R2023-259 Resolution Authorizing Amendment No. 4 for Professional Engineering Services Agreement with Northwater Consulting for Lake Decatur Watershed Management Plan City Project 2019-38

Home Browse Search

Lake Decatur Watershed Management Plan—Phase V Scope of Services& Budget Task 5.10: Lake Sedimentation and Bathymetry Program The lake-wide bathymetric baseline mapping was mostly completed in Phase III, so no major activities are planned in 2024. Resurveying of sediment traps and select transects of the lake will occur in the second year of Phase V (2025). This will include the following: • Resurvey of three sediment traps and 6 cross-sections in the lake using motorized boat and XYLEM Sontek M9 Acoustic Doppler Profiler and GPS receiver. The M9 can profile bathymetry up to 40 m depth with 0.001 m depth resolution. HYPACK hydrological surveying software will be used to plan the survey to optimize results in key areas of interest and cross sections for follow-up monitoring. HYPACK will also be utilized to post-process the data and develop bathymetry profiles. Lake level transducers will be installed during the entire duration of the survey to record accurate lake levels,this is important to properly correct the survey data for changing lake levels throughout the duration the survey period • Analysis will be performed between the baseline surveys in 2021/2022 and the new survey in 2025. Sediment accumulation maps will be developed for the sediment traps with an estimation of rates. The 6 cross sections will be plotted comparatively to baseline conditions and include estimates of sediment accumulation and rates. Using the sediment traps and the 6 cross sections, lake-wide estimates of sediment accumulation will be made. Task 5.11: General Consulting Due to the diverse range of tasks and activities in Phase V, a general consulting task is included to efficiently support the City as needed in case out of scope engineering or environmental consulting is requested. For example, this may include some support with City-funded BMP projects or support with the lake monitoting data management and analysis. Task 5.12: Online Watershed Management System A custom watershed management system was configured for the Lake Decatur watershed in Phase IV. The Spatial Watershed Assessment and Management Model (SWAMM) is a custom web-based software that enables users to explore maps and spatial data from the completed subwatershed plans, analyze nutrient and sediment loading, perform cost-benefit analysis, and evaluate and track BMPs and scenarios to reduce nutrient and sediment delivery to the lakes. The interface allows for use of the watershed GIS data and watershed pollutant load model without the need for ESRI ArcMap software or knowledge of GIS. Standard SWAMM functionality includes: • Mapping portal to explore all areas within the watershed and toggle various datasets. • Ability to estimate nutrient and sediment loads from user delineated areas. • Ability to evaluate the effectiveness of BMPs for user delineated areas. • The ability to save proposed and completed practices into the system. • Management dashboard to see total loadings and visualize BMPs and progress towards reductions goals. 1 northwater