River-Lab

We conducted a post-project appraisal in November 2022 to evaluate the restoration’s performance using the goals outlined in the Sausal Creek Restoration at Dimond Park Monitoring Plan (Restoration Design Group, Inc. (RDG) 2017): restore native riparian habitat and improve channel stability. We performed vegetation surveys along the three transects (T1, T2, T3) initially defined by RDG and conducted a geomorphic survey along T3. We determined that the restoration project performed well in establishing native riparian habitat as we measured overall >90% canopy cover, which surpasses the percent cover criteria of 75% after five years of project implementation. Furthermore, we observed relatively high shrub survival rates of 138%at T1 and 173% at T2 and a limited shrub survival rate of 35% at T3. Despite meeting overall percent cover and survival rate criteria, we observed a decrease in native flora diversity, potentially due to excessive overstory shading from willows and invasive species outcompeting native plant species. Therefore, we recommend strategic thinning of willows, continued removal of invasive species, and additional replanting of native species. We compared the November 2022 channel geometry to previous years (pre-project, design, 2017, 2019, and 2021) and determined that the channel banks are stable (i.e., have experienced less than one foot of erosion). We also modeled the new channel geometry’s ability to convey a 10-year and 50-year storm event. Our model (HEC-RAS and the National Weather Service Normal Depth Calculator) results indicated that the channel would contain a 10-year event but not a 50-year event.