Developers build subdivisions around a model to maximize profit based on the number of lots they can sell at a price points dictated by the real estate market and the demands of buyers. In theory, on a basic level pursuit of this model in will lead to maximization of economic benefits to everyone concerned - the raw land owner that supplies the land, the developer, builders, real estate agents, and home buyers. But as with all theories, real world application leads to what economists may call negative externalities. What does this have to do with flooding or drainage? It is a complicated way of saying that the way land is developed can lead to problems with dealing with the effects of development that are not necessarily any body's moral fault, with an emphasis on the work "moral," and the words "not necessarily."
There are various factors that relate to flooding and drainage issues that individual homeowners may experience. The number of lots in relation to the overall subdivision geographical area defines density, or subdivision land size divided by lot number. The density of a subdivision is directly related to the amount of impervious surfaces generating storm water, such as roofs, driveways, and streets. The topography of the land subdivided to lots as well as the topography of land both above and sometimes below a subdivision are also factors that affect flooding and drainage. A subdivision down hill from a commercial shopping center, offices, or other commercial uses with a high proportion of rooftops and asphalt parking in relation to land area will experience more drainage and flooding issues if the water is directed through the subdivision by the topography. Water flows down hill.
Subdivisions are developed to deal with flooding and storm water issues around a set of rules that began to evolve more than 40 years ago with the implementation of the Clean Water Act of 1972. This law created a system of implementing performance based clean water standards that required a top down, federal approach to regulating water resources in the United States. The Environmental Protection Agency does not take a direct role in subdivision development regulations, but the laws it administers create a system of standards that devolve down to the local level and result in subdivision development standards.
The regulations implemented on a local level have been enacted in a series of phases over the years as the scope of water regulations of water resources has expanded. The policies of clean water have gradually included storm water as a source of contaminants and regulations have been adopted to decrease contaminants. These regulations do not deal directly with flooding issues or flood plains, or the civil relationships and responsibilities that individual land owners owe each other. The policies are adopted to achieve clean storm water, but they result in regulations that developers have to meet by installing storm water systems to manage runoff from the lots and streets they develop. In Georgia the state has assisted in the development of a model Storm Water Management Manual that local governments adopt in one form or another.
Developers under the current system of regulations and ordinances in effect in Georgia metropolitan areas manage storm water runoff by streets, gutters, and storm pipe systems. The system collects storm water and directs it to detention ponds that are intended to slow and absorb storm water to prevent rapid release into streams and to reduce contaminants. Detention ponds often employ biologic filtration in addition to storing storm water over time to allow release.
In implementing the system around the goal of selling as many lots as possible, developers and their engineers are forced to choose spots for the ponds and the pond outlets. The retention usually must be located on the site of the development. This leads to impacts for someone. Detention cannot be easily placed in the middle of stream, the amount of water on a volume basis will always be greater after development than before, and depending on who is under the outlet, someone will notice an impact. If a developer is successful in routing storm water into a stream bed large enough, the people down stream from the development may notice an incremental impact from other development in the water basin. This is often the case and means that if you are homeowner with a flooding problem that seemed to develop over a period of time, it may be difficult to ever pinpoint which developments caused your problems and interfered with your use of your property.
Sometimes though, the source of development and water might be apparent. Many commercial, school, church, and office developments will logically place detention on the down hill side of the lot line at the edge of their properties. Of course, this means that the outlet for the development's storm water will point down hill and away from the development on an adjoining property owner. Or a detention pond within a subdivision, residential or commercial, may take advantage of topographical low points and other features to put a detention pond within a development. In such an instance, owners within the development are down hill from the flow of directed storm water.
To complicate this further, many properties with flooding problems are affected by a common issue that does not involve modern subdivision design. Many of the current regulations for storm water system design have been implemented in the past decade. Developers who developed subdivisions in the 1980s or 1990s in Georgia may not have incorporated dedicated storm water detention at all. Sometimes they simply directed the water into an existing lake using engineering calculations to prove the lake had capacity to store the drainage. Or they may not have planned at all. But again, all water has to go somewhere and a lake that was full before development will be just as full, after a rain, as it was before. To muddy the waters even further, new developments after the adoption of regulations are being retrofitted into existing developments that were built before.
Georgia law places the general obligation to control storm water run off on the up hill property owner who owns property that deviates from the natural condition in a way to cause storm water problems. Finding out where the water is coming from is part of the process of managing a flooding problem that has developed on a piece of property. A land owner may be able to ask or force an uphill owner to reduce or stop storm water flows. If not, then a property owner has to figure out how to direct the water on the affected property to both eliminate his own problem and avoiding causing problems to persons below him.