respective aquatic bed, wherein said filtration structure includes one or more of sand and wood chips; at least one riffle weir grade control structure disposed respectively between each of said plurality of aquatic beds and operable to transfer water overflowing from an upstream aquatic bed to a downstream aquatic bed, wherein the downstream aquatic bed is at a lower grade than the upstream aquatic bed.

27. The system of claim 26, further comprising an impervious structure disposed within a base of at least one of said aquatic beds.

28. The system of claim 27, wherein said impervious structure directs water through porous material.

29. The system of claim 27, wherein said impervious structure is made of clay.

30. A method of designing a regenerative stormwater conveyance (RSC) system, the method comprising: determining the volume of water for storage; mapping out the reach where the RSC will be placed in the landscape; determining the length of the reach from an input point to a discharge point; determining the elevation difference of the reach as the difference between the top of the reach and the bottom of the reach; setting a number of riffle weir grade control structures to be constructed in the system to the elevation difference of the reach; and determining the appropriate size and depth of cobbles.

31. The method of claim 30, further comprising, setting the length of the riffle weir grade control structure(s) to be half the ratio of the length of the reach to the elevation difference of the reach and determining the width and depth of the riffle weir grade control structure(s).

32. The method of constructing a regenerative stormwater conveyance system, the method comprising: determining an entry point from which water enters the system; forming an entry pool operable to collect water entering from the entry point; forming a first aquatic bed lower in elevation than said entry point and including a filtration structure operable to filter water; and forming a first riffle weir grade control structure between said entry point and said first aquatic bed, wherein the filtration structure includes one or more of sand and wood.

33. The method of claim 32, further comprising forming an impervious structure within the first aquatic bed, wherein the impervious structure directs water through porous material.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0024] The object and features of the present invention will become more readily apparent from the following detailed description of the exemplary embodiments taken in conjunction with the accompanying drawings in which:

[0025] FIGS. 1A-1C is a flow diagram showing the steps used to construct a regenerative stormwater conveyance system in accordance with the present invention.

[0026] FIG. 2A is a top view of a regenerative stormwater conveyance system in accordance with one exemplary embodiment of the present invention.

[0027] FIG. 2B is a side view of the regenerative stormwater conveyance system of FIG. 2A in accordance with the present invention.

[0028] FIG. 3 is a side view of the regenerative stormwater conveyance system in accordance with a further embodiment of the present invention.

[0029] FIG. 4 is a close-up side view of an exemplary embodiment of a riffle weir grade control structure used in a regenerative stormwater conveyance system in accordance with the present invention.

[0030] FIG. 5A is a cross section elevation front view of an exemplary embodiment of a riffle weir used in a regenerative stormwater conveyance system in accordance with the present invention.

[0031] FIG. 5B is a cross section elevation back view of an exemplary embodiment of a riffle weir used in a regenerative stormwater conveyance system in accordance with the present invention.

[0032] FIG. 6A is a cross section view of a boulder section of an exemplary embodiment of a riffle weir grade control structure used in a regenerative stormwater conveyance system in accordance with the present invention.

[0033] FIG. 6B is a cross section view of a weir cobble section of an exemplary embodiment of a riffle weir grade control structure used in a regenerative stormwater conveyance system in accordance with the present invention.

[0034] FIG. 7 is a close-up top view of an exemplary embodiment of a riffle weir grade control structure used in a regenerative stormwater conveyance system in accordance with the present invention.

[0035] FIG. 8 is a cross section side view of an exemplary embodiment of a shallow pool used in a regenerative stormwater conveyance system in accordance with the present invention.

[0036] FIG. 9 is a design plan view of an exemplary embodiment of a regenerative stormwater conveyance system in accordance with the present invention.

[0037] FIG. 10 is a cross section side view of an exemplary embodiment of riffle weir grade control structure used in a regenerative stormwater conveyance system in accordance with a further embodiment of the present invention.

DETAILED DESCRIPTION OF EXEMPLARY EMBODIMENTS

[0038] Exemplary embodiments of the present invention are discussed in detail below. While specific configurations are discussed, it should be understood that this is done for illustration purposes only. A person skilled in the relevant art will recognize that other components and configurations may be used without departing from the spirit and scope of the invention.

[0039] Before describing exemplary, non-limiting embodiments in accordance with the present invention, a number of terms are defined to assist the reader. The terms defined are components of a seepage wetland system in accordance with the present invention.

[0040] Primary seepage reservoir—water reservoir designed to irrigate porous media (sand or gravel), spread water out along the outer regions of a project site to detain the first flush of stormwater into a project site at the highest elevation possible on the given site.

[0041] Seepage Reservoirs—Sand berms are placed in appropriate positions in the landscape to capture surface and/or groundwater.

[0042] Sand Berm seepage wetland—A berm of sand designed to contain a seepage reservoir filter and exfiltrate water stored in a seepage reservoir and support plant growth, microbes, algae, fungi and macro-invertebrates.

[0043] Sand berm level spreader—A berm of sand designed to spread stormwater across a broad area to dissipate erosive energies and support plant growth and populations of microbes, algae, fungi and macro-invertebrates.

[0044] Sand seepage bed—A bed of sand is placed in the drainage way (e.g. eroded ravine) and Riffle weirs grade control structures and pools form the new surface topography over top of the sand bed. This allows some water to filter under the surface and exfiltrate as a seep.

[0045] Primary Riffle weir grade control structure—sets water surface elevation in a primary seepage reservoir at the highest grade possible on a given site, higher than receiving body of water e.g. adjacent Wetland pool or stream Channel.

[0046] Riffle weir grade control structures—a grade control structure comprised of boulders and gravel that concentrates low water flow in a stream or water coarse and spreads stormwater out to sheet flow, raise stream inverts to allow stormwater access to flood plains or impound shallow water.

[0047] Created aquacludes—Clay lens or other impervious layer installed below porous soil (sand or gravel bed) to direct water through porous soils.

[0048] Shallow aquatic beds—pools created with the placement of a riffle weir grade control structure in a water course.

[0049] Peatland vegetation—The systems can be designed to support peat forming vegetation and accumulate peat. Appropriate native plant species such as Atlantic White Cedar, sphagnum, nymphaea and cranberry can be planted in appropriate zones of project sites designed with these methods to accrete peat. This can result in carbon storage, improved water quality, endangered species recovery sites.

[0050] In accordance with a first exemplary embodiment of the present invention, an RSC system is provided that consists of weirs and pools. The pools are sized to provide storage of some portion or all of the WQV, Rev and for the CPV. According to a further aspect of this embodiment, if the pools provided cannot easily provide full control they can be used in conjunction with other BMPs. It is important to remember and acknowledge that each site has unique and defining features that require site-specific design and analysis. The guidance provided below is intended to assist in the design process but is not a “cookie cutter” approach. Those seeking to design and produce a system in accordance with the present invention need to be familiar with the hydrologic and hydraulic principles that are the foundation of the design.

[0051] For example, the design of a system according to the present embodiment is based on safe conveyance of the 100 year runoff. Water quality, recharge, and channel protection treatment and storage volumes are accommodated within this 100 year return frequency design framework.

[0052] A method for designing a RSC system in accordance with the present embodiment will now be discussed in reference to FIG. 1.

[0053] 1. Determine the volume of water for storage using the methods for WQv, Rev and/or CPV. Those having skill in the art understand how to calculate this value.

[0054] 2. Map out the reach where the RSC will be placed in the landscape following a curvilinear flow path whenever possible that generally follows the shape of a ravine or localized drainage path.

[0055] 3. Measure the length of the reach from its input to the discharge location.

[0056] 4. Measure the elevation difference between the top of the project reach and the bottom of the project reach.

[0057] 5. The elevation difference of the project, in feet, is equal to the target number of riffle weir grade control structures in the project. In general, each of the riffle weir grade control structures should be designed to drop one foot along its length. The construction of a riffle weir grade control structure is described in more detail below.

[0058] 6. Use the RSC formula below to determine the length of the riffle weir grade control structures and pools.

((Length of reach)/(Elevation difference))/2=Length of weir=Length of pool

[0059] If the result of the RSC formula is less than 10, the site may require one or more cascades to traverse the grade.

Length of weir=dimension of weir in direction of flow

[0060] 7. Calculate the 100-year discharge from the outlet of the project area or catchment design point.

[0061] 8. Calculate the riffle weir grade control structure width, depth, and the appropriate particle size for the weirs with a parabolic equation. Determine the width and depth of the weirs using the following: [0062] a. Design the weir to carry the 100 year storm flow in a parabolic shape. [0063] b. The minimum freeboard for lined waterways or outlets shall be 0.25 ft above design high water in areas where erosion-resistant vegetation cannot be grown and maintained. No freeboard is required if vegetation can be grown and maintained. [0064] c. Use a minimum 14 foot weir width. The width is the dimension of the weir perpendicular to the flow. Top width over constructed depth shall be greater than or equal to 10. The constructed depth is the dimension from the bottom of the weir to the top of the rock lining. (See FIG. 2A). [0065] d. Design using a cobble with a d50 of 6 inches if this is the local native stone available. The depth of the cobble is equal to:

1.5×1.5×d50 [0066] e. Use a “Manning's” roughness coefficient, n, based on the depth of water associated with the 100-year proposed conditions discharge and the cobble size:

n=d.sup.1/6(21.6 log(d/d50)+14),  (Eq. 1) [0067] Where: d=depth, ft. [0068] d50=cobble size, ft. [0069] f. Calculate the flow, Q, and velocity using a trial weir width, cobble depth, and cobble d50 size.

Q=(1.49111)(A)(Rh).sup.2/3(S).sup.1/2  (Eq 2) [0070] Where: Q=flow (cfs) [0071] 1.49=conversion factor [0072] n=Manning's n, determined by Eq 1 [0073] A=Area, which for a parabola=⅔(T)(y), [0074] where: T is top width (ft) and y is depth (ft) [0075] Rh=hydraulic radius (ft), which for a

parabola=[2(T).sup.2(y)]/[3(T).sup.2+8(y).sup.2] [0076] S=slope (ft/ft)

[0077] According to this embodiment, the flow meets or exceeds the 100 year flow and the velocity is below the maximum allowable velocity. For example, maximum allowable velocities are shown in Table 1 below, the values of which are derived from the Ishbash curve in accordance with methods known to those of skill in the art. This will be an iterative design process.

TABLE-US-00001 TABLE 1 Cobble d50 size [inches] Allowable Velocity [ft/sec] 4 5.8 5 6.4 6 6.9 7 7.4 8 7.9 9 8.4 10 8.8 11 9.2 12 9.6 15 10.4

[0078] 9. Each pool has a fixed depth of 3 feet.

[0079] 10. Design the excavation for the sand bed with a minimum depth of 3 feet and a minimum width of 4 feet along the flow path of the RSC system.

[0080] 11. The outlet pool is designed to be placed at the lowest point in the project reach. This is often in the receiving wetland or floodplain, but can also be located in upland settings where the RSC system discharges to another stormwater BMP.

[0081] 12. Next, the first riffle weir grade control structure is placed, with its bottom invert equal to the water surface elevation of the outlet pool. This weir will rise 1 foot over its length, and its top invert will be 1 foot above the invert of the outlet pool, and will set the water surface elevation of the next upstream pool.

[0082] 13. Place a footer boulder at the outlet pool elevation and in front of the weir. Then, place boulders at the weir elevation upstream of footer boulder and flanking it.

[0083] 14. At the bottom invert of each riffle weir grade control structure, design a cobble apron approximately 5 feet wide and 3 feet long that will provide a smooth transition for the flow of water from the lip of the boulder to the bottom of the downstream pool to safely convey the first flush of water when pools are dry.

[0084] 15. Place the second pool above the first weir, and continue the process of alternating pools and weirs up through the system to the entry pool.

[0085] 16. If the RSC is below a pipe system, the top invert of the weir associated with the entry pool is set to backwater the invert of the discharge pipe or culvert.

[0086] 17. Stabilize the site with woodchips or compost and seed as each section is installed. Place coarse, woody debris in pools as each section is completed. Place stabilization, seeding and top dressing notes on the plans and require labor to be on-site for the duration of the project installation.

[0087] 18. Draft a planting plan (FIG. 4), with attention to placing native plant materials in appropriate wetness zones throughout the site.

[0088] 19. Determine storage provided in pool structures by developing stage storage relationships from the grading plan. As an initial design estimate, storage volume can be determined by multiplying the surface area (determined through planimeter or computer measurement) by maximum pool depth of 3 feet and then by a scaling factor of 0.4. Compare this storage versus WQv to determine if adequate. The storage volume, V, in cubic feet, is calculated as follows:

V=(SA)(max d)(0.4) [0089] Where: SA=surface area (square feet) [0090] max d=maximum depth (ft)—recommended pool [0091] depth for RSC system is 3′ (ft.). [0092] 0.4=scaling factor to account for prismoid volume of storage pool.

[0093] 20. Determine storage volume in sand bed, Vsb, under RSC and compare to Rev. sand bed storage can be estimated as length of seam multiplied by a width of 8 feet multiplied by a depth of 3 feet multiplied by a porosity of 0.4. Compare this storage versus Rev to determine if adequate.

Vsb=(L)(w)(d)(0.4) [0094] Where: Vsb=sand bed storage volume (cubic feet) [0095] L=Length of sand bed (feet) [0096] w=width of sand bed (feet)—recommended design width is 8 feet. [0097] d=depth of sand bed (feet)—recommended design depth is 3 feet. [0098] 0.4=porosity of sand

[0099] 21. If WQv and Rev are not met by RSC design, then additional design measures must be taken to provide remaining water quality and recharge volumes.

[0100] 22. Check for Cpv control by comparing total RSC storage in pools and sand bed to total WQv and Cpv requirements. Where total RSC storage exceeds the combined WQv and Cpv requirements these criteria are fully met by the RSC system. Where full storage is not achieved, compute the peak discharge associated with the Cpv criteria and analyze discharge and associated velocities at downstream RSC weir structure using parabolic weir formula. Where velocities are shown to be 3 feet per second or less, no additional Cpv control is required. Where velocities are greater than 3 feet per second, additional Cpv storage is required at other locations in the catchment.

[0101] A regenerative stormwater conveyance system (RSC) and its constituent components in accordance with an exemplary embodiment will now be described referring to FIGS. 2-10. In FIGS. 2-10 the same reference numbers are used to refer to similar structure(s), as described.

[0102] Referring to FIGS. 2A and 2B, a complete RSC system 100 in accordance with an exemplary embodiment of the present invention is shown. In particular, stormwater enters entry pool 10 via a pipe (not shown) or some other structure, such as a culvert. As water overflows the entry pool 10, it enters a series of riffle weir grade control structures 20 and collects in an outlet pool 30. The number of riffle weir grade control structures 20 and the structure thereof is determined using the method described above in reference to FIG. 1.

[0103] As shown, for example in FIG. 4, a riffle weir grade control structure in accordance with this embodiment includes a shallow pool 400, a cobble section 410 and a boulder section 420. Each shallow pool 400 is approximately 3 feet deep at its deepest point and gets gradually more shallow as it nears the cobble section of the next downstream riffle weir grade control structure. Further, each pool 400 collects and temporarily stores water at its respective grade, or elevation, as overflowing water from the entry pool cascades through the series of riffle weir grade control structures 20. As water sits in each pool 400, it gradually filters through a compost bed 430 into a sand base 440.

[0104] Each pool 400 is separated by the cobble and boulder sections, 410 and 420, respectively, of the adjacent riffle weir grade control structure. As shown in FIG. 4, as water overflows the top of each pool 400, it travels over the upper portion of compost bed 430 which is supported beneath by cobble section 410, comprised of, for example, silica cobble. Supporting the cobble section 430 in the downstream direction is its respective boulder section 420, which keeps the silica cobble from eroding or otherwise shifting downstream under the pressure of the overflowing water from pool 400. Boulder section 420 comprises, for example, one or more 500-6000 pound sandstone boulders. Optional geotextile material 425 is placed under boulder section 420 to allow water to filter into the sand base 440 beneath boulder section 420 while preventing the soil from moving and, thus, potentially permitting the boulder(s) to shift.

[0105] Water traveling over cobble section 410 cascades over boulder section 420 and into the next downstream pool 400. In part to hold boulder section 420 in place against downstream forces, a cobble apron 450 is placed on the downstream side of boulder section 420. Water seeping through sand base 440 from upstream pools 400 exfiltrates through cobble apron 450 and enters the downstream pool. As shown, each riffle weir grade control structure enables water to gradually traverse a downward grade while filtering the water collected in each pool 400.

[0106] FIG. 5A is a cross section elevation front view of an exemplary embodiment of a riffle weir used in a regenerative stormwater conveyance system in accordance with the present invention.

[0107] FIG. 5B is a cross section elevation back view of an exemplary embodiment of a riffle weir used in a regenerative stormwater conveyance system in accordance with the present invention.

[0108] FIG. 6A is a cross section view of the boulder section 420 of the present exemplary embodiment and FIG. 6B is a cross section view of the cobble section 410 of the present exemplary embodiment. The geotextile material used in accordance with the present embodiment is ASTM D-4833 or ASTM D-463. The geotextile material is placed over the prepared surface of the excavation/fill and is anchored in place using appropriate pins or other appropriate means. Where fabric overlaps are necessary, the minimum overlap should be at least approximately 12 inches. However, a bit more or less overlap is adequate. According to this embodiment it is not necessary to put geotextile material under the cobble section 410, but this is desirable where possible.

[0109] FIG. 7 is a close-up top view of the present exemplary embodiment of a riffle weir grade control structure. In accordance with this embodiment, the boulders used to construct boulder section 420 include a footer boulder 421 positioned at the base of the boulder section 420. Each boulder is an individual sandstone boulder having a length of between 2 and 6 feet. Further, according to this embodiment, not more than 10 percent of the total weight of boulders is smaller than 15 inches in diameter.

[0110] With respect to the cobble section 410, the cobble is composed of a well-graded mixture of stone size so that 50 percent of the pieces, by weight, is larger than the d50 size determined, for example in accordance with the method described above in reference to FIG. 1. A well-graded mixture is defined for purposes of this description as a mixture composed primarily of larger stone sizes but with a sufficient mixture of other sized stones to fill the small voids between the larger stones. The diameter of the largest stone size in such a mixture is approximately 1.5 times the d50 size, for example, 8-inches×1.5=12-inches.

[0111] FIG. 8 is a cross section side view of a shallow pool 400 in accordance with the present embodiment. As shown, inverted root wad 800 is placed at the approximate center of the pool. Inverted root wads consist of a root fan and trunk of a tree with a trunk diameter at breast height of 8 to 24 inches. Root fans according to this embodiment are oblong to circular in shape and have a minimum area of 16 square feet. The attached trunk is a minimum of 5 feet in length. To place the root wad in its desired position, the trunk is sharpened, in similar fashion to sharpening a pencil, and driven into the soil at the desired position with the root mass facing upward in the shallow pool 400.

[0112] Compost 850 shown in FIG. 8 has a pH between 5.0 and 7.0 and is stable, e.g., does not reheat upon stacking. Further, the compost has a moisture content of between 30 and 55 percent and a particle size of 0.5-inches or less. For example, compost 450 is either tree leaf compost or non-tree leaf compost, such as lawn clippings.

[0113] A system according to the present invention restores ecological diversity in a manner not recognized by conventional methods. These techniques consistently result in far better stormwater treatment and wetland creation and stormwater management than do conventional approaches. A system in accordance with the invention, further, represents a unique opportunity to engage the community and to involve it in helping to restore threatened plant species to the human-shaped landscape. Finally, economic analyses of these methods have shown that they consistently return several times more value to the entities implementing them than they cost to design and build. The value of the stormwater management and wetland creation, stream restoration, and water storage has generally ranged from 3 to 8 times greater than the cost to get the project in the ground.

[0114] As has been mentioned throughout, the present stormwater management invention can be used in combination with other stream and wetland restoration applications, such as the one described in copending application Ser. No. 11/482,891, titled Sand Seepage Stream and Wetland Restoration System and Method for Ecological Restoration.

[0115] The inventive system can also replace conventional stormwater outfalls from culverts or pipes. It can be used in “rain garden” type applications alongside buildings or in highway medians to safely convey, detain, and infiltrate stormwater runoff from impervious surfaces. Systems according to the invention represent an ideal opportunity to move away from conventional stormwater holding ponds and towards sites that provide extensive stormwater attenuation, community benefit, and vital habitat. In instances where man-made structures (e.g. dams) or natural processes have caused blockages to fish migration, these systems can be used to restore fish passage and restore habitat. Finally, each of these instances where these methods are applied represents an ideal opportunity to participate in the restoration of rare, threatened, and endangered plant species populations that are often found in these peatland habitats.

[0116] The exemplary and alternative embodiments and their constituent components described above may be combined and/or modified in a variety of ways and remain consistent with the intended functionality of the invention. Furthermore, the steps and number of the various steps illustrated in the figures, specifically FIG. 1, may be adjusted from that shown without straying from the spirit of the invention.

[0117] It should be noted that the present invention may, however, be embodied in many different forms and should not be construed as limited to the embodiments set forth herein; rather, the embodiments set forth herein are provided so that the disclosure will be thorough and complete, and will fully convey the scope of the invention to those skilled in the art. The accompanying drawings illustrate exemplary embodiments of the invention.

[0118] Although the present invention has been described in terms of particular exemplary and alternative embodiments, it is not limited to those embodiments. Alternative embodiments, examples, and modifications which would still be encompassed by the invention may be made by those skilled in the art, particularly in light of the foregoing teachings.

[0119] Those skilled in the art will appreciate that various adaptations and modifications of the exemplary and alternative embodiments described above can be configured without departing from the scope and spirit of the invention. Therefore, it is to be understood that, within the scope of the appended claims, the invention may be practiced other than as specifically described herein.