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Babcock Basin-Design Phase
Ellen Stevens, Ph.D., P.E., PLLC in collaboration with G A GOSE & ASSOCIATES
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Project requirements and methods for incorporating public values and interest
Focus on a Regional stormwater management solution Don’t just move the problem downstream Use LID where feasible – solve the problem at the source Consider acquisition where politically feasible No Adverse Impact – NAI Model both LID and conventional stormwater facilities Produce a valid pre- and post-project comparison
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Assessment of the identified problem areas and propose conceptual solutions
Solutions were developed to satisfy the following objectives: Provide safe conveyance to protect homes from flooding and keep roadways safe for travel Infiltrate or otherwise slow down runoff upstream to reduce the amount of hard infrastructure required downstream Be implemented with No Adverse Impact Ideally, two or more alternatives can be developed for each identified area, to allow for selection based on cost, effectiveness in mitigating the problem, and environmental benefits or preserving and restoring the natural and beneficial functions of creeks and riparian areas
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Culvert on W. Summerlin Court
Grass swale to further slow down runoff Potential to detain 25 acres upstream Culvert on W. Summerlin Court
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Conventional Solution
Problem: Culvert is undersized and will overtop in relatively frequent events. Overtopping discharge flows east on roadway and flows to intersection of W 23rd and Summerlin Ct. LID Solution Convert existing farm pond to wet detention (25 acre DA) Grass swale through low area upstream of culvert Reduce discharge and sediment load into culvert, then re-evaluate culvert capacity Conventional Solution 5-foot deep vertical wall concrete channel Replace culvert with double 6’ x 4’ RCB Convey stormwater rapidly to outlet south of church
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Inadequate Easements - Lots 23 and 24 in Summerlin Addition
Buy lot and install bioretention Install enhanced bioswale to slow down runoff Approximately 13 acres drains to lot Inadequate Easements - Lots 23 and 24 in Summerlin Addition
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Conventional Solution
Problem: Runoff from approx. 13 acres is collected in an easement between lots 23 and 24. Easement is inadequate and situation will be worse if a home is built on the lot LID Solution Grass swale or enhanced bioswale upsream to reduce runoff Buy lot and install landscaping features that promote infiltration Reduces flow into easement and street; prevents building of a future home that is likely to be damaged Conventional Solution Construct larger concrete channel between lots; may require more easement May need storm sewer between lots and W 23rd Very disruptive to street; future home may still be susceptible to damage
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Excess Water in Intersection of Summerlin Ct. and W 23rd
Buy out one home and use lot for open channel Install grates to intercept runoff LID solutions proposed for upstream areas should help the intersection Excess Water in Intersection of Summerlin Ct. and W 23rd
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Problem: Runoff going north on Summerlin Ct
Problem: Runoff going north on Summerlin Ct. to the intersection does not turn the corner and go west to the flume at the end of the cul-de-sac LID Solution The measures proposed for the culvert and the easement should reduce the amount of runoff in the intersection – reducing the size of storm sewer required Consider buying out one home to construct open channel to south and west (not likely to be feasible, even if cost-effective) Conventional Solution Construct grates in Summerlin Ct. to intercept runoff and convey in storm sewer Some configuration of grates and a storm sewer appears to be only feasible solution
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Curb cut and very small channel between homes
Channel is small and close to house This lot now built Street will eventually be required to convey runoff from about 6 acres of dense development Curb cut and very small channel between homes
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Conventional Solution
Potential Problem: There is a curb cut with a very small channel west of last duplex. Once this street is built out, channel may be too small Recommendations Does not appear to be amenable to LID solution Analyze full development runoff and determine if homes by channel are at risk Conventional Solution Remove curb cut if street is adequate for runoff from all lots Install inlets and storm sewer between homes
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Grates in Countryside Addition
Approximately 10 acres drains down street to grates Grates in Countryside Addition
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Conventional Solution
Problem: About 10 acres drains to two grates on 22nd Ct. There is no overflow flume for any bypass from the grates, so excess runoff could enter homes Recommendations Does not appear to be amenable to LID solution Analyze full development runoff and determine if grates are undersized Verify that street can convey flow within curbs Conventional Solution Replace grates with larger grates if needed Install larger pipes if needed Install relief flumes in cul de sacs if feasible
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Compliance with all federal, state and local regulations and design criteria, as appropriate
City drainage and floodplain standards FEMA policies (although only a very small portion of the watershed is in FEMA floodplain) Corps of Engineers 404 permitting, if blue line is to be disturbed Specify contractors obtain coverage under construction general permit and develop SWPPP if sufficient area disturbed
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Compliance with all federal, state and local regulations and design criteria, as appropriate
Comply with NEPA requirements for federally-funded projects: Endangered species Prime farmland Historical and archaeological sites Measures to minimize air and noise pollution Environmental justice Most of these are clearly not a problem in this location, but still need to be documented
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THANK YOU Ellen Stevens, Ph.D., P.E., PLLC G GOSE & ASSOCIATES A
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