Hickory Grove Lake Watershed Improvements – Phase 1

Story County Conservation

Story County, Iowa

Hickory Grove Lake is a Story County Conservation (SCC) park that is a popular destination for recreation in central Iowa. The 400-acre park and 98-acre lake have popular campground amenities, a beach for swimming, and fishing opportunities. 

The lake was included on the Iowa 2008 303(d) impaired waters list due to high bacteria levels and is currently listed as “impaired” for sediment or nutrients. The lake suffered from deteriorating water quality due to siltation, as well as elevated nutrient levels leading to increasingly frequent and potentially harmful algae blooms. A Watershed Management Plan (WMP) was therefore completed by Iowa State University in March of 2013 that identified areas to reduce the impairment.

In February of 2014, FOX Engineering Associates, Inc. (FOX) worked with SCC staff to develop grant applications to the Iowa Department of Agriculture Watershed Improvement Review Board (WIRB) and the Iowa Department of Natural Resources (IDNR) Lakes Program.

Channel before

Channel before

FOX assisted SCC in developing a concept plan to restore 1,600 linear feet of stream channel upstream of the Lake; the channel was targeted as a significant sediment source in the WMP.  Significant gully erosion was also targeted in a branch of this channel and a grade stabilization structure (pond) was proposed to eliminate gully erosion. Concepts and costs provided to SCC were used for the grant application which requested approximately $423,000 of the total anticipated $598,000 project cost.  In March of 2014, SCC was awarded full funding from WIRB and the IDNR Lakes Program.

FOX began design of the project in July of 2014; this included the stream channel improvements on the area upstream of the lake, outside the Story County property, to the outfall of an existing drainage district tile outlet as described in the WMP.  Restoration and management of the stream channel upstream of the lake were determined to be important for enhancing or improving water quality for the lake. The stream channel had large quantities of bank and gully erosion because the riparian vegetation was no longer a viable source of channel protection.  The goal of the project was to restore the channel to a healthy stream environment.

A stream channel generally includes a variety of interacting plants and animals which have adapted to life in a water environment; a healthy stream includes plants and aquatic life which require oxygen, nutrients, and sunlight to flourish. There generally should be submergent and emergent plants in the stream which are important for aquatic animals to survive. Riparian vegetation is key to providing an environment that allows the stream channel community to flourish.

Adjacent farming practices associated with row-crop and livestock production were detrimental to the stream channel and caused significant degradation in the project area. This project focused on habitat modification and restoration within the riparian zone and employed a combination of methods to provide improvements.  In-stream treatments included pool excavations and bottom manipulation through the use of overpour structures and current deflectors.

Streamside modifications included livestock exclusion by fencing the project area, riparian buffer strips, and stream bank protection.  Limiting livestock access to streams protected the banks from damage and decreased soil erosion.  Off-stream watering was provided as a substitute for the pre-project in-stream watering. Fenced crossings were established to provide livestock the use of other areas of the property without affecting the stream channel. Buffer strips contained a variety of grasses to filter sediment, nutrients, and pesticides from the runoff before it entered the stream.

Channel after

Channel after

Tree removal and stream bank stabilization were provided to restore vegetated banks. Stabilization included riprap, rock cross-vane structures, turf reinforcement matting (TRM), and erosion control matting. An armored stilling basin at the tile discharge was installed to reduce erosion at the drainage district tile outfall location as well as to allow for lateral dispersion of the concentrated flows prior to entering the restored stream. Bank toe protection in the form of riprap and Curlex Blocs was employed throughout the channel length to limit channel toe degradation.

A one-acre grade stabilization structure was constructed on the channel branch to eliminate sedimentation of the lake caused by extensive gully erosion; it collects runoff and sediment from the upstream drainage area and sediment from the grade stabilization structure prior to being transported downstream to the lake.

A saturated buffer was installed on three drainage tiles that enter the channel by diverting the tile flows to a control box and through a saturated buffer system to reduce nutrient loading into the lake.

1.

Despite the heavy rains, the project reached substantial completion by the contract date of September 30, 2015.  The project channel area has been seeded and is stabilized with erosion control products.  Temporary seeding has been employed in remaining areas until dormant seeding can be completed.Design of the project was completed in April 2015 and the project received bids in May 2015.  Smith Seeding, Inc. was awarded the contract in the amount of approximately $403,000 and started construction in July 2015.  Construction continued through the summer with significant rains; over 20 inches of rain fell in the project area from July through September.  While the project was designed to be constructed in the typically lower rainfall months of summer, thereby reducing the risk of channel construction failures and limiting stream flows, the significant rainfalls were attenuated by project design Best Management Practices (BMPs) that greatly limited impacts to the channel and surrounding construction.

The project is currently under the contract cost and completion is anticipated in December 2015.

FOX Engineering is an environmental engineering firm based in Ames, Iowa. We specialize in water and wastewater solutions for our diverse municipal and industrial clients. Our work varies in size and scope and can be found throughout the Midwest and beyond.