02/23/2022 EB Packet - Laserfiche WebLink

Home Search

A Proposal for Lake Amelia Subwatershed Management Plan for the City of Lino Lakes | 2 Task 3 –Water Quality and Drainage (H&H) Modeling (40 hours $5,000) To assess the existing conditions, WSB plans to develop two models: -A drainage model to assess the surface water bounce during wet seasons and critical rainfall events (2, 10, 100-yr, 24-hr precipitation and 100-yr, 10-day snowmelt events). -A water quality model to assess the pollutant transport into Lake Amelia. (Total Phosphorus (TP) in particular). Subject to City and VLAWMO preference and recommendations, the drainage model will be developed using HEC-RAS software. HEC-RAS provides reliable computations, good visualization, and two-way data portability with GIS. HydroCAD will be used to estimate flow rates to the ditch for the critical events using the SCS curve number method, and checked against the flow monitoring in Task 2. For the water quality modeling, WSB will use P8. Land use information gathered in the Wilkinson Lake TMDL study along with the other land use data in the drainage area will be used to determine pollutant loading. Information gathered from the flow monitoring and water quality sampling will be used to update the modeling and show the most current pollutant loading. WSB will use the existing models as a baseline to determine a minimalist, hybrid, and full-build scenario. Once the models have been completed, the results will be summarized and sent to the City and VLAWMO to be discussed. The second meeting will discuss the results of the models and refine strategies for developing the future corridor concepts including phasing options. Task 4 – Ownership Phasing (10 hours $1,200) A key element in the transition is the ownership transfer from the current residents and developers into public domain. Ideally, as part of this transfer, the existing ditch corridor will become public domain. Likely a phased approach of gaining ownership of the corridor will be implemented, including acquisition upon redevelopment, and obtaining easements from existing property owners. WSB will document the formal legal steps and permitting needed to accomplish: (a) easement acquisition along the private ditch, and (b) future transfer into the public domain of the entire corridor. Task 5 – Surface Water Improvement Options (38 hours $4,300) Based on the ownership transition phasing discussed in Task 4, WSB anticipates three improvement concepts including a minimalist, hybrid, and full build scenario. Minimalist Scenario: This assumes drainage easement acquisition along the ditch but no ownership transfer in the initial phase. This will allow for immediate access to the corridor to address current ditch failures and to begin to resolve the drainage concerns. WSB will identify the measures needed to stabilize the slope along with improving stormwater conveyance. This option will focus solely on in ditch improvements to repair erosion, stabilize slopes, and improve the function and drainage of the ditch to reduce localized flooding and inundation to adjacent properties. Hybrid Scenario: In this scenario, WSB will explore options for enhancement outside of the streambank either within obtained easements or publicly owned land. This includes streambank regrading, conveyance improvement, expanding existing wetland perimeters, and constructing stormwater BMPs. This option looks more in-depth at water quality improvements and pollutant load reductions within the corridor. Full Build Scenario: This scenario assumes the broader corridor will redevelop, and the ditch will become public domain. This scenario envisions a comprehensive transformation of the existing drainage ditch into a naturally looking channel corridor of enriched bio-habitat, improved water quality and enhanced aesthetics. WSB will explore the creation of a wider meandering corridor designed to maximize these functions. This concept may include an in-channel vegetated bench to maximize pollutant removals, along with potential wetland banking and floodplain restoration. A third meeting will be scheduled to discuss the improvement concepts in terms of feasibility, benefits, challenges, and costs. An intermediary concept may emerge from discussions with the City and VLAWMO. Task 6. Improvement Concepts Evaluation – Pollutant Load Reduction and Cost Estimates (16 hours $2,000) Once the improvement concepts are established, WSB will proceed with a detailed evaluation of the pollutant load reduction, hydrology and hydraulics model, and cost estimates. The cost estimates will be CIP style estimates and can be used later for budgeting and grant funding.