Stormwater Is More Than Wastewater
Flooding is the first thing that many associate with the words storm water. In reality storm water runoff should be seen as a wasted resource and a lost opportunity. Storm water is groundwater and stream base flow that we allowed to escape through poor or misguided attempts to "control" storm water.
Before the surface of the land is developed, the precipitation that falls in the form of rain or snow percolates through the soil and is stored beneath the surface of the land. That water collects in cracks in the bedrock and void spaces between particles of subsurface soil, sand and unconsolidated rock. This zone of water saturated material is called an aquifer and is the source of the water we pump from wells and the source of the water that feeds our streams through springs and seeps.
When we begin to convert the land from forests and meadows to housing subdivisions, commercial areas and industrial parks the opportunity for precipitation to infiltrate into the ground is disrupted. Impervious surfaces like rooftops, parking lots and roads prevent rain and melting snow from seeping back into the ground. The problem is further compounded when we collect the runoff, concentrate the flow and pipe it to the nearest stream. The result is a reduction in available groundwater, reduced stream flow in dry periods, water pollution and increased flooding.
Every drop of rainfall or snowmelt that is conveyed to a stream by our storm water systems is a lost resource. It reduces the amount of water stored in the aquifers and results in wells that become unreliable or dry up altogether, and streams that once flowed year round, dry up in the summer or during periods of drought.
Normal stream flow, known as base flow, is not supplied directly by storm water runoff. Storm water floods the streams during rainfall and shortly thereafter. The water that flows in the stream within a few days after a storm is that water which is stored in the aquifers and reaches the surface through springs and seeps. There is a direct relationship, when more precipitation ends up as storm water runoff, the streams suffer a reduction in base flow and often dry up altogether.
Storm water runoff is also a major source of surface water pollution. The pollutants that are picked up and carried by storm water runoff include trash, pet waste, pesticides and fertilizer from lawns, parks, golf courses and farm fields. Oil, grease, heavy metals and other materials deposited on streets and parking lots are also flushed into streams by runoff. Soil and sediment carried by the rushing water smothers stream bottoms and the creatures that live in the stream. This is known as non-point source pollution and it accounts for a major portion of the pollutants that enter our surface waters. Individuals who dump waste oil, antifreeze, grass clippings, other unwanted materials and pet waste into storm water inlets, basins, and streams or directly onto the ground or paved surfaces compound the problem.
Flooding is the most obvious indication of our failed policies for dealing with storm water runoff. Spending huge amounts of money to build structures designed to prevent flooding is not cost effective and has not worked. Effective storm water management does not begin at the end of a pipe it begins at the source and deals with precipitation where it falls. Building a storm water management system around the concept of detention and peak rate of flow control has also not worked and actually contributes to downstream flooding.
At first glance it appears reasonable to control storm water by collecting it and holding it behind a dam or in a detention basin for a period of time after which it is released at a controlled rate. Unfortunately, this approach ignores one very important factor. More total volume of storm water runoff is being created because these solutions do not address storm water creation at the source. As a result, more water over time is discharged to our streams to cause flooding rather than being infiltrated into the ground and made available for storage in our underground aquifers.
The solution to dealing with storm water is simple, return the precipitation that falls to the ground where it can replenish the underground aquifers, support plant and animal life (including humans!) and provide base flow for streams and waterways. The practical means for accomplishing this goal are not terribly difficult if one remembers the most important principal, deal with storm water at its source.
Starting at our own homes, where does the water that falls onto the roof go? Is it immediately piped into the nearest storm drain or paved surface, or is it made available for later use by saving and collecting it? One of the simplest solutions any homeowner can use is a rain barrel which collects water directly from the rain gutter downspout and stores it for watering plants or gardens. More elaborate solutions include constructing drywells which are underground rock filled pits which store and slowly release runoff into the ground. Infiltration trenches utilize the same technique in a linear fashion.
The construction of new housing offers the greatest opportunity to build infiltration into the design from the beginning. Minimum disturbance construction practices involve the clearing and stripping of vegetation and topsoil only from those areas absolutely necessary for construction of roads, parking lots and buildings. By limiting disturbance, the natural ability to infiltrate is not disrupted or destroyed. Natural areas such as forests and meadows left intact can be utilized to help infiltrate runoff from impervious surfaces.
Standard roadway, parking lot and driveway construction results in almost 100% runoff of precipitation. This does not need to be the case. Simply eliminating the standard curbing in residential areas, allows runoff to seep into the ground rather than collecting it and conveying it to the nearest storm drain. Porous paving systems for parking lots and driveways allow precipitation to percolate through the pavement and into storage/infiltration beds constructed beneath. Runoff from rooftops and walkways can also be directed into the beds. Not only does this technique restore lost infiltration opportunities, it eliminates the need to construct storm inlets and piping systems to carry the runoff away. Best of all, it eliminates the need to construct detention basins that waste valuable land and don't infiltrate runoff and recharge groundwater.
While some runoff is unavoidable, the method chosen for transport can also affect the amount that either is infiltrated or lost as storm water to a stream. Vegetated swales, infiltration trenches, perforated piping and conversion of existing detention basins to infiltration basins can all reduce the amount of runoff that is transported to streams. Anything that lengthens the path that storm water runoff takes helps to increase the amount of water that is infiltrated and reduces flooding impacts downstream.
Reduced non-point source pollution is also one of the benefits of storm water infiltration. Instead of pollutants being washed directly into streams by runoff, infiltration allows those pollutants to be filtered out by vegetation. Soil microbes breakdown and make nutrients available for plant life on land, not algae growth in streams, lakes and ponds.
Development that recognizes the value of the natural landscape in controlling runoff, protecting groundwater resources and maintaining stream flow is called conservation design. When done properly, development does not have to cause flooding, deplete groundwater and dry up streams. Conservation design can also lower infrastructure costs because it incorporates natural features into an overall plan that minimizes the cost of building new man made systems to replace the natural systems that are destroyed by traditional development design.
Over the past several years, Buckingham Township has taken steps to change our subdivision and land development ordinances so that stormwater facilities are designed to maintain the natural hydrologic conditions that existed before development. It is our goal to reduce or eliminate stormwater runoff at its source, prevent pollutants from entering our waterways and underground aquifers and protect the natural flow in our streams. We welcome the participation and assistance of all Buckingham residents in protecting our water resources.