Rainwater rolls off the landscape as a trickle, stream, or river. For a light rain event the drainage channel may not matter that much. For a moderate or heavy rain events the design and condition of the drainage channel becomes more critical. A grass swale is one of the stormwater conveyance methods identified in Ohio EPA’s Rainwater Land Development Manual. In this article we will look at good design, stabilization and maintenance of grass lined swales. Many drainage assistance calls we go on involve a swale. Common issues we receive calls on are erosion in the swale, overflow of the swale, and modification/blocking of the swale. Most of these issues are preventable with proper design, building, maintenance of the swale and education of residents/HOA’s.

Design starts with looking at runoff. The area drained, soil types, land use, topography and historic rainfall data all play a role in determining the swale size and how it is stabilized. A swale should be designed to carry the peak rate of runoff from a 10-year flood before it overtops.  If the swale is designated as a Flood Route, it must be designed to handle a 100-year rain event. While it would be well beyond the scope of this article to go through all of the calculations, NRCS Technical Release 55 (TR 55) is one suitable method to determine peak rate or runoff. Grassed swales designed to protect residences and businesses need to have out of bank capacity to carry the peak rate of runoff before water can flow inside adjacent residences or businesses.

Shapes of drainage swales can be parabolic or trapezoidal. The parabolic channel closely approximates natural flow conditions, but design and construction are more complex. Trapezoidal channels are preferred where there will be a large quantity of water or high flow rates. Side slopes that are 3:1 or flatter are recommended.

Next to consider is the channel’s stabilization and resistance to erosion:
Clay soils, which are common in Warren County, offer moderate protection from erosion but good protection once vegetation is established. Sod or seed and matting are preferred to establish vegetation. The grassed swale should be vegetated as soon as possible after reaching final grade. Waiting makes it more difficult to get good stabilization. Delays in stabilizing the slopes will also cause maintenance issues that will later need fixed. Stabilize upslope areas to prevent sediment from washing down and filling in the swale.

Check dams may be incorporated to decrease water flowrate, to reduce erosion, and to allow grass to establish. The rock check dam should be lower in the center so that water does not flow around and erode the edges of the swale. Check dams are often temporary measures. It is good to plan to determine when the check dam will be removed.

For sites with prolonged flows, a high-water table or seepage problems; a subsurface drain or rock-lined waterway may be incorporated. Grassed swales should also have a stable outlet with adequate capacity to prevent ponding or flooding damage.

Beyond design and construction of the swale, owners should consider ongoing maintenance. Most important would be to ensure that residents don’t block, modify or build in the swale. Grass growth should be monitored to insure a vigorous stand of grass. Protect the swale from compaction or damage due to equipment or traffic. Fix damaged areas immediately. With good design maintenance and stabilization, a swale will protect property and prevent future maintenance needs.
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References:

1. Urban Hydrology for Small Watersheds (TR-55), United States Department of Agriculture Natural Resources Conservation Service. June 1986. Web link for this publication is available at:

https://nationalstormwater.com/wp-content/uploads/2020/07/Urban-Hydrology-for-Small-Watersheds-TR-55.pdf
   2. Rainwater and Land Development Manual (Chapter 6.7), Ohio Environmental Protection Agency. May 2025. Web link for this publication is available at: https://dam.assets.ohio.gov/image/upload/epa.ohio.gov/Portals/35/storm/technical_assistance/6.7_Open_Channels.pdf

Stormwater Infrastructure helps to convey rainwater, prevent flooding of homes, roadways, all while protecting water quality. Many factors can impact water quality. In this article we will look at water temperature and how stormwater infrastructure can help maintain healthy streams and lakes.
As areas become more developed there is an increase in impervious surface area. On a sunny day paved surfaces can transfer heat to the air above them and to stormwater as it flows over. The surface temperature of a parking lot can exceed 140°F on a clear summer day. This is almost hot enough to fry an egg. During a rainstorm, pavement also allows water to flow unimpeded into the storm drains. Water flowing off hot pavement becomes warmer and can cause thermal stress to organisms living in the receiving stream.

Fish and macroinvertebrates, tiny organisms which make up the base of the aquatic food chain, have a temperature range that they are well adapted to. Think of trout living in a cool mountain stream. Fish have adapted over many thousands of years to the environments in which they live. Increasing the temperature of a stream over time or subjecting the stream to sudden fluctuations in temperature will stress the fish populations in that stream. Some heat tolerant species will survive while less tolerant species will see a drop in numbers. There are many reasons for this, one of which is dissolved oxygen. Colder water can hold more oxygen which fish breath through their gills. Warmer water holds less oxygen. While our native fish populations do worse with increased stream temperatures, certain algae species can do well in warmer waters. These algae will bloom, creating additional stress on the fish since they can deplete oxygen in the water. To further complicate things, urbanization typically results in less tree canopy around streams resulting in less shade and higher water temperatures.

​Stormwater controls can help to reduce thermal stress on fish and other aquatic organisms. Grassed swales can slow down water and help it to infiltrate. Establishing clearing limits around streams helps to maintain a filter buffer or better yet, a tree canopy around the streams.
How can stormwater infrastructure help to maintain good water quality. One piece of infrastructure that can make a big difference is the basin.

In our example of hot water flowing off a parking lot, the basin slows the flow down giving the water time to cool to safer levels. Once in the basin heat transfer can occur between the water and the basin. Some transfer also takes place between the water and the air. The rate of heat loss is determined by the “specific heat” of water. The specific heat it is the amount of energy needed to change the temperature of water by 1 degree. A significant amount of energy needs removed to reduce the temperature of water. We can’t change the air temperature or how much rainfall is received.  What can be influenced is how long it takes water to flow through the basin. This is done by oversizing the basin and by installing the water quality orifice when converting the outlet structure over to post construction design. A larger basin will have more storage, increasing the water quality storage volume. The orifice plate or restriction plate is made of stainless steel and restricts the volume of water that can leave the basin in a given time. The person installing the plate should consult the Storm Water Pollution Prevention Plan (SWPPP) for which size orifice plate to install. Properly designed and maintained stormwater infrastructure helps make our rivers and streams a little cooler.

For more information, contact our office at 513.695.1337

The Industrial revolution saw a large amount of pollution being dumped into America’s waterways, and treatment plants were either non-existent or a far-cry compared to what they are today. The Cuyahoga River in Cleveland, Ohio was so polluted with toxic sludge that it caught fire, multiple times! The environmental revolution of the 1960s and 70s led to many environmental regulations, as people saw how poorly we were treating our environment and ecosystems. In 1948, the Federal Water Pollution Control Act became the first U.S. law to combat water pollution. This was amended in 1972 to become The Clean Water Act (CWA). The CWA has helped make the nation’s waters safer and cleaner, allowing communities to return to the water for swimming, fishing, and recreation. Environmental laws like the Clean Water Act aren’t going away. They are still needed to continue protecting America’s cherished natural resources for future generations.
The Clean Water Act established the National Pollutant Discharge Elimination System (NPDES). There are a multitude of pollutants that enter America’s waterways, so there are a multitude of permits regulating discharge to those waterways. The NPDES permit we will focus on today, is the Construction Stormwater General Permit (CSGP). This permit allows discharge of stormwater from construction sites, provided that certain treatment practices are installed during construction.

Why is Dirt so Dirty?
Sediment is the largest pollutant in Ohio’s lakes and streams, so the CSGP aims to reduce the amount of sediment-laden water being discharged from construction sites. Excessive sediment in waterways can cause fish kills and disrupt ecosystems. It clouds the water column and makes it hard for aquatic life to breathe and find food. Fertilizers, pesticides, herbicides, and other pollutants also bond with sediment. It turns out that Ma was right all along. Dirt is dirty. So, take your shoes off at the door!

When is the Permit Required?
We are currently in the sixth generation of the CSGP. This Ohio EPA permit (OHC000006) is required for any project that will disturb one or more acres of earth. It is required to discharge stormwater from the construction site when the ground is exposed to the elements and erosion occurs. More information regarding this permit can be found here.
To obtain coverage, the applicant must submit a Notice of Intent (NOI) to the Ohio EPA. Once this permit is received from the EPA, a Stormwater Pollution Prevention Plan and Earth Disturbing Permit (EDP) Application must be submitted to our office for review to ensure sediment and erosion control measures will be installed throughout the project. The EDP application can be found and submitted here. Our urban technicians inspect the site each month to make sure the permit requirements like sediment and erosion control measures are being upheld. When the project is complete and the site is stabilized, a Notice of Termination (NOT) must be filed to close out the permit coverage. These applications can be found in the Ohio EPA eBusiness Center Surface Water Tracking, Reporting, and Electronic Application Management System (STREAMS) here.

Who Is Responsible for Sediment and Erosion Controls?
The contact listed on the CSGP Notice of Intent (NOI) application or the designated SWPPP contact is responsible for upholding permit requirements and maintaining sediment and erosion control measures throughout the duration of the project. Sometimes it’s a building company that does the total site development and the construction. In other cases, there may be a developer who only does the grading, roads, and utilities, but then a builder comes in for the construction later. In this case, the permit coverage needs to be transferred to the builder(s). If there are multiple builders, each builder would need to sign up as a co-permittee to the overall site permit. That way, each builder is aware of their responsibility for individual lot controls to keep sediment contained.
In a situation where each house is a separate builder, and disturbance is less than one acre, the permit is still needed. Ohio EPA refers to this type of project as a Common Plan of Development (as defined in Appendix A of the CGP). This occurs when there is a contiguous area where multiple separate and distinct construction activities may be taking place at different times on different schedules under one common plan. There are two ways permit coverage can be transferred, Co-Permittee coverage and Individual lot coverage.
 
Co-Permittee Coverage
Co-permittees can be added to a permit if there are multiple developers or contractors working on a project that falls under one general permit and there are centralized sediment and erosion controls (controls that address runoff from one or more lots, I.e., a basin or ditches/inlets along roadways not associated with a specific developed lot). A common example of this is a large residential subdivision development with centralized storm control features that has different builders working on different sections/lots throughout the development. Without obtaining the co-permittee coverage for those different contractors, the original overall development permittee (typically developer/SWPPP contact) retains the responsibility of both the centralized sediment and erosion control measures and the individual lot controls. Therefore, adding those entities as co-permittees to the project transfers responsibility of individual lot controls maintenance to the builders/contractors and the developer retains responsibility of the centralized features.

Individual Lot Coverage
If there are no centralized storm control features and the transfer of permit coverage will not prevent or impair the implementation of controls, the original permittee can transfer responsibility to individual lot owners. In this case, the original permittee must temporarily stabilize sold lots, inform the new lot owner of his permit obligations, and ensure that an Individual Lot NOI application is submitted to the Ohio EPA at least seven (7) days prior to the date the new lot owner intends to accept permit responsibility.
 
In both the case of adding co-permittees and obtaining individual lot permit coverage, the lot owner should obtain a copy of the original SWPPP and comply with its requirements. Depending on site topography and location, additional controls above and beyond those outlined for the "typical" lot may be required. The new lot owner may also be partially or completely responsible for amending the SWPPP and installing those controls.

For more information please contact Warren SWCD at 513.695.1337

Fast moving water can cause a LOT of damage! Many problems can arise from water flowing at a high velocity. This is especially the case when talking about a high flow rate in concentrated areas such as ditches or swales. Erosion is an issue that can result from the high velocities that may occur in ditches or swales, and so it is important to find ways to mitigate the erosion in the best way possible. Check dams are a great option that can be installed in ditches and swales to decrease the water velocity and in some cases keep sediment from washing downstream.

​Check dams are constructed structures built up as a wall in a flow path that serves the purpose of slowing down water velocity. Many check dams consist of 4–8-inch stone and are no higher than 3 feet tall and are constructed along the width of the swale/ditch. Check dams can also be constructed of material such as compost filter sock. As mentioned above, check dams can also serve the purpose of keeping sediment from washing downstream. However, not all types of check dams are good for sediment control. Rock check dams are an effective way to slow down velocity and prevent erosion, however, rock is not an effective method to keep sediment from washing away due to the pore space in the material that sediment can wash right through. Filter socks are designed to keep sediment from washing downstream, and so if the goal is to slow the velocity of the water AND keep sediment in, then a filter sock check dam might be the best option.  

Maintenance Considerations:

• Per the Rainwater and Land Development manual, once sediment has built up to one-half the original height of the check dam, the sediment should be removed.
• Removal of the check dam should occur once earth disturbance has ended and the upland area has been stabilized. Once the check dam has been removed, the area should be graded and seeded to match the surrounding area per the design.
• Routine inspections are also a great way to ensure the check dam is working effectively.

 
For more information on the design criteria and specifications about check dams, please visit the OEPA Rainwater and Land Development Manual chapter 5.1. For regulations regarding construction and earth disturbance in Ohio please see the OEPA NPDES Construction General Permit.