Laserfiche WebLink
Project Design <br /> Channel and Floodplain Morphology <br /> Several factors went into the design of the proposed channel. First, the channel was designed to <br /> be analogous to the natural conditions observed in the reference reach. Second, the bed <br /> elevation at the confluence with Token Creek was located between the predicted channel bed <br /> elevation and the measured Token Creek bed elevation. This positioning will result in a <br /> 'hanging' channel,but this condition is typical of wetland channel confluences. The bed <br /> elevation will be the same as the existing channel at the upstream transition. Finally, the <br /> channel was designed to just contain the observed bankfull discharge (23 cfs) in the upstream <br /> reference reach. <br /> As a result of the change in elevation,we do see some overtopping of the banks at the 1.5 and 2 <br /> year flood discharges calculated in our hydrologic equations. The extent of the overtopping is <br /> greater near the tie-in point to the existing creek and nearly non-existent at the junction with <br /> Token Creek. The extent of overtopping is such that the water levels do not threaten the <br /> property but will allow some reconnection between the channel and immediate surrounding <br /> wetland in these areas. Figure 13 below shows the cross section of immediately below the tie in <br /> point with the existing creek under the bank-full, 1.5 year flood and 2 year flood conditions. <br /> raw- <br /> Proposed Channel Cross Section <br /> 1111111111111r <br /> 2 Year Flood Discharge <br /> 1.5 Year Flood Discharge <br /> Bankfull Discharge / E W <br /> faem <br /> Figure 13.HEC-RAS cross section of the proposed channel. <br /> Planform Geometry <br /> The planform geometry of the reference reach was used for the design of the proposed channel. <br /> Radius of curvatures between 22 and 42 ft were used with meander wavelengths between 214 <br /> and 294 ft and meander amplitudes between 118 and 146 ft. These criteria were integrated into a <br /> random number generator to create several iterations of proposed stream alignment between <br /> the tie-in point above the culvert to the junction with Token Creek. Use of these parameters and <br /> this approach insured a degree of heterogeneity consistent with natural streams. Given that the <br /> 15 <br />