Pájaro River Watershed Flood Protection Plan - The Pajaro River ...

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measurement and only 2,100 cfs higher than rating 38. It is still a peak of record as are the peaks for San Benito and Tres Pinos. Please note that there is a major tributary entering the Pajaro River upstream of the confluence of the Pajaro and San Benito rivers. Uvas Creek has a drainage area of 71.2 square miles at the old USGS gage (1959-1992) Uvas Creek near Gilroy (11154200). I don't know what the DA is at the confluence with Pajaro. We don't know what the flow contribution or timing of the peak for Uvas Creek actually is. Peaks are regulated by Uvas Reservoir. Santa Clara Valley Water District now operates this gage. I would like to take over the operation of that gage once again as the peak flows seem to be a key element for validating flows at Chittenden. Another item to note is that the peak at Chittenden occurred 45 minutes before the peak at the San Benito site. If one looks at the total runoff in acre feet for both of the sites, the numbers make sense. The total runoff at Chittenden was much higher. February ACFT for San Benito at HWY 156 was 130,500 while ACFT for Pajaro at Chittenden was 387,500. Other factors which are being overlooked or unknown are; 1) there is a huge, natural, heavily forested and overgrown floodplain area where the San Benito meets the Pajaro that acts as a reservoir to store peak flows. I don't know how much it could put into storage and then release. It's not too hard for me to imagine this possibility looking at the height of the post-flood drift in trees I could see from HWY 101. 2)there is also a large area of low lying farmland on the San Benito R above this area which was under several inches to feet of water. This storage component is very real. If one compares the hydrographs for San Benito vs Pajaro, the San Benito peak is much more flashy than the Pajaro peak. This is a common occurrence for flood peaks at these two sites. Given all of the above, including the large uncertainties in the Slope Area measurements, I see no big problem here. I have also made a suggestion to the US Army Corp of Engineers to develop a plan to map flooded areas and run calculations for storage the next time we see a major event. They too were concerned with the apparent numerical discrepancies between peak discharges at these two sites. My contact at the San Francisco office is Carlos Hernandez. Larry. Larry Freeman Field Office Chief USGS 3239 IMJIN ROAD DRAFT 7/22/03 47 Pájaro Watershed Flood Management
APPENDIX 5 Example of Historical Changes in the Lower San Benito River Fig 18-19: Top photo, December 2000; bottom photo, June 1939 See Fig 20-21for topographic maps of this site. River flow is from right to left. Overbank floodplain areas are clearly visible in 1939, as is a wide aggrading sand-filled channel. Mining beginning in the 1940’s has now lowered the channel 15-20 feet or more to intersect groundwater. An incised channel can be seen in the vegetated mined-out area today. Some areas of original flood plain in 1939 DRAFT 7/22/03 48 Pájaro Watershed Flood Management
Page 1 and 2: California State University Robert
Page 3 and 4: Table of Contents Executive Summary
Page 5 and 6: Pájaro River Watershed Flood Manag
Page 7 and 8: that today bears the name Pájaro.
Page 9 and 10: Map B. 1908 Parcel Map of a portion
Page 11 and 12: Map A 1875 based on 1854 land surve
Page 13 and 14: Upper Watershed, San Benito and San
Page 15 and 16: Himalaya and Alaska are there possi
Page 17 and 18: DRAFT 7/22/03 17 Pájaro Watershed
Page 19 and 20: The current project attempts to rec
Page 23 and 24: where: g adj is the adjusted skew g
Page 25 and 26: 70000 Hollister upper confidence in
Page 27 and 28: value for the maximum possible 100-
Page 29 and 30: Regional Analysis The trend in perc
Page 31 and 32: Interestingly, the maximum consecut
Page 35 and 36: We also find that on the order of 6
Page 37 and 38: Figure11 Cartoon showing how incisi
Page 39 and 40: Although Hospital Road shows some a
Page 41 and 42: clearly attenuate (reduce) flood pe
Page 43 and 44: average 8-foot depth of water that
Page 45 and 46: culverts and fill. Other parts of t
Page 47 and 48: Our modeling of enhanced flood stor
Page 49: APPENDICES & Figures APPENDIX 1: No
Page 53 and 54: APPENDIX 2: 1995 and 1998 Storm Com
Page 55 and 56: http://12.45.109.6/pls/portal30/get
Page 57 and 58: 50 Corralitos Creek Hydrograph & Co
Page 59 and 60: Figure 16 - San Benito River channe
Page 61 and 62: Fig 15 Stream Barb Structures DRAFT
Page 63 and 64: Corps’ Data presented Alternative
Page 67 and 68: . illustrations, on an interim repo
Page 69 and 70: APPENDIX 3 Streambank Property Owne
Page 71: Historical Change in San Benito Riv

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