North Raccoon

WMC Watershed

Plan

Client

North Raccoon WMC

Location

Storm Lake, IA

Size

2,470 square miles

One watershed, one community charting its own destiny through shared responsibility and common goals. Working together for reduced flooding, improved water quality and soil health, enhanced education and strengthened community.

Civil Engineering & Water Resources

This planning effort was pursued in response to recent destructive flood events across the state. According to the Iowa Flood Center, Iowa has seen 18 billion dollars in flood damage over the last 30 years (Arenas Amado et al. 2018). The floods of 2008 in Iowa resulted in the sixth-largest FEMA disaster declaration ever (to date), based on estimated public financial assistance (City of Cedar Rapids 2020). Such flooding events are becoming more frequent in the state.

Low-income, marginalized and socially vulnerable populations are only as resilient as the social resources available, yet a community’s flood resilience is only as strong as its most vulnerable populations. Flooding impacts both the well-being of communities in the watershed as well as the economic capacity of vulnerable communities to protect their residents.

High nitrate levels and pathogen levels in surface and groundwater supplies pose potential risks to local drinking water supplies. Impacts on Des Moines Water Works operations have been well publicized. However, two other communities, Dawson and Lake View, have had impacts due to high nitrate levels. Nearly 80% of the wells throughout the watershed have been identified as highly susceptible. In addition, bacteria contamination has been noted in numerous private wells. In total, over 300 private wells across the watershed have found elevated levels of nitrate or bacteria.

The North Raccoon River Watershed is located in Central and West Central Iowa. The stream and river network generally flows from northwest to southeast, reaching the confluence with the South Raccoon River near Van Meter. From there, the Raccoon River flows easterly towards Des Moines, where it merges with the Des Moines River, which is the downstream end of this watershed planning area.

In the North Raccoon River Watershed:

There are 12 waterbodies where primary-contact recreational uses are impaired due to elevated bacteria levels.

There are 10 waterbodies where conditions to support aquatic life are impaired due to a variety of factors: turbidity, algal growth and biological.

These conditions can prevent public use of existing resources for recreation. They can also impact the desire to expand the network of other recreational opportunities (such as the Central Iowa Water Trails network). In addition to recreational impacts caused by sediment noted previously, high levels of sediment runoff can reduce storage volumes in lakes, wetlands, ponds and other stormwater storage practices. This can lead to costly dredging or soil-removal operations. High levels of sediment can also cover rock and cobble areas which may be used as habitats for fish and invertebrates. Deposition in channels along inside bends can also accelerate stream migration, an erosive process that itself generates sediment. Deposition can accelerate the movement of outer bends in an outward (and generally downstream) direction.

High nutrient levels can lead to the growth of algae and other organisms that can reduce oxygen levels in water bodies. When populations of these organisms die off, the process of decay consumes oxygen. If levels fall too low, aquatic life in those areas can be fatally impacted. Some species may be able to swim to areas with better oxygen levels. Slow-moving aquatic life may not be able to move fast enough to survive (NOAA 2020). These conditions can sometimes be present in Iowa streams and lakes. However, a large hypoxic “dead zone” has formed in the Gulf of Mexico, where dissolved oxygen levels are less than 2 mg/L. This area is now the second-largest “dead zone” in the world. This has led to a national effort to reduce the size of the dead zone to 5,000 square kilometers (1,930 square miles). The size of the dead zone varies from year to year due to weather conditions. Over the last five years of measurements (2014–2019) the zone has measured between 7,000 and 22,700 square kilometers (2,700 to 8,800 square miles). Those national efforts led to the formation of Iowa’s NRS to address nitrogen and phosphorus pollution (U.S. EPA 2015).

Watershed Area Assessed

2,470 SQM

Subwatersheds Encompassed

75 HUC-12

From Iowa Involved

13 Counties

Land uses and natural resources across the watershed, watershed climate and streamflow patterns, flooding impacts, water quality issues, designated uses of streams and lakes, and how those uses have been impaired are only some of the watershed properties investigated as part of this study. To study these properties, the North Raccoon River Watershed has been divided into six distinct "watershed settings" which are used to group areas that share similar properties or challenges.

This watershed plan offers a high-level vision of the path toward reaching watershed goals. This vision needs to be translated down into smaller subwatersheds to identify and prioritize specific project sites. Then, direct interactions with landowners, producers and regulatory agencies will be needed to carry a practice from an idea into reality.

In some cases, there will need to be updated or new local ordinances or requirements to implement this plan. However, “policies” do not necessarily refer to regulations. It also refers to things that members and partners may need to advocate for financial assistance, or other help from federal or state agencies.

Many methods are available to address priority flooding and water quality issues of the North Raccoon Watershed, but no single approach reaches all goals and objectives of this plan. This is an overview of some of the broad sweep of practices available to help achieve goals. Ultimate choices depend on local knowledge and experience, physical conditions and the specific goal or project intent.

This estimate includes the public and private financial resources that will be needed to carry out the first 20 years of implementation (2020–2039). In total, it is projected that $184 million (2020 dollars) will be needed to carry out implementation during this period. This includes the costs for: Operational framework, Flood planning, Water quality conservation practices, Flood and water quality monitoring. Members and partners will have additional costs related to flood repairs and risk-reduction efforts.

This plan should be considered a “living document,” changing direction as needed to include new research and results, applied toward the ultimate project goals.

Increases in precipitation will yield hydraulic response in waterways. Larger and more frequent storm events will likely increase channel erosion and sediment loading. However, the years immediately following this study have been characterized by drought.

Rapid urban development in communities like Waukee and West Des Moines makes Dallas County one of the fastest growing counties in Iowa. Developing agricultural land for urban uses disrupts the existing hydrologic cycle but stormwater management can mitigate this change.

The NRRWMC (North Raccoon River Watershed Management Coalition) decided to make flooding and water quality the primary issues for this plan to address. Strategies to address these goals include quantifying practices and estimating costs to achieve a set benchmark. After considerable discussion, the NRRWMC decided to adopt the nitrate reduction determined by the Raccoon River TMDL (48.1% reduction from point and non-point sources) and the phosphorus-reduction target established in the Iowa NRS for non-point source pollution (45% reduction total, 29% assumed for non-point sources).

The NRRWMC chose to consider pathogens—represented by Escherichia coli (E. coli) bacteria—and sediments as secondary issues for this plan to address. However, no numeric reduction objectives would be established for these issues, due in part to the complex nature of fully implementing practices and monitoring performance to address these pollutants.

The NRRWMC will need to grow in unity and find financial resources to implement this plan. They will need to be organized as a group and seek to expand the list of active partners who will be acting and advocating for additional outside support.

View the North Raccoon WMC Watershed Plan.