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' Memorandum to Hemy Bazbe, MCC July 28, 2000 t Page 2 ' sand with a diameter of about 0.30 millimeters. The other photographs, Photo 2 through Photo 8 were taken proceeding upstream from the Lower gage towazd the Upper gage. ' All photographs with the exception of Photo 6 aze examples of the channel hydraulic characteristics, vegetative growth, old logjams, bankline slopes, bank sediments both stable and eroding, and the bed material in the channel bottom. Photo 6 shows the sand size sediments ' deposited above the approximate 8-foot high beaver dam. This lazge deposit of sand above the beaver dam along with deposits of sand material between the cobbles or boulders in the channel ' support the significant quantity of sand size sediments being transported in the channel during flood flows. There were several locations of an eroding bank such as shown on Photo 4 where finer silt size sediments would be eroded and transported downstream. In general, Deep Creek is a perennial stream that is well incised and is degrading over time. The rate of degradation is slow as evidence by the cobbles and boulders scattered over the streambed. ' The channel bottom has not become fully armored. Thus, further degradation can be expected. but with the amount of lazge rocks in the channel the degradation of the streambed is minimal. There is also the added control of vertical degradation provided by the logjams. Although there ' is an abundance of trees and vegetative growth along the banks, there will be some amount of ban/: erosion. The added problem due to logjams is the shifting or possible change in channel location provided by a large log or group of logs that will become lodged in the main channel. ' EXISTING CHANNEL HYDRAULICS 1 1 1 lJ Hydraulic parameters for the existing Deep Creek channel are best defined for the dominant or channel forming discharge. The channel forming discharge is the steady discharge, which would give the channel the same morphology as a natural sequence of discharges. The channel forming discharge is also frequently referred to as the dominant, formative, effective or regime discharge, and can be defined as the discharge having hydraulic chazacteristics that forms and maintains the channel. In analyzing Deep Creek the dominant discharge or bankfull discharge roughly equates to a recurrence interval of a 2-year flood frequency. The hydrologic data provided by W WE used in the channel hydraulic study for the Deep Creek study reach aze as follows: Drainage Area (S Mi Mean Annual Runoff AF/Yr Flood Frequency (cfs) 2- eaz 5- ear 100- ear 4.0 1900 55.6 114. ] 180 ' Field observations from the June 19, 2000 site visit indicate a Manning's "n" of 0.065 for the channel. This "n" was further supported by values shown in the USGS Water-Supply Paper 1849, "Roughness Characteristics of Natural Channels." The width of channel at dominant ' discharge varied from about 3 to 15 feet. This would give an average width of 9 feet. The depth of flow for this width would be about 1.0 foot. The slope from Figure 1 is 0.049 fi/fi. With these ' Wright Water Engineers, Inc., 2490 W. 26°t Avenue, Ste. t00A, Denver, CO 80211 Tel. 3031480-1700; faz. 303/460-1020, e-mail:krwright~dwrightwater com