Low Cost Low Impact Storm Water Designs

8/9/2019 Low Cost Low Impact Storm Water Designs

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REDUCING STORMWATERREDUCING STORMWATER

COSTSCOSTSWITH LOW IMPACTWITH LOW IMPACT

DESIGNSDESIGNS

John Walton


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Reducing Stormwater CostsReducing Stormwater Costswith Low Impact Strategieswith Low Impact Strategies

Current stormwater engineering practices inEl Paso are based primarily on dateddesigns from different climates andlandscapes

Modern low impact designs focus ondistributed points of infiltration andtranspiration for reducing peak discharge

Site specific designs that reflect the uniquegeography and climate of the El Paso del

Norte Region are needed Modern designs can lower costs and increase

profits for developers while preserving theenvironment and providing an improvedliving experience


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Low Impact DesignLow Impact DesignConceptsConcepts

Small scale controls mimic naturalhydrologic processes

Directing runoff to natural areas

encourages growth of trees andenhances infiltration

Conservation preserves natural drainagepatterns

Customized site design protects theentire watershed


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contcont

Capturing runoff in small volumes helps toprevent erosion, because the runoff is less

likely to reach damaging flow rates. The distribution of storage components also

tends to result in a more robuststormwater management system, because

the failure of one component will notcause the entire system to fail.

A knowledge based approach that requiresfull analysis of precipitation history

(drought is important for vegetation,storms for floodin )


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ExamplesExamples

Bioretention: Vegetated depressions store water insoil and provide reliable water for droughtresistant vegetation

Tree box filters: curbside containers placed belowgrade, covered with a grate and filled with sand

and soil, with tree planted in middle Infiltration trenches: fill areas with sorted gravel or

rock to capture and infiltrate runoff Permeable pavement: Asphalt or concrete that allows

infiltration

Permeable pavers: manufactured paving stonescontaining spaces where water can penetrate Disconnect impervious areas by directing runoff from

buildings and pavements onto lawns or othervegetated areas

Use weirs and check dams in swales


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El Paso SpecificsEl Paso Specifics

Arroyos move water and sediment Peak discharge causes flooding, not total

water Peak shaving/averaging will reduce flooding,

big ponds are not needed but rather smallponds that drain rapidly along withdistributed retention

Blockage of arroyos by retention pondsinterrupts sediment flow, leading to

erosion downstream Retention ponds as specified by the city

constitute a waste of resources Rainwater capture and proper peak shaving

means that detention ponds (if stillneeded) can be smaller, thereby wasting


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El Paso flooding: Rio Grande responds on time periods of days Arroyos respond in 10s of minutes

Arroyo flooding can be controlled by peaksmoothing (e.g., spread 30 minutes ofpeak rainfall over 6 hours)

Consider flow path of all water on roads andbuildings; strategically divert this flow to

retention areas (Capture area/ plant area) > 15 supports

vegetation with no watering in El Pasoclimate


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Peak ShavingPeak Shaving

Flash flood is spread over time

Leading to smoother hydrograph below

Natural hydrographs can be approximated

time

di

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ar

ge


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Example: bioretentionExample: bioretention


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Capture ZoneCapture Zone

native

plants

Impermeable areas concentrate water in vegetated areasConsider that if rainfall is increased by 10X, El Paso has a lotof water for watering trees.

capture area

capture area/plant area > 15 for El Paso


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El Paso Specific DesignsEl Paso Specific Designs


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Example: porous pavementExample: porous pavementwith groundwater rechargewith groundwater recharge


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Sediment TransportSediment Transport

Sediment transport and erosion are related Water has a sediment carrying capacity that depends

upon velocity

When the capacity to carry sediment is reached,erosion stops When sediments are artificially removed from water

by ponding, downstream erosion is increased


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Resler Canyon ExampleResler Canyon Example

Peak discharge increased by upsteam development Water comes in deficient in sediment Increased erosion visible ~1/2 mile below major

water inputs to canyon


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Resler CanyonResler Canyon


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New developments in El PasoNew developments in El Pasowouldwould

Use less city water since landscaping would bewatered by rain

Have more vegetation

Increase groundwater recharge Not increase downstream runoff or erosion Be more profitable


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ReferencesReferences

http://www.epa.gov/owow/nps/lid/costs07/ www.epa.gov/npdes/greeninfrastructure www.epa.gov/nps/lid

UFC 3-210-10 Unified Facilities Criteria (UFC)Low Impact Development Manual

(note: some bullets and images were cut and pasteddirectly from these sources)
http://www.epa.gov/owow/nps/lid/costs07/http://www.epa.gov/npdes/greeninfrastructurehttp://www.epa.gov/nps/lidhttp://www.epa.gov/nps/lidhttp://www.epa.gov/npdes/greeninfrastructurehttp://www.epa.gov/owow/nps/lid/costs07/


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Low Cost Low Impact Storm Water Designs

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