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Addressing Hydrology at the Watershed Scale: A Novel Approach to Stormwater Management with a Water Supply Nexus - Chris Herrington
1. The document discusses how humans have altered urban hydrology through increased impervious cover and proposes distributed small-scale stormwater controls as a solution. 2. Modeling showed that distributed controls like rain cisterns and rain gardens, even at low adoption rates, could meaningfully improve hydrologic metrics and provide water supply benefits by reducing runoff. 3. Implementing distributed stormwater controls across different land uses has the potential to shift urban hydrology in a way that approximates reducing effective impervious cover by 25%.
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Addressing Hydrology at the Watershed Scale: A Novel Approach to Stormwater Management with a Water Supply Nexus - Chris Herrington
- 1. 1 Christopher Herrington, P.E. 512-974-2840 Chris.Herrington@AustinTexas.gov AddressingHydrology at the Watershed Scale A Novel Approach to Stormwater Management with a Water Supply Nexus
- 2. 1. Humans alterhydrology, and hydrology is king 2. Storage is the solution to altered hydrology 3. Distributed small-scale stormwater controls can be a meaningful solution to altered hydrology (with benefits) 2 Executive Summary Urban Hydrology Restoration, Proof of Concept Modeling report austintexas.gov/watershed_protection/publications/document.cfm?id=268805
- 3. More people means… 3 •More wastewater to manage • Land becomes more expensive • Increased demand for potable water • More impervious cover = degraded stream function
- 4. Humans change Hydrology 4 “TheUrban Stream Syndrome” – Walsh et al. 2005
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- 6. 6austintexas.gov/watershed_protection/publications/document.cfm?id=196394 % Impervious Cover Fraction of Rainfall that becomes runoff #Runoff Events per Year Annual Runoff (inch) 0 0.064 46.0 1.18 100 0.781 73.4 22.91
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- 9. The (hydrology) Problem Anthropogenicdisturbance (eg, impervious cover): • reduces rainfall infiltration • decreases creek baseflow • increases stormwater runoff, flooding • increases erosion, pollutant loading
- 10. Stream Function Pyramid 10Harmanet al. 2012
- 11. How do wefix hydrology*? STORAGE 11 *in a cost-effective way
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- 13. When it stopsraining… 13 24% 9,429,728,998 gal/year
- 14. Annual average waterdemand-Austin Citywide • Outdoor uses = 24% of total citywide demand Residential indoor non-potable uses (toilets, clothes washers) • Single-family = 27% of total sector demand • Multi-family = 32% of total sector demand 1441.5%
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- 16. One Water: Integrated WaterResource Management Integrated water resources management is based on the equitable and efficient management and sustainable use of water and recognizes that water is an integral part of the ecosystem, a natural resource, and a social and economic good, whose quantity and quality determine the nature of its utilization. -Global Water Partnership 16
- 17. Green Stormwater Infrastructure 17 Centralized,Regional, Community Decentralized, Building
- 18. Fixing today’s Austinflood, erosion and water quality problems Can I borrow $2,263,142,800? (let’s talk about maintenance later) (p.s., it will take 87 years just to fix today’s problems) Austin Watershed Protection Master Plan
- 19. Centralized, Regional GSI Significanteconomy of scale, but: • Opportunities for construction are limited – Land increasingly expensive • Each project increases maintenance burden • Construction and O&M paid entirely by utility • Failures are “big” • Does not offset demands on potable water 19
- 20. Decentralized, small-scale GSI •Constructed on private land – High degree of opportunity in urban watersheds • Reduced burden on utility • Failure impacts smaller and distributed • Can offset demands on potable water But, is there any hydrologic benefit? 20
- 21. Proof of ConceptModeling Can distributed, small-scale stormwater controls provide a meaningful intervention in urban hydrology?
- 22. Proof of ConceptModeling Existing Regional Controls Distributed + Regional Controls
- 23. Distributed Control Scenarios 23 LandUse Category Total Paved IC Total Roof IC IC area treated Total # ParcelsMax High Low Single Family 18.1 61.1 79.2 45.8 15.3 1,257 Multifamily 8.0 6.9 14.8 9.1 3.1 40 Commercial 37.3 25.6 62.9 37.9 12.7 88 Office 9.2 5.7 14.9 8.9 3.0 22 Industrial 18.6 15.9 34.5 21.2 7.1 40 Civic 32.8 11.6 44.4 25.1 8.5 13 % of IC treated 71.4 % 42.2 % 14.2 % % of surface area treated 26.4% 16.0% 3.4%
- 24. WLR3: Rain CisternSizes 24 Land Use Category Average roof area (acres) Cistern volume (gallons) Single Family and Duplex 2,150 2,500 Multifamily 6,933 8,000 Commercial 10,522 12,500 Office 10,427 12,500 Industrial 16,688 20,000 Civic 13,605 15,500 All roof surfaces treated, capturing up to 2 inch rainfall
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- 26. SWAT Model 26 Topography +Soils + Land Use = Hydrology
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- 29. Ratio of Baseflowto Total Flow
- 30. Ecologically Significant? At lowrain cistern saturation, change in hydrologic metrics correspond to 20% improvement in Austin aquatic life multi- metric index scores 30
- 31. Water Supply Benefits? •27% reduction in “water stress days” • 11% increase in evapotranspiration • Potential to offset demand on potable supply 31
- 32. Lessons Learned • Hydrologyshifts proportional to density of treatments • Hydrologic improvement even without treating transportation land use • Equivalent to a potential reduction in of 25% effective impervious cover 32
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- 35. 1. Humans alterhydrology, and hydrology is king 2. Storage is the solution to altered hydrology 3. Distributed small-scale stormwater controls can be a meaningful solution to altered hydrology (with benefits) 35 Executive Summary Urban Hydrology Restoration, Proof of Concept Modeling report austintexas.gov/watershed_protection/publications/document.cfm?id=268805
- 36. Texas Water ResearchNetwork esi.utexas.edu/research/texas-water-research-network/ Save the Date! January 11-12, 2018 Austin, Texas
Editor's Notes
- #4 Austin MSA 3rd fastest growing in the US. Hays County fastest growing county in Texas and 5th fastest growing in the nation From 1997 to 2012, Texas was adding about 500,000 people per year with 65% of the increase in top 10 most populated counties and about 12% of that growth in the Texas Hill Country
- #13 Current stormwater management paradigm in urban areas can cause flooding and erosion impacts downstream, carries pollutants into our Hill Country creeks and aquifers
- #15 >41.5% of uses can be satisfied with non-potable water
- #19 Government cannot solve this problem alone on a human time scale 87 years = 2104…that’s the difference between today and 1930.
- #24 Transportation land use impervious cover not treated by this approach