Project Overview
The Trout Habitat Preservation Project (THPP) was the Brown’s Creek Watershed District’s first capital improvement project (CIP) installed in 2000 in the city of Grant. The project was designed to alleviate flooding surrounding a large land-locked basin while protecting the temperature sensitive resources of Brown’s Creek by directing lake overflows and direct drainage through a system of constructed wetlands and infiltration basins before reaching the headwaters of Brown’s Creek.
Project Benefits
In addition to flood prevention and reducing thermal loads to Brown’s Creek, the THPP provides benefits including:
- Runoff retention
- Increased wildlife and pollinator habitat
- Water quality treatment
- Groundwater recharge
Project Cost
Approximately $500,000 total:
- Legislative Commission on Minnesota Resources (LCMR): $250,000
- BWSR Wetland Road Replacement Program: $155,000
- Local Levy: $95,000
History
In the mid-1980’s, lake levels in the area began to rise due to regional groundwater level increases. Goggins, Plaisted, and School Section Lakes began to merge, forming a large shallow 440-acre basin. Surrounding homes and septic systems flooded, resulting in property damage and a threat to lake water quality. The BCWD, Washington County, the Department of Natural Resources, the cities of Stillwater and Hugo, May Township, and Trout Unlimited got involved to respond to residents’ requests for flood relief and resource protection. The THPP was proposed as a solution that would balance the environmental needs of Brown’s Creek with flood relief to the impacted properties.
The project included a detailed assessment of soils, geology, surface and groundwater hydrology, wetlands, and the behavior of the headwaters wetland complex that serves as the source of Brown’s Creek. The BCWD also investigated flood related impacts to different properties under different lake elevation scenarios. Finally, a detailed historical analysis of the original lake outlet was completed to determine if human influences were at least partly responsible for high lake levels.
Timeline
- 2001: Project Constructed
- 2004: Won the Minnesota Association of Watershed Districts (MAWD) Project of the Year Award
- 2006-2007: THPP Infiltration Recovery Project to improve infiltration capacity
- 2012: Prescribed burn
- 2016: Prescribed burn
System Design
The Trout Habitat Preservation Project was designed to minimize the discharge of warm summer lake water to Brown’s Creek, knowing that a traditional surface style outlet would not provide the level of protection needed. Designed by EOR, the THPP was an innovative approach including infiltration as a key component. The design included a lake outlet from the flooding basin and a series of wetlands and infiltration basins to store and infiltrate water, reducing the amount of water discharged to the headwaters of Brown’s Creek.
System Components and Operation
- Goggins Outlet: Transports discharge from the lake system when lake levels reach 970.5ft
- Pipe: Transports discharge from the lake system to Wetland B in the northwest corner of the site.
- Constructed Wetlands: Slows water, allowing sediment and attached pollutants to settle out.
- Wetland A: Collects runoff, which enters Wetland B at the southwest corner of the site.
- Wetland B: Collects water from the lake outlet and Wetland A, and discharges to Wetland C through a drop outlet structure with a 24” diameter round concrete pipe.
- Wetland C: Collects discharge from Wetland B and discharges into Basin 1 through twin arched round concrete pipes.
- Infiltration Basins: Fill and transport overflow between basins, allowing water to cool and be cleaned as it seeps back into the groundwater system and travels underground toward Brown’s Creek where it re-emerges as baseflow.
- Basin 1: Collects discharge from Wetland C and Basin 2. Water then infiltrates through the ground and infiltration trench. During high water events, water flows through a drop outlet structure with a 24” round concrete pipe into Basin 3.
- Basin 2: Water flows to and from Basin 1 through natural overflow at the 966ft elevation.
- Basin 3: Collects overflow from Basin 1 during high water events and discharges it to the headwaters of Brown’s Creek through a drop outlet structure with a 24” round concrete pipe
Operations and Maintenance
The THPP is a dynamic system which requires ongoing maintenance activities to ensure its long-term success. The site is entirely on private lands with an easement held by the Brown’s Creek Watershed District to maintain the facility around the grassy buffers of each wetland and basin. Operations and maintenance activities include regular monitoring and vegetative maintenance following CIP Standard Operating Procedures set forth by EOR. View the most recent THPP Inspection Report (PDF).
Monitoring
Monitoring of the THPP includes measuring infiltration rates and capturing seasonal water levels. Following construction, routine monitoring tracked the long-term performance of the THPP system. Monitoring from 2004-2006 indicated a reduction in infiltration within the system, resulting in the installation of an infiltration trench and equalizer pipe in Basin 1 in 2007. Ongoing monitoring occurs on a three-year basis to track the long-term performance of the system and infiltration trench.
Vegetative Maintenance
Vegetative maintenance of the THPP initially included the mowing of invasive species in affected areas and routine cutting of boxelder trees that sprouted up within the easement. Due to the size of the easement, it was decided in 2012 that prescribed burns every 3-5 years would be a more efficient method because they would improve the health and diversity of the restored prairie and reduce maintenance costs associated with annual mowing and spraying activities. The burns would be performed by a licenses contractor early in the spring when site conditions are favorable, and the contractor will obtain necessary permits to conduct the burn.
