2016-11-22_REPORT - M2011026 - Laserfiche WebLink

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Measured Parameter Upstream Downstream Upstream Downstream Restored Restored Reference Reference Sinuosity 1.13 1.13 1.16 1.11 Meander length (ft) 280 290 145 520 Radius of curvature(ft) 69 332 55 201 Belt width (ft) 50 45 60 110 Median Substrate Size" Small Cobble Small Cobble Small Cobble Small Cobble *Bankful Discharge from Manning's Equation: Q=(1.49/n)AR'/ S **Based on visual estimates Cross sectional data collected in 2016 indicate that Devil Creek varies significantly in natural geomorphology from the upstream reference station to the downstream reference station located at each end of the project area. Specifically,the upstream end of the project is located in a wider valley, and the stream has a larger cross sectional area compared to what was observed at the downstream end. As a result of the narrower valley,the downstream end of the project area also has less sinuosity. Additionally, the upstream end of the project area displays a higher bankfull discharge than the downstream end. The 2016 data indicate a stream channel more comparable to the downstream reference location. Field measurements indicate stream conditions that are more similar to reference conditions (undisturbed reaches of Devil Creek within project area) than to the preconstruction conditions of Devil Creek. Specifically, observed width/depth ratios have increased from 6.6 to 17.1 and 24.4 at the upstream and downstream cross sections, respectively. The increased width/depth ratio brings the stream channel back into conformance with the criteria for a Rosgen Type `B" channel (Rosgen, 1994). Conversely, baseline conditions indicate the channel was previously incised, as a width/depth ratio of less than 12 is typically not stable in streams with a sinuosity of less than 1.5. The increased width/depth ratios and decreased hydraulic radius indicate that more streamflow comes in contact with the bed and banks, increasing stream roughness, slowing stream velocities,and reducing erosive forces downstream of the restored reach. The stream measurements also indicate that the restored stream segment is moderately entrenched (i.e., entrenchment ratio is between 1.4 and 2.2), which is appropriate for a`B" type channel. Entrenchment ratios (i.e., width of the flood-prone area divided by the bankfull width) are anticipated to further increase upon the completion of gravel mining at the site and the subsequent removal of an erosion control berm constructed along the eastern (downstream left) bank of the stream. The purpose of the berm is to prevent sediment-laden stormwater from discharging into Devil Creek from the adjacent gravel operation, and is required by the site's SWMP. However, this berm also prevents floodwaters from Devil Creek from accessing this portion of its floodplain. When gravel operations adjacent to the restored segment of Devil Creek are completed, this berm will be removed, which will increase the storage capacity of Devil Creek's floodplain, increase the entrenchment ratio, and improve stream stability. 3.4.2 Wetland Hydrology As described in Section 2.2.4 above, wetland hydrology within MA-I and MA-5 was artificially influenced by adjacent gravel during the 2016 growing season. It is anticipated that MA-5 will receive artificial irrigation to facilitate germination of willows that will be replanted during the upcoming dormant For this reason, wetland hydrologic data (intended to record natural 2016 Wetland Mitigation Monitoring Report 12 December 2016 Keyah Grande Gravel Pit(060002) SME Environmental,Inc.