1. Update to the 1992 Dry Creek Watershed Flood Control Plan CESI/RBF RR/KM FEMA CTP HYDROLOGY

2. Purpose of the Plan Update To develop updated hydrologic model that can adequately evaluate the flood damage reduction potential of achievable projects, Asses the impact of the development that has occurred with realistic consideration of the effectiveness of local developer installed detention basins, Identify plausible multiple objective regional flood reduction and/or mitigation measures that could be expected to be met with broad support, Provide a list of local, cost effective, flood damage reduction projects, and Prepare a funding plan consistent with Plan Update project recommendations and current development projections Update to the 1992 Dry Creek Watershed Flood Control Plan

3. New Modeling Major Revisions to the Previous (1992) Plan Model –Watershed Boundary Changes Finding Mitigation in the Urbanized Dry Creek Watershed

4. New Modeling Major Revisions to the Previous (1992) Plan Model Watershed Detail Substantially Increased. 170 watersheds became 1,250+ watersheds. Finding Mitigation in the Urbanized Dry Creek Watershed

5. New Modeling Major Revisions to the Previous (1992) Plan Model –HEC-HMS replaces HEC-1 for individual hydrograph development portion of modeling. Integrated GIS functionality Adds greater Flexibility in Future –DRY CREEK TOOLBOX Update to the 1992 Dry Creek Watershed Flood Control Plan

6. Baseline Comparison 1992 Estimated Imperviousness of the Watershed = 17.8%. Dry Creek Watershed Imperviousness 1992 Finding Mitigation in the Urbanized Dry Creek Watershed

7. Baseline Comparison Current Estimated Imperviousness of the Watershed = 22.0%. Dry Creek Watershed Imperviousness Current Finding Mitigation in the Urbanized Dry Creek Watershed

8. Baseline Comparison Future General Plan Build-out Estimated Imperviousness = 27.0%. Dry Creek Watershed Imperviousness Future GP Build-out Finding Mitigation in the Urbanized Dry Creek Watershed

9. Baseline Comparison The development area of the watershed has increased from 35,900 acres to 44,400 acres, and will increase to 58,700 acres at General Plan build-out. Timeline ConditionAcreage of Development (acres) Rural Residential Portion (acres) 199235,9009,000 Current44,40012,300 General Plan Build-out 58,70017,200 Finding Mitigation in the Urbanized Dry Creek Watershed

10. Historical Flooding in the Watershed Documented Recent Major Floods: Feb 1986 (50-100 yr) Jan 1995 (200-yr) Dec 1995 (2-yr) Jan 1997 (10-yr) Feb 1998 (10-yr) Dec. 2005 (10-yr) Finding Mitigation in the Urbanized Dry Creek Watershed

11. Historical Flooding in the Watershed JAN 1995 –2-day event – 358 Structures Flooded within Roseville. –Rainfall Matched 200-year intensities for a 6-hour and 24-hour storm event. –Between 3.9 inches and 7.6 inches of rain in Dry Creek Watershed –End of strong (5-year) El Nino/beginning of weak La Nina event Finding Mitigation in the Urbanized Dry Creek Watershed

12. Historical Flooding in the Watershed What to Avoid! Update to the 1992 Dry Creek Watershed Flood Control Plan

13. Historical Flooding in the Watershed Comparison of Pacific Pressure (El Nino effect) Update to the 1992 Dry Creek Watershed Flood Control Plan 1986JAN 1997 JAN 1995 DEC 2005 DEC 1995 JAN 2010

14. New Modeling Major Revisions to the Previous (1992) Plan Model –Hydraulic Routing Model as a Hydrologic Component (HEC- RAS) Update to the 1992 Dry Creek Watershed Flood Control Plan

15. Dry Creek Watershed Study Update Calibration

17. Dry Creek Watershed Study Update Technical Analysis Status Raw Precipitation Values published in SWMM

18. Dry Creek Watershed Study Update Technical Analysis Status Raw Precipitation Values published in SWMM

19. Dry Creek Watershed Study Update Calibration

28. New Modeling Major Revisions to the Previous (1992) Plan Model –Storm Centering: Analysis of all 1200+ storm centers and 4 different potential storm angles at each storm centering location, yielded 7 storm combinations that can control peak flows for the various locations in the watershed. DRY CREEK TOOLBOX

29. Dry Creek Watershed Study Update Technical Analysis Status Raw Precipitation Values published in SWMM

30. Dry Creek Watershed Study Update Technical Analysis Status Raw Precipitation Values published in SWMM