Urban Stormwater

1. Urban Stormwater John Braden University of Illinois, USA Visiting, Katholieke Universiteit Leuven Lecture 4 Leuven, Belgium March 2004

2. Outline • Stormwater management benefits typology • Benefits transfer • Case Study: Blackberry Cr, Kane Co, IL

3. Helpful Resources • Braden, J. And D. Johnston. 2004. The Downstream Economic Benefits from Stormwater Management. University of Illinois. • Johnston, D., J. Braden, and T. Price. 2004. Downstream Economic Benefits from Conservation Design Practices. University of Illinois.

4. Overview • Stormwater problems increasing w/ urban expansion • Flooding • Nonpoint pollution • Combined sewers – water quality • New approaches to site design • Benefits less quantified than costs

5. Research Questions • How do conservation design practices affect downstream resident’s benefits? • How much can conservation design practices affect downstream benefits?

6. Benefits Typology a) Reduced Flood Damages (frequency/scale) b) Smaller Drainage Infrastructure c) Reduced Pollution Treatment (low flow, storm flow) d) Reduced Erosion/Sediment Transport e) Improved Water Quality f) Improved In-stream Biota g) Improved Aesthetics h) Increased Infiltration/Groundwater Recharge

7. Valuation Issues • Marginal vs. total value • Flooding not eliminated, only reduced • Raw water unpriced at margin (in small amounts) • Transferability among studies • Location • Time • scale

8. a) Flood Reduction

9. b) Drainage Infrastructure

10. c) Reduced Pollution Treatment

11. d) Reduced Sedimentation

12. e) Improved Water Quality

13. f&g) Improved Biota and Aesthetics

14. h) Ground Water Recharge

15. Case Study: Blackberry Creek Watershed

16. Blackberry Creek Watershed Chicago

17. Case Study Methodology • Hydrologic simulation • Simulate discharge (flow rates) based on future conditions (conventional vs. conservation) -- HSPF • Calculate the flood heights (HEC-RAS). • Estimate flooded areas (High-Res. DEM) • Flood benefits • Estimate the area of different land uses contained within the flooded area • Assess the differences in flooded area between scenarios and calculate the economic benefits for the unflooded area • Infrastructure benefits – size and cost differentials for peak flows

18. Conservation Design Objectives Images courtesy Conservation Design Forum, Inc

19. Flow Simulation

20. Floodplain Delineation

21. Conservation Scenario

22. Land Use within Floodplain

23. Land Use

24. Benefit Area

25. Flood Damage Estimation

26. Infrastructure Estimation • Represented by culvert sizing to accommodate design flows at all road crossings • Lesser peak flows smaller culverts, reduced costs

27. Infrastructure Cost Differential

28. Hydrology Results • Average of a 40% reduction in peak flows in the conservation design scenario • Water surface elevation (flood stage) differences between the two scenarios range from 0 ft in headwater areas to 1.5 feet at the mouth of the watershed • Velocities in the streams are also lower in the conservation scenario

29. Economic Results • Flood Reduction Benefits • $14,500 to $36,300 per acre (assessed value) • $7,800 to $19,600 per acre (median housing value) • $0 to 7,800 (properties at reduced risk) • $54-$343 per developed acre • Infrastructure Benefits • Substantial cost savings in avoided costs of capacity expansion downstream of conservation practices • $247 to $338 per developed acre for existing structures • Avoided channel rehabilitation/erosion prevention

30. Conclusions • Assessment limited by models, data, and resource constraints. • Assumes general implementation of conservation design strategies over projected developed areas. • Substantial downstream savings – savings to public and environment.