Geomorphic Evaluation Sample Clauses

Geomorphic Evaluation. The geomorphic evaluation task will include study of historical air photos, maps, bridge condition surveys, and other relevant material to understand the types of channel changes that have occurred and the potential cause. It will also involve a geomorphic field assessment of the project channel reach to identify areas with bank instabilities and lateral channel migration, features in the stream bed and bank forcing the plan and profile of the stream, locations and causes of sediment deposition and scour, changes in grade and sediment size. Typical hydraulic geometry upstream and downstream of the bridge will be measured, including active channel and bankfull widths and depths. The project geomorphologist and engineer will survey typical cross sections and extend the longitudinal profile of the channel thalweg beyond the length collected as part of the project topographic survey. Office analysis conducted as part of this effort will include evaluation of the channel profile to identify the current overall stable grade of the channel. The profile analysis will determine if the existing bridge crossing is functioning as a kick-point in the overall channel profile and preventing upstream incision, or only causing localized aggradation. It will also include estimating the low and high vertical adjustment potential of the channel bed over the service life of the new bridge, predicting channel response associated with changes in profile resulting from any proposed realignment, and determining if in-channel grade control is needed as part of the project. Other analysis will include calculation of channel width-depth ratios, sinuosity verses channel slope, bankfull discharge and discharge required to mobilize the characteristic sediment size transported by the channel. Bank shear stress will also be evaluated relative to maximum allowable shear stress for various types of stabilizing vegetation to evaluate effectiveness of different types of bioengineering bank stabilizing solutions.