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Watershed Stormwater Master Plans: South Tributaries Watershed Study

Study Overview


Study Overview

The Watershed Master Plans (Master Plans) for the Haines Branch Watershed, Middle Creek Watershed and South Salt Creek Watershed are being prepared because future urban growth within these basins is expected as identified in the City of Lincoln-Lancaster County Comprehensive Plan. The purpose of the Master Plans is to identify needed CIPs for water quality and stream stability and to quantify pre-development hydrologic conditions for sub-basins with potential near-term developments. The Master Plans also identify special or unique areas in the watershed, and additional consideration was given to protecting these areas.

The project team is led by the City and NRD in cooperation with Lancaster County. The City and NRD retained the consultant team of Intuition & Logic (I&L) in association with Heartland Center for Leadership Development and the U. S. Geological Survey to provide assistance with the planning effort.

Study Methodology

Natural Rock Riffle on Haines Branch
Natural Rock Riffle on Haines Branch

The Haines Branch Watershed, Middle Creek Watershed and South Salt Creek Watershed plans include hydrologic modeling of select sub-basins, water quality investigation, geomorphic field investigation and identification of special and unique areas within the watershed. Each of these study components was considered in the development of potential CIPs. A summary of each component is provided below.

Hydrologic Modeling

The goal of the hydrologic modeling is to identify predevelopment flow rates for areas under development pressure. The predevelopment hydrologic data will provide developers information necessary to design site stormwater amenities.

Water Quality Investigation

The water quality investigation consists of performing water quality sampling at ten locations in the watershed. The purpose of the water quality sampling is to gather dry and wet weather water sample data along the main channels. The goal is to collect two dry weather water samples and one wet weather water sample and test the samples for the following:

  • Total suspended solids
  • Total phosphorous
  • Magnesium
  • Calcium
  • Sulfate
  • pH
  • Dissolved oxygen
  • Temperature
  • Hardness
  • Conductivity
  • Selenium
  • Ammonia
  • Total organic carbon
  • Copper
  • E. Coli

Geomorphic Field Investigation

Streams Walked Within the Three Watersheds
Streams Walked Within the Three Watersheds

The geomorphic evaluation is based on field reconnaissance of 130 miles of channel as shown in the figure to the right.

Geomorphic data were collected during March and April 2013. The goal of the field investigation is to provide reconnaissance level analysis of stream stability. Field data was 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
Steep Bank Erosion
Steep Bank Erosion

The data categories are weighted and scored to provide an overall indication of stability for each data point. The data points were then summarized to provide an overall reach score and an opinion of dominant process for each reach based on observations.

Field data was also collected at potential project locations. The following field data was also collected for potential observed projects:

  • Project type (bed stabilization and/or bank stabilization)
  • Project length
  • Brief problem description
  • Brief recommended solution description
  • Additional notes as needed

Special Areas Consideration

Identification of special areas was 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 was used to identify special areas within the watershed:

Perched and Damaged Infrastructure
Perched and Damaged Infrastructure
  • Coordinate with the City, County and NRD to identify and locate known special areas.
  • Obtain existing GIS files, and identify previously generated reports containing information regarding known special areas.
  • Develop GIS maps of the special areas, develop a list of the areas and what existing documents and data are available, and review the documents to extract information regarding known special areas.
  • Use the special areas maps and data to evaluate the effect that developments might have on special areas and what measures need to be considered for developments to mitigate their potential impacts.
Validate

South Tributaries Watershed Study