The Fourmile Creek Watershed is 76,600-acres consisting of urban and agriculture communities. It is currently home to over 80,000 people. The watershed’s northernmost reaches begin near the town of Slater. The largest area of the watershed is located in Polk County and encompasses the cities of Sheldahl, Alleman, Elkhart, Ankeny, Bondurant, Altoona, Des Moines and Pleasant Hill.
Fourmile Creek and its tributaries run for over 40 miles before draining into the Des Moines River. Along its path, the creek has a long history of extreme flooding, erosion, and poor water quality. To address these diverse issues, local communities created one of the first watershed management authorities (WMA) in the state in 2012. This WMA focuses on collaborative work to address flooding and water quality.
The primary focus within Fourmile Creek is to reduce flooding. With growing urban areas and increasingly common large storm events, flooding continues to cause damage in the watershed. To mitigate this damage, ongoing efforts focus on holding water in upland areas of the watershed, by utilizing practices such as regional detention basins and wetlands. Policy changes are recommended within urban areas of the watershed. Preserving stream buffers and floodplains protects urban residents and allows mother nature to function as intended.
Fourmile Creek has several water quality issues including excess nutrients, sedimentation, and bacteria. Across the watershed work must be completed in both urban and agricultural areas to improve water quality. In rural areas efforts are underway to partner with farmers to increase the adoption of practices such as cover crops, reduced tillage, and stream prairie buffers. Within urban areas, cities and homeowners must focus on treating stormwater runoff. Residents can make simple changes such as picking up pet waste (bacteria) and reducing fertilizer use. They can utilize cost share programs to reduce runoff by installing rain gardens and soil quality restorations. Cities and counties must also work together to reduce runoff and stabilize eroding sections of stream.
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Policy guides how stormwater management techniques are used to mitigate the impacts of urban development. The Fourmile Creek Watershed Management Plan recommends altering development standards for more effective stormwater management. These policy changes include, regulations protecting stream buffers, floodplain ordinances that reduce flood risks, and the implementation of best management practices as outlined in the Iowa Stormwater Management Manual.
The Fourmile Creek Watershed is located in the Des Moines Lobe landform region, near the
southern terminus of this lobe that formed during the Wisconsin Glaciation between
12,000 and 15,000 years ago. Glacial activity, other climatic events, and land use practices that followed the last glaciations have shaped the landscape, contributing to carving a more defined Fourmile Creek stream channel. This region has mostly level terrain and occasional bands of crooked ridges. Marshes and ponds are found between these ridges and generally, have no natural drainage outlets. The landforms found in the watershed are ground moraines on uplands, and flood plain and stream terraces. As a result, the upper portions of the watershed have pothole characteristics, which provide depressional areas that pool runoff and help regulate flows. The lower portion of the watershed is characterized by a gently to moderate rolling landscape, such as in the Des Moines, Altoona, and Pleasant Hill areas.
Primary land use varies across the Fourmile Creek Watershed.
Historic Monitoring Reports
Historically, monitoring on Fourmile Creek was done through the IOWATER program, a voluntary water monitoring program supported with expertise and resources through the IDNR and local partners, and results were obtained from Mary Skopec, IOWATER Program Coordinator and Research Geologist. Field measurements were taken for nitrate, nitrite, phosphorous, chloride, dissolved oxygen, and water transparency. Laboratory tests were also run for nitrate, nitrite, orthophosphate as P, total phosphate as P, turbidity, E. coli bacteria, bromide, fluoride, ammonia nitrogen as N, sulfate, and total coliform
bacteria. There are 10 monitoring sites along Fourmile Creek and each was sampled one to
two times per year from 2004 to 2009 and monthly starting in 2010.
The general findings of the analyzed data are as follows:
Based on the monitoring results, the pollutants of concern in the watershed were
prioritized by stakeholders and the WMA. These include groups of both primary and
secondary pollutants. Primary pollutants include sediment and bacteria and secondary
pollutants include phosphorous and nitrogen. Although the Rapid Assessment of Stream
Conditions Along Length (RASCAL) and Revised Universal Soil Loss Equation (RUSLE)
assessments provided ample information on a watershed level, monitoring data can provide targeted information on a local level for priority areas to implement water quality projects. Currently, there is inadequate monitoring data available for the needs of this plan. This proves difficult to determine the origin of the pollutants and quantities present. More robust monitoring of these parameters is addressed in a later
Sediment loading and bacteria levels were prioritized as the primary pollutants in the
Fourmile Creek Watershed because of the recreational contact concerns. Even though
Fourmile Creek is not a drinking water source, there is still a pollutant concern due to
human contact with the water.
Sources of sediment loading could be from any combination of streambank erosion and
stormwater runoff from the surrounding rural and urban land uses. Excess amounts of
sediment can cloud the stream and harm underwater organisms.
Sources of bacteria could be from any combination of pet waste, wildlife, agriculture,
Leaking, or overflowing septic systems and failing infrastructure. Bacteria levels can
fluctuate greatly based on storm runoff, leaking sewage lines, the time of day, and the time of year. Elevated nutrients and water temperatures also influence bacteria levels, causing health risks to anyone encountering the water.
Phosphorous and nitrogen were set as secondary constituents of concern in the Fourmile
Creek Watershed, since Fourmile Creek is not a drinking water source but high levels of
these pollutants have a negative impact on the stream. These nutrients are essential for
plant and animal growth and naturally abundant in the environment. Elevated nutrient
levels can cause overstimulation of growth of plants and algae. Overgrowth can cause
decrease dissolved oxygen in a stream, block light to deeper water, and clog water intakes. Both constituents are being considered for further monitoring and mitigation, if and when funding would be available.
A comprehensive stream assessment was completed by the PSWCD using the Rapid
Assessment of Stream Conditions Along Length (RASCAL) tool, which is one way to gain
firsthand knowledge of the existing conditions in a stream. This tool allows priority areas
in the stream to be identified for targeted conservation practices. These practices would
reduce pollutant loading by amending adjacent land use, restoring habitat, and stabilizing
banks. Data was collected including observed gullies, exposed utilities, tile outfalls, and
storm sewers. A GPS camera was frequently used to document these points of interest and
keep track of stream conditions.