Post-Construction Storm Water controls are very important to every area that has been developed. With development comes an increase in water quantity (more runoff) and pollution to water quality (sediment, oil, etc.). To combat these issues permanent structures must be placed on the site to alleviate the impacts to property owners and ecosystems.
Water quantity is very simple math. Woods, open fields and farms allow much of a rainfall event to be infiltrated into the ground and absorbed by plants for evapotranspiration leaving very little water for runoff. If that land is changed into a subdivision or a mini mall all the roof tops and blacktop parking lots restrict the water from infiltrating or evapotranspirating and instead make more of it into runoff. This can sometimes double or triple the volume of runoff going into our drainage system (ditches, streams, etc.). Imagine a sink and a bucket of water. The running water in the sink is the rainfall, the bucket is the extra volume of water from the rainfall as runoff due to development, the bowl is property owners in that watershed area and the drain is the drainage system. If you run the faucet, water will flow through the drainage system and not flood the property owners. Add the development runoff by quickly pouring in the bucket of water with the rain; the bowl fills up (floods the property owners) in the drainage system because its capacity cannot handle that much runoff. However, this does not mean all development will flood our neighbors. By ponding the increased volume of water and releasing it at a rate equal to the amount prior, we can allow the drainage system not to become overwhelmed. Using the same example, if you were to turn the faucet on and begin to slowly pour in the bucket of water this would not cause the bowl (property owners) to flood.
Sediment is the largest pollutant by volume in the U.S. and is the target for water quality treatment because many of the problems with storm water (pathogens, chemicals, etc.) attach themselves to sediment. Luckily, water quality improvements can be achieved by utilizing some of the same methods for water quantity, sedimentation and filtration. The reason these two items are used is because of their ability to remove sediment without the need for mechanical or a chemical addition. Sedimentation is the process where gravity pulls the sediment particles to the pond bottom before the water is released. Filtration forces the water to flow through a natural media that removes the sediment. The problem with the storm water structures is the long maintenance cycles of these systems. This seems to create a trend of low or no maintenance on the structure itself. Most individuals view the structure like any other part of the lawn. Just like a septic tank whose job is to remove pollutants needs periodic cleaning in a proper manner these storm water structures require the same. Since the structures are designed to capture pollutants the sediment and media removed contains anything from oil to pathogens and should be discarded like septic tank sludge. Educational materials describing the proper maintenance items and intervals of some of these structures are provided on this website.
To maintain compliance under the Trumbull County Phase II Storm Water Program, the Trumbull County Engineers Office has developed and adopted a manual to minimize the impacts from water quantity and quality increases with the Trumbull County Drainage and Erosion and Sediment Control Manual. Any development over 1 acre in this County will not be affected by increased runoff, flooding or pollution because a Storm Water Pollution Prevention Plan is required to be developed and then reviewed by the County Engineers staff.. This effort is just one part of the larger Storm Water Program to reduce water quantity and quality impacts to our waterways in Trumbull County.