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Hansen Mine Ditch Water Conservation ProjectBackground: The project is located in the East Branch of East Weaver Creek watershed, just upstream of the confluence of the East Branch and East Weaver Creeks. The project area was part of an 1800’s patented mining claim, referred to as the Hansen Patented Mining Claim. The patent included a water right and the patent holders divert 1 cfs of East Branch of East Weaver Creek. This water is taken from the East Branch via a side hill ditch and conveyed for ~ 0.4 miles southeast before entering a pasture. The patented mining claim was subdivided in the 1950’s conveying a portion of the water right to five parcels lying along the ditch. The landowners collectively maintain the ditch, installing the intake into East Branch Creek in May or June and pulling it out in October of each year. The end landowners report that they file a water right notice with the CA Department of Water Resources every three years. The water is used for irrigation of lawns, orchards and 3.3 acres of oat and grass fields that pasture horses. Water use consists of sprinkler irrigation for orchard trees and lawns and flood irrigation of the pasture. A dense, highly productive but narrow band of incense cedar, ponderosa pine, and Douglas-fir with riparian hardwood trees (white alder, CA black oak and apple) has grown along the ditch and is in sharp contrast to the native oak and pine woodlands of the general area. This narrow tree band averages approximately 420 ft2 basal area and more than 60,000 board feet of conifer timber on a per acre basis. This density makes this narrow band among the most highly productive forest stands in the area with board foot volumes comparable to redwood forest of similar age and site index. The preservation of this band of trees is a priority of most of the landowners. A landowner piped the southernmost end of the ditch approximately 15-20 years ago. The resulting loss of ground flow caused tree mortality of about 40%-50% with approximately 50% of the remaining trees showing reduced vigor, top dying, thinning crowns, or other stresses.Excess flow off of the pasture is captured in a road ditch and returned to an ephemeral stream that is a tributary to East Weaver Creek. Observations of the mouth of that stream in early July 2012 found only a minor trickle of surface flow rejoining East Weaver Creek. It is speculated that a downstream landowner may have a diversion in the stream. Implementation of this project would eliminate nearly all of that diversion, if one exists.Periodic in stream flow estimates were made in the ditch on July 1, 2012 as shown in the following table:Measurements Taken on July 1, 2012 between 8:30-10:30 amDaily Total GallonsDaily AC FTFlow Rate cfsEstimated Stream Flow Upstream of Diversion2,908,2248.934.50Estimated Stream Flow Downstream of Diversion2,261,9526.943.50Diversion at East Branch Ditch646,2721.981.00Return Flow From Leaks Near Mouth of Ditch239,1210.73(0.37)Ditch Flow at ~400’ from Mouth387,7631.190.60Return Flow From Leaks at ~450’ from Mouth25,8510.08(0.04)Diverted Flow at End of Ditch at ~2,000’316,0270.970.49Based on the field measurements, assumptions were developed regarding evapotranspiration rates and ditch losses, and projected consumptive uses of water. These assumptions were used to develop a water budget as shown in the following table:Measurements Taken on July 1, 2012 between 8:30-10:30 amDaily Total GallonsDaily AC FTFlow Rate cfsPeak Leakage, Evapo-Transpiration Rates Estimated/Day=Soil Recharge Volume/Day91,4110.280.14Water Users Other Than Truman10,0000.030.02Truman Water Demand40,7290.130.06Water Demand Contingency Factor18,5160.060.03Total Diversion Water Demand160,6550.490.25 The water budget is based on the following assumptions:Approximately 54% of the total ditch diversion leaks out, but most of that occurs near the stream diversion point and returns to East Branch Creek. There is a constant small leak at the ~450’ point of the ditch. Beyond that point, the ditch leakage drops to 27% of the measured flow.Evapo-transpiration rates were relatively low at the time of field measurements (research papers on transpiration rates support this conclusion). Transpiration rates were estimated at 35% of probable rates of 200 gallons/mature tree/day for 225 mature trees. Evaporation rates were estimated at 1 gallon/ft2/day (the ditch has 100% shade canopy with high relative humidity).Consumptive use at the time of inventory was low (estimated at 250 gallons per hour), with no observed irrigation occurring. Nearly all water loss in the ditch past the ~450’ point was due to natural leakage rates (including evapotranspiration rates) and is estimated at 27% of flow (studies suggest ditch loss rates are highly variable ranging from 20% for well-maintained ditches to 50%+ for poorly maintained ditches). There was no evidence of excessive leakage (channels, bogs, ponds, wetlands, etc) downslope of the ditch after the ~450’ point on the ditch. The pasture irrigation rate for oats is assumed to be ~5 ac ft. per acre per growing season. All other landowners are assumed to use up to 10,000 gallons/day for all consumptive uses.Proposed Project:This project will consist of:1600 Agreement with CA Department of Fish and GameManufacture and installation of a fish screened mechanical head works and appurtenant power if needed;Upgrade of the well intake on the Colbeck/Chilcote parcel if needed;Purchase and installation of 5,000 gallon water tanks installed for up to five parcels subject to proof of a deeded water;Modification of the tail work intake to flow ~65,200 gallons in 6 hours into the inlet into an 8 inch diameter PVC irrigation pipe. Any overflow will be directed into the existing overflow channel.Installation of ~800’ of 8” PVC buried trunk irrigation line and 1,200’ of 2” K-line, or combination K-line/solid set irrigation system, or similar sprinkler irrigation for the pasture.Installation of pumps and pressure tank as needed.The head works will be located approximately 100’ into the ditch (outside the floodplain of the East Branch) and will designed to either open from 12 am to 6:00 am each day, flowing 1cfs for 6 hours (~161,568 gallons) or will flow a lower volume continuously. A passive tail works inlet will trigger irrigation of the pasture until flows recede with the closing of the headworks. Depending on the headworks configuration a pressure tank/pump may be used to assure irrigation of the pasture area. It is anticipated that the combination of ditch leakage/soil recharge and irrigation will consume all of the flow; however, overflow will be diverted into the existing channel. If an activated headworks is installed, the timing of the diversion would coincide with the highest stream flows, so as to minimize impacts on fisheries and water quality. The headworks would open late at night when evapotranspiration rates of trees are lowest. Local streams experience significant daily fluctuations in flows in response to evapotranspiration rates with peak flows occurring in late night. In addition air and water temperatures are lowest late at night. Therefore, taking water at night will maximize daily flows in the creek to the benefit fisheries.Environmental Review:The project is Categorically Exempt under Section 15333 consisting of projects that do not exceed five acres in size to assure maintenance, restoration, enhancement, or protection of habitat for fish, plants, or wildlife provided there would be no significant adverse impact on endangered, rare, or threatened species or their habitat pursuant to Section 15065 and the other requirements set forth in of Section 15333 (b)-(d). This project will benefit fish and wildlife by retaining streamflow in East Branch of East Weaver Creek and installing a fish screen on the Hansen Mine Ditch. It will not require significant earthwork or grading. The entire disturbed areas are less than 0.1 acre. The new head gate and screens will be located approximately 100’ from the ditch and creek confluence and will disturb approximately 100ft2 of area of the ditch line. Trenching for electrical lines will disturb less than 300 ft2 of area. Modification of the tail works structure will not disturb more than 50 ft2 of the ditch area. Trenching of 800’ of irrigation line in a developed pasture will disturb ~2,400 ft2, and minor pad development for water tanks located in existing yards of homes will affect ~500 ft2.Above: Diversion inlet looking upstream (July 10, 2012)Below: Ditch segment and diversion inlet looking downstream (July 10, 2012) Above: Ditch berm with knockouts and leakage and tree growth. Below: flood irrigated pasture ................
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