Salt Creek North Tributaries and Creeks Watershed Master Plans
The City of Lincoln (City) and the Lower Platte South Natural Resources District (NRD) are in the process of developing a Comprehensive Watershed Management Plan for the City of Lincoln and its future growth areas. This comprehensive watershed plan is being developed basin by basin, through the completion of Watershed Master Plans for individual basins. Watershed Master Plans are used as planning tools to be referenced in conjunction with proposed development and as a guide in the preparation of future Capital Improvement Projects (CIPs).
The City and the NRD have previously adopted Watershed Master Plans for Antelope Creek, Beal Slough, Cardwell Branch, Deadman’s Run, Haines Branch, Little Salt Creek, Middle Creek, South Salt Creek, Southeast Upper Salt Creek and Stevens Creek. Figure 1 shows watersheds in the Lincoln area.
The Watershed Master Plans for Oak Creek, Lynn Creek and North Salt Creek (collectively referred to as the Salt Creek North Tributaries and Creeks Watershed Master Plans) are being prepared because future urban growth within these basins is expected as identified in the Lincoln-Lancaster County Comprehensive Plan.
The purpose of each Master Plan is to identify needed CIPs for stream stability and to quantify pre-development hydrologic conditions for sub-basins with potential near-term developments. Field inspecting all the streams in the three basins will identify areas of instability where, for example, the channel slope is steep, which can result in downcutting of the stream and accelerated streambank erosion. Urbanization of these basins may accelerate the downcutting if not addressed prior to development.
The Master Plans also investigate the potential effect of development on floodplains, delineate minimum stream corridors and identify special or unique areas in the watersheds for additional consideration to protect these areas.
The watershed study includes Geomorphic Field Investigation, Hydrologic and Hydraulic (H&H) Data Analysis, Land Use and Development, Minimum Corridor Mapping and identification of Special Areas within the watersheds. Each of these study components is considered in the development of potential CIPs. A summary of each component is provided below.
Geomorphic Field Investigation
The geomorphic evaluation is based on field reconnaissance of more than 110 miles of channel as shown in Figure 2. Geomorphic data are being collected during the months of February to May 2017. The goal of the field investigation is to provide reconnaissance level analysis of reach stability. Field data is being collected using the following data categories:
- Bank soil texture and coherence
- Average bank slope
- Average bank height
- Vegetative bank protection
- Bank cutting
- Mass wasting (wedge or slide slope failure)
- Bar development
- Debris jam potential
- Obstructions, flow deflectors and sediment traps
- Channel bed material consolidation and armoring
- Percentage of channel cross section constriction
- Sediment movement
The data categories are weighted and scored to provide an overall indication of stability for each data point. The data points are then summarized to provide an overall reach score, and an opinion of dominant process is also provided for each reach based on observations.
The following field data is collected at potential project locations:
Hydrologic and Hydraulic Data Analysis
The goal of the Hydrologic and Hydraulic Data Analysis is to provide a summary of the existing Hydrologic and Hydraulic (H&H) information available for these study areas. H&H data includes flow rates and depths of storm events for the streams and major tributaries located within the study area. Summarizing the data provides complete and updated data for design around these water features.
Land Use and Development
The Land Use and Development Analysis will study land use and known development plans in the watershed to evaluate the potential for effects on the existing floodplains. Approximations of possible future development will be based on current land use. Future development that could potentially affect the floodplain in areas containing estimated floodplain limits (identified as Zone A on FEMA maps) will be identified, prioritized and recommended for detailed analysis by a future study.
Minimum Corridor Mapping
Minimum corridor mapping will be performed for the study areas to identify the minimum stream corridors in the upper watersheds. The current minimum corridor identification methodology will be evaluated and potentially modified to allow for easier corridor mapping of waterways in other watersheds.
Identification of special areas in each watershed will be conducted to identify unique or special areas containing ecological, archeological, cultural and/or other community assets that merit consideration when developing CIPs. The following methodology is used to identify special areas within the watershed:
- Coordinate with the City, County and NRD to identify and locate the special areas.
- Obtain existing GIS files and identify previously generated reports containing information regarding the special areas.
- Develop GIS maps of the special areas and review existing documents and available data.
- Use the special area maps and data to evaluate what, if any, effect the Capital Improvement Projects might have on special areas and what measures need to be considered in the implementation of the CIPs to mitigate the potential effects.