Brown’s Creek is one of the few remaining cold water fisheries in the Metropolitan Area; however, it is impaired due to high suspended solids and high temperatures. To understand the extensive and complex in-stream temperature and local climate data already collected by the Brown's Creek Watershed District, BCWD received a 2014 Clean Water Fund Grant for $33,500 to facilitate the development of a thermal model to determine thermal sources and cost-effective management projects and practices to reduce thermal loading to Brown's Creek.
Thermal Model Details:
The thermal model will use physics-based computer models to understand the existing temperature conditions and to project future conditions for different BMP implementation scenarios. This work will be conducted by expert stream temperature modeler William Herb, Research Associate at the U of MN St. Anthony Falls Laboratory as follows:
1. Field Data Analysis – Existing stream temperature, flow, groundwater and climate data will be examined to characterize temperature exceedances under different flow and climate conditions, utilizing 4 years of temp data, 3 years of local climate data from the BCWD weather station and 11 years of groundwater data.
2. LiDAR Analysis. High resolution LiDAR data will be used to characterize the main-stem channel of Brown’s Creek (channel width and shape, riparian vegetation height and density) in the model.
3. Stream Temperature Model – A stream temperature model for Brown’s Creek will be assembled and calibrated using the USGS Stream Network and Stream Segment Temperature Model (SNTEMP). This model will generate continuous simulation of daily average, maximum and minimum stream temperature for Brown’s Creek. The sensitivity of stream temperature characteristics, such as exceedance frequency, to changes in riparian shading and groundwater inputs will be determined, and future temperature conditions will be projected for several future scenarios such as increased riparian shading or reduced groundwater inputs.
4. Thermal Source Models – Models for impervious areas, detention ponds and/or wetlands will be assembled using previously developed SAFL models. Heat loadings to Brown’s Creek from these sources will be estimated using continuous simulations over several years, to include a variety of climate conditions. Reductions in thermal loading will be estimated for a variety of BMP implementation projects (e.g. riparian shading and/or pond retrofit projects) to prioritize the most cost-effect projects.