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Table 5: Twenty-four strategies to minimize impervious area at the site level (adapted from City of Olympia, 1994; Schueler. 1995; and PZC, 1992) _ 1. Narrower residential road widths 2. Reduced road lengths 3. Hourglass streets 4. Cluster development 5. Shared driveways 6. Angled parking with one way traffic flow 7. Smaller parking stalls 13. Vertical parking structures 14. Two and three story buildings 15. Stream buffers 16. Grass swales rather than curb/gutters 17. Open space requirements (residential) 18. Open space landscaping requirements (comm). 19. Sidewalks only on one-side of street 8. Reduced parking space ratios for some uses 20. Reduced side and rear yard setbacks 9. Shared parking facilities `~ commercial areas 21. Decrease distance between lots (frontage) 10. Shorter residential driveways 11. Reduced cul-de-sac radii 12. Cul-de-sac donuts 22. Hammerhead-shaped turnarounds 23. Rear yard grading to buffer 24. Permeable spillover parking areas Conclusion Research has revealed that imperviousness is a powerful and important indicator of future stream quality and that significant degradation occurs ar rela- tivelylow levels of development. The strong relation- ship between imperviousness and stream quality pre- sents aserious challenge for urban watershed manag- ers. It underscores the difficulty in maintaining urban stream quality in the face of development. At the same time, imperviousness represents a common currency that can be measured and managed by planners, engineers and landscape architects alike. It links activities of the individual development site with its cumulative impactat the watershed scale. With further research, impervious cover can serve as an important foundation for more effective land use plan- ning decisions. References i. Benke, A. E. Wi]leke, F. Parrish and D. Stites. 1981. Effects of urbanization on stream ecosys- tems. Completion report ProjectNo. A-055-GA. Office of Water Research and Technology. US Dept. of Interior. 2. Black and Veatch. 1994. Longwell Branch Restoration-feasibility study. Vol 1. Carrol County, MD Office of Environmental Services. 220 pp. 3. Booth, D. 1991. Urbanization and the natural drainage system-impacu, solutions and prog- noses.. Northwest Environmental Journal. 7(1): 93-1 18. 4. Booth, D. and L. Reinelt. 1993. Consequences of Urbanization on Aquatic Systems.- measured effects, degradation thresholds, and corrective strategies.pp. 545-5~0 in Proceedings Water- shed '93 A National conference on Watershed Management. March 21-24, 1993. Alexandria, Virginia. 5. City of Olympia, 1994(a). Impervious Surface Reduction Study: Technical and Policy Analy- sis-Final Report. Public Works Department, Olympia, Washington. 83 pp. 6. City of Olympia, 1994(b), Impervious Surface Reduction Study. Draft Final Report. Public Works Department. City of Olympia, Washing- ton. 183 pp. 7. Duda, A and K. Cromartie. 1982. Coastal pollu- tion from septic tank drainfields. Journal of tl~e Environmental Engineering Division (ASCE) 108 (EE6). 8. Evett et al. 1994. Effects of urbanization and land use changes on low stream flow. North Carolina Water Resources Research Institute, Report No. 284. 66 pp. 9. Galli, J. 1991. Thermal impacts associated with urbanization and stotTttwater management best management practices. Metropolitan Washing- . ton Council of Governments. Maryland Depart- ment of Environment. Washington, D.C. 188 PP• 10. Galli, J. 1993. Rapid Stream Assessment Tech- nique.Metropolitan Washington Counci 1 of Gov- eriiii%nu. `:'as hington, D.C. 110 ~~a~~?~~a~a~l,~:a~r.~~~r!?~-~~c7C^,~4'~=~ O ~,~C , `t~lh~;~' Lj ~~~(~~~1:;