Polk Soil and water conservation district
The Solution
Strategies for watershed protection in urban areas
Policy
- Stop developing in floodways. Instead use these areas as greenways.
- Collaborate with agricultural interests, through watershed management authorities, to develop watershed management plans that benefit stakeholders throughout the watershed and reduce downstream flood potential.
- Work with cities, through watershed management authorities, to develop watershed management plans that benefit stakeholders throughout the watershed and reduce downstream flood potential.
Unified Sizing Criteria
Traditional stormwater management focuses on large storm events, to reduce impacts of large flooding events. While this is important, these structures do not address water quality concerns or smaller storm events causing excessive streambank erosion in urban areas.
When planning and designing for post construction stormwater management, considerations should be given to both water quality and water quantity (flood control).
The Unified Sizing Criteria in the Iowa Stormwater Management Manual (ISWMM) provides a comprehensive approach to managing stormwater, from the more frequent, smaller rainfall events to the less frequent flooding events.
Water Quality Volume (WQv)
Treats runoff from the 1.25 inch or less rainfall, which is the most frequent rainfall in Iowa. Managing this size of event helps reduce the most pollution.
Channel Protection Volume (CPv)
Manages the 1-year, 24-hour duration event. Managing this size of storm reduces bank full flows and helps minimize downstream channel erosion.
Overbank Flood Protection (Qp)
Provides peak discharge control for the 5-year, 24-hour duration event. Managing this size of storm prevents downstream capacity issues and minimizes localized overbank flooding.
Extreme Flood Protection (Qf)
Manages the 100-year, 24-hour duration event. Managing this size of storm minimizes extreme flooding downstream. Flood management typically occurs through detention controls and/or floodplain management. Constructed wetlands and other practices can also be effective techniques. Most communities adequately mange the Qp and Qf. In order to improve Iowa’s water quality and provide additional protection form flooding, further management of the WQv and CPv is needed.
Education and Outreach
- Expand educational efforts to help people understand their hydrologic footprint and ways they can contribute to water quality protections. For instance:
- Prevent pollution from oil and grease by keeping vehicles in good working order.
- Don’t dump or discharge pollutants into storm sewers or leave grass clippings on the landscape.
- Use phosphorous-free fertilizers.
Stormwater Practices
- Stop developing in floodways. Instead use these areas as greenways.
- Collaborate with agricultural interests, through watershed management authorities, to develop watershed management plans that benefit stakeholders throughout the watershed and reduce downstream flood potential.
Soil Quality Restoration
The process of improving soil health on new or existing lawns. The process uses tillage, aeration, and compost to increase infiltration and organic matter content. Soil quality restoration leads to healthier soils that can absorb more rain.
Native Landscaping
Native plants should be strategically placed in the landscape to enhance infiltration of stormwater. Their extensive root systems hold soil, slow runoff, and improve infiltration. The plants also absorb nutrients, such as nitrogen and phosphorous, and don’t require fertilizer, pesticides, or supplemental water to survive after establishment.
Rain Gardens, Bioretention Cell, Bioswale
Engineered vegetate landscape features built to capture runoff from impervious surfaces and filter pollutants from runoff. They treat small storms, while runoff from lager storms flow to storm sewers or larger regional conservation practices.
Detention and Retention Basins
These are sized to store and slowly release stormwater to alleviate downstream flooding. They can also be designed to manage small storm events to improve water quality, reduce streambank erosion, and provide flood control.
Permeable Pavers
This pavement system us used in place of traditional concrete or asphalt to decrease stormwater runoff. Unlike traditional surfaces, permeable pavers allow stormwater to seep through the joints in the pavers and enter the spaces in the gravel below. Water then moves into the soil or slowly into a stormwater drain.
Stormwater Wetlands
Used both for water quality and flood management, constructed wetlands provide a permanent pool of water which varies in depth. The collection area provides temporary storage, removal of pollutants, and habitat for wetland plants and wildlife.
Funding Mechanisms
- Support state and federal funding for conservation programs that provide financial assistance for the adoption of practices that hold more water in the uplands.
- Create 28E agreements that help fund the installation of practices in watersheds above cities that provide downstream flood protection and improve water quality.
- Create stormwater utilities and utilize part of the revenue stream for local cost-share programs that help reduce flooding and protect water quality.
- Encourage the use of the State Revolving Loan program for stormwater management practices.
- Learn more about available cost-share within the Des Moines Metro area at raincampaign.org
Strategies for watershed protection in Rural areas
Watershed Management Authorities
In 2010, Iowa lawmakers passed legislation authorizing the creation of Watershed Management Authorities (WMA). A WMA is a mechanism for cities, counties, Soil & Water Conservation Districts, and stakeholders to cooperatively engage in watershed planning and management. Four WMAs have formed in the Des Moines metro area- Fourmile Creek, Mud/Camp/Spring Creeks, Walnut Creek, and Beaver Creek.
Many communities have seen the value of working together to develop watershed management plans and unifying policies that will improve and protect water quality in the region. During the planning process, high priority goals were set utilizing public and stakeholder input. Specific strategies are found throughout the plans to show what steps the urban and rural stakeholders can take to reach these goals. Strategies range from policy and ordinance changes to conservation practices. Watershed scale planning efforts have also shown communities the benefit of working with farmers to make improvements on the agricultural lands.
Watershed plans have been complete for three of the metro WMAs (Fourmile, Walnut, Mud/Camp/Spring Creeks). With plans complete WMA boards are proceeding to implement their plans. To achieve the lengthy list of goals, the jurisdictions within each of these WMAs pooled their resources to hire a watershed coordinator. The jurisdictions chose to have the Polk Soil & Water Conservation District move forward with WMA coordination. Polk SWCD provided leadership during the formation and throughout the watershed management planning process with the aid of Urban Conservationist, Jennifer Welch. Now Polk SWCD staff are working one on one with cities, farmers, partners, and others to implement the watershed management plans
Beaver Creek
The Beaver Creek watershed covers 244,347 acres in Polk, Dallas, Boone, Green, and Webster counties. The creek and its tributaries run for over 100 miles before joining with the Des Moines River. Many jurisdictions are located within the watershed boundaries including: Boxholm, Dana, Ogden, Beaver, Grand Junction, Berkley, Woodward, Bouton, Perry, Granger, Minburn, Dallas Center, Grimes, Johnston, Urbandale, and Des Moines.
The landuse within the watershed is dominated by agriculture with only a small urban area located in the southern reaches. Flooding, high nutrients, and high levels of sediment are the main issues seen throughout the watershed. A Watershed Management Authority is being created to address these concerns and determine methods of action to overcome them.
Four Mile Creek
The Fourmile Creek Watershed is a 76,600 acre watershed (HUC 10 – #0710000801) consisting of urban and agriculture communities. The watershed’s northernmost reaches are located in Boone and Story Counties and include portions of the cities of Sheldahl and Slater. The largest area of the watershed is located in Polk County and encompasses the cities of Pleasant Hill, Ankeny, Altoona, Alleman, Elkhart, and Des Moines.
Fourmile Creek and its tributaries run for over 40 miles, beginning in northern Polk County and eventually joining with the Des Moines River in southern Polk County. Resource concerns seen in and along the creek include high bacteria levels, excess nutrients (nitrogen and phosphorus), and erosion. A Watershed Management Authority (WMA) was formed to try and address these concerns. A watershed management plan was completed by Snyder and Associates and will be used to improve the watershed and address the environmental concerns.
Mud, Camp, Spring
Mud, Camp and Spring Creeks are located in Polk, Jasper, and Marion Counties. Together, the creeks and their tributaries traverse over 50 miles and their watersheds cover 64,511 acres. While most of the land use in the watersheds is agricultural, there is a large potential for development in the coming years. Cities like Altoona, Bondurant and Pleasant Hill are rapidly expanding into the watershed already.
Because of the large agricultural area in the watersheds, high levels of nutrients and sediment entering the water is a main concern. Flooding, nutrient pollution, and stream bank erosion are the primary concerns in the watersheds.
North Raccoon River
The Walnut Creek Watershed is located in western Polk and eastern Dallas counties in central Iowa. The 53,000 acre landscape is rapidly changing, with over six-square miles being developing between 2001-2011. The creek itself is a primary source for the metro area drinking water, joining up with the Raccoon River just above Des Moines Water Works.
A Watershed Management Authority (WMA) was developed to address environmental concerns seen throughout the watershed and in the creek. A watershed management plan was developed by the WMA to showcase ways the urban and rural communities can overcome these concerns and increase the overall quality of the watershed.
Green Infrastructure and Greenways
Green Infrastructure
To protect water quality and quality of life, communities must also protect green infrastructure- the interconnected network of open space and other natural areas. Green infrastructure is an integrated landscape approach and a conservation strategy that recognizes the interactions between the built environment, rural lands, and native ecosystems.
Communities can retain an interconnected network of waterways, wetlands, prairies, woodlands, wildlife habitats, and natural areas. If not protected during development, these areas and their functions are lost. Protecting green infrastructure provides a “treatment train” that reduces the volume of runoff generated and can be used to protect water quality.
Without green infrastructure and design techniques to manage runoff differently, the storm water moves rapidly to storm sewers and into streams and rivers without any treatment, increasing flooding and reducing water quality. This often results in the use of costly engineering solutions for problems that can be avoided or mitigated by protecting intact natural resources, so they do not lose their natural function. If protected, as water moves through a treatment train outlined in the natural resources inventory, it is filtered through infiltration, and peak flows are reduced and delayed. A major component of the natural resources overlay district will be to lay the groundwork for future adoption of green infrastructure methods. A developed plan outlining valued resources is a vital step towards future protection from development.
Greenways
Sometimes green infrastructure is protected through other mechanisms, such as greenway development.
A greenway is a linear corridor of open space along a waterway, promoting public health, safety and general welfare through flood protection and water quality improvements. Greenways are intended to be land protected for environmentally sustainable purposes and may include passive recreation and educational amenities, cultural resources, urban agriculture, conservation, and non-vehicular transportation.
Rural Practices
- Use no-till farming to improve soil quality and increase the landscapes ability to absorb more rain.
- Install contour buffer strips to help absorb runoff.
- Retire highly erodible land with low profitability through the Conservation Reserve Program. Reconstruct prairie areas to improve soil quality.
- Construct ponds and wetlands that hold and slowly release water to reduce downstream peak flows.
Nutrient Reducing Practices
Conservation practices that reduce the amount of nutrients such as nitrogen and phosphorus that enter surface waters. Bioreactors and saturated buffers are used to remove nitrates from underground tile water before it enters a nearby stream or pond. Strips of perennial vegetation (filter strips) are placed along water sources to intercept surface water runoff, removing excess nutrients.
In-Field Practices
Upstream Retention Sturctures
Pond and wetlands are strategically placed in the upper portion of the watershed to hold back and slow down water movement. This decreases how fast the water moves to downstream communities, reducing the flood risk. Along with these water quantity benefits, these structures can also improve water quality and create essential wildlife habitat.
Land Retirement (CRP)
This process involves taking unprofitable and highly erodible farm ground out of production. Once out of production the land is planted to a perennial species, usually native prairie. These areas provide wildlife habitat, prevent erosion, and improve soil health leading to less surface run off.
Funding Mechanisms
- Promote federal and state cost-share programs to comprehensively install conservation systems on critical lands throughout the watershed.
- Encourage the use of low-interest loans through the State Revolving Fund to install conservation practices on agricultural land.
- Head over to the NRCS website to see what funding options are available to you!
It takes 500 - 1000 years for nature to build 1" of topsoil in Iowa.
To provide leadership that helps people improve, conserve, and sustain our natural resources while educating them on the importance and practicality of maintaining our environment and quality of life.
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