Prepared by: Burnham – Floodplain Study October 23, 2009 Presented by: Marty Spongberg, PhD, PE, PG AMEC Geomatrix, Inc.

2 Burnham Parcel

3 Water Code Section (c) The board shall, in any evidentiary hearing, consider all of the following, as applicable, for the purpose of taking any action pursuant to Section 8560:. (2) The best available science that relates to the scientific issues presented by the executive officer, legal counsel, the department, or other parties that raise credible scientific issues.

4 Precedence for Modification to Floodway Maps – Kaweah River Map 1SA

5 Precedence for Modification to Floodway Maps – Kaweah River Map 3SA

6 Basis for Establishing River Stage CVFPB – Staked locations reported to be high water marks FEMA – Hydraulic modeling calibrated by reported high water marks

7 Basis for Establishing Flow Rate CVFPB  80,000 cfs  Basis – reported high water, topography  Return Interval - ? FEMA  73,000 cfs  Basis – USGS gaging station  Return Interval – 140-year

8 Comparison of Designated Floodway and FEMA FIS Maps

9 HEC-RAS Study (Flow = 73,000 cfs)

10 HEC-RAS Study (Flow = 80,000 cfs)

11 CVFPB Issues (a)The current request for modification of the floodway boundary will move the boundary within the actual river channel, thereby reducing any inherent factor of safety provided by a conservative estimate of the boundary location. (b) There is significant staff work associated with an approval of a designated floodway modification. Affected map sheets must be revised and renumbered, the revised maps sent to Tulare County recorders office as an official document, and the Board’s records and website updated.

12 CVFPB Issues (continued) ( c) Calculations by the consultant and Board staff, show that the Island Building Pad would be 0.2 feet to 1.00 feet below the 100 year storm (1% chance). In storms that exceed this frequency, the Building Pad would be inundated. This does not consider Wind Wave Run-up (1.0 feet to 2.0 feet) nor margins of error within the Hydrology calculations.

13 CVFPB Issues (continued) (d) There has been no discussion of the likelihood of large boulders which are carried through this river course which do damage and present a clear danger to life and property. The U.S. Army Corps of Engineers, Sacramento District, California, prepared a Flood Plain Information packet for the Kaweah River at Three Rivers, California on October They state that Kaweah River velocities can reach up to 20 feet per second and “…velocities would be slightly higher on all streams and would be extremely dangerous to life and property.” On page 3 of the above mentioned report, the U.S. Army Corps of Engineers states; “Hazardous Conditions would occur during large floods as a result of rapidly rising streams, high velocities and deep flows.”

14 Cross Section 8

15 CVFPB Issues (continued) (e) If a residential structure were to be allowed, it would create an in-stream blockage which would decrease flow area and increase velocities causing negative impacts both upstream and downstream.

16 Summary The current Designated Floodway Map is inaccurate, and should be modified to reflect detailed survey information and engineering studies. Safety Factor - Our request is to modify the map to reflect river stage for flows that are 10% greater than the 140- year flow.