Ponds and stormwater basins can be great resources to have on a property, and they can provide great benefits for the surrounding area. Regular ponds can be a nice attractive feature for a home landscape and can provide a place for recreation. Stormwater basins act as a water quality feature in areas such as subdivisions by filtering out any pollutants and protecting nearby streams as a result. There are two types of stormwater basins, wet ponds (retention basins, always have water) and dry basins (detention basins, normally bowl-shaped depressions of grass that hold water for a few days after it rains). In this month’s article in the Development Digest, we will dive into a service that we at Warren County SWCD offer to measure the depth of ponds to ensure they have the correct depth needed to function properly. This service is one we offer for all types of ponds; however, we will specifically be looking at newly constructed stormwater retention basins here.
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Having the correct depth is very important when designing a stormwater basin. If a basin is designed incorrectly and is too shallow, it may not provide enough storage for incoming water which defeats the purpose of the basin and may have negative effects downstream. Even with a correctly designed basin, the basin may fill up with sediment during construction, and if that sediment is not removed, this will affect the water depth, and as mentioned above, decrease the storage. During construction, sediment basins need the sediment removed once it reaches ½ of the sediment storage zone and before project completion as well. It is important to measure the depth of the water in a stormwater basin to ensure it is the correct depth and sediment has not filled in the bottom. Here at Warren County SWCD, we can assist with getting an estimate of the depth by providing a free service using a depth finder.

Depth finders are commonly found in the realm of fishing and used by fisherman to get an accurate depth of the water column for fishing purposes. We have found out that we can use a simple depth finder to find the depths of ponds and basins to assess the health of that water feature. We will come out to any pond or stormwater basin per request and use our depth finder to give a good estimate on how deep the pond/basin is. We provide this service because it is important to keep basins healthy and keep the designed capacity to make sure the basin still has its storage and water quality abilities working. Any construction project that is nearing the end and has a stormwater pond should be checked for water depth before being turned over to the next owner. Here at WCSWCD, we would be happy to come out and provide a free depth check using our depth finder.

We also provide this service to HOAs, free of charge, to determine if it is time for the costly dredging project you may be considering. If you are having excessive algae blooms and fish kills in your retention pond, it might be an indicator of a shallow water column. Ohio Department of Natural Resources recommends a pond with a minimum water column depth of 6-8 feet deep to provide a healthy habitat for fish.

It can be costly to dredge a pond of muck that accumulates naturally over time, A rough estimate of when this is needed is 10-20 years after completion or from its last dredging. It can easily cost up to $100,000 or more to completely dredge a large retention pond, so you want to be sure if it is time to do so. We are happy to come out and collect some rough estimates of pond depth and health and we can also provide some contacts for pond maintenance and dredging contractors to point you in the right direction.
 
If you have general pond/basin questions or have questions about our depth finder or want to schedule a site visit with us, please give us a call at (513) 695-1337.
 
Article written by Seth Byerly, Urban/Agricultural Technician
 

​Don’t let stormwater dig a hole you can’t get out of!

​Fast moving water pouring out of a pipe can quicky lead to erosion. Planning ahead and utilizing rock outlet protection can save future maintenance headaches. In this month’s article we will see where this practice is useful, consider design, and review maintenance considerations. Let’s start by identifying where the practice is helpful.
Rock outlet protection can be useful where discharge velocities from a channel, storm drain, or culvert are high enough to cause erosion. The practice can be applied for the following outlet types:

​For design of the rock outlet protection, assume the most severe soil and vegetation cover conditions. The size of the watershed and topography should also be given serious consideration. Rock outlet protection is not intended for slopes greater than 10% or at the top of cut or fill slopes.
Caution should be used if flow rates out of the discharge pipe will exceed 100 cubic feet per second (cfs) for a 10-yr.-fequency storm. Utilize the NRCS Technical Release 55 (TR 55) or other suitable method to determine peak rate of runoff. The outlet protection needs to be stable for the velocity of flow expected from a 10-year frequency storm event. While level spreaders are helpful in conjunction with outlet protections, we will focus on the design of the rock outlet. The width of the outlet should be the width of the headwall or 4 feet wider than the pipe diameter (2 feet on each side of the pipe). The elevation of the downstream end of the outlet protection needs to be equal to the elevation of the receiving stream. The necessary length of the outlet protection and the rock size can be determined from the following figure. 

Larger diameter pipes will require larger rock diameter, a greater thickness for the rock layer, and additional length for the rock channel. The rock riprap needs to be well graded and be placed to obtain a solid and compact layer. Filter or granular bedding is needed beneath all riprap to prevent underlying soil from eroding. Larger size riprap will likely require a thicker bedding layer or 2 different sizes of bedding. Geotextile use can help prevent piping of soil. Care should be taken to properly anchor the geotextile. A properly designed and installed rock outlet protection will help to reduce future maintenance needs.
 
Maintenance will help to protect the riprap, vegetation cover, and associated structural components. The following are key to proper maintenance.

• Determine a responsible party to inspect and maintain the outlet protection.
• Missing riprap should be replaced as soon as possible.
• Protect the outlet from damage by equipment and traffic.
• Fertilize and mow area vegetation to keep a healthy cover.
• Seed and mulch any bare areas that develop.
• Remove sediment and debris.

 
If properly designed, installed, and maintained the rock channel outlet protection should function for decades to come. Lack of proper outlet protection will require more extensive and costly repairs in the long run. Feel free to reach out to our office at (513) 695-1337 if you have any questions regarding rock outlet protection.
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

1. Rainwater and Land Development Manual (Chapter 6.1), 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/6.1_Outlet_Stablization.pdf

Article by Travis Luncan, Urban Technician