Retention ponds were once only used in agriculture and industrial site development, but now they’re commonly found in neighborhoods, and even backyards, in areas with heavy rainfall. Surface level water storage is immensely valuable because it creates space for safely storing large amounts of water that collect on surfaces during a storm. It’s not possible, or feasible, in many areas to build underground sewer systems and drains that could handle the volume of water produced by individual storms. Yet, these retention ponds are often overlooked as just basic drainage ditches or holding cells. Find out why retention ponds are essential to environmental protection and where else they’re used.
The Problem of Runoff
Surface runoff occurs every time rain falls and hits a non-absorbent surface. Soil, especially when covered with vegetation, is good at absorbing water in most cases. When you cover over acres of raw soil with houses, commercial buildings, paved parking lots, roads, and other impermeable materials, you increase runoff. The water traveling over these surfaces picks up contaminants like oil, fuel, pesticides, and silt. It also speeds up and collects in larger quantities, causing erosion when the water travels over exposed soil. Runoff leads to flooding, waterway contamination, stream and river silt accumulation, and many other environmental and property damage issues. Dealing with storm water runoff correctly from the start of a new development is key. Whether the change is as small as a backyard patio or as big as a new highway, runoff must always be a key consideration.
Controlling and Containing Storm Waters
Today’s carefully designed and purpose-built retention ponds arose from natural depressions and waterways that absorbed storm water accidentally. City planners and civil engineers noticed that ditches and drainage basins designed to temporarily retain water could permanently hold it with some minor modifications. The development of modern storm water drainage systems took decades, but today’s fixtures often manage to combine aesthetics, water treatment, and runoff management all into one pond. Connecting these retention ponds and water holding cells with a series of ditches, drains, and outlets can safely recharge nearby wetlands or agricultural areas without causing contamination issues.
Flood and Overflow Planning
Due to their need to deal with unpredictable and changing amounts of rainfall from year to year, it’s easier to design retention ponds to handle flooding rather than to try and completely prevent it. Even building to accommodate 100-year flood levels could leave the pond undersized for a surprising amount of rainfall. Each retention pond or other part of a storm water system should be designed to overflow and drain into a safe area that can handle the surface runoff. Setting aside vacant lots to absorb the overflow of retention ponds has become a common technique used in cities like New Orleans and Seattle. Everything from the size of the drain to the lining for these overflow containment areas need to be considered to prevent flooding damage.
Multiple Levels of Planning and Permits
Since retention ponds are complex projects that can reduce the water availability in one area and increase flood risks in another, they generally need permits at multiple levels of planning. Watershed authorities, natural resource agencies, and even the Environmental Protection Agency (EPA) at the federal level are all commonly involved. Approval usually begins long before construction, so be prepared to adjust the final design before it clears all the permit processes. Improperly designed retention ponds can cause issues like mosquito breeding and odor issues, so there are many vested interests in ensuring the pond is correctly designed. Committing to many aesthetic improvements can also help you qualify for strict permitting requirements aimed at improving water quality and help the feature blend into the landscape.
Why Should Retention Ponds Be Lined?
While the first few generations of retention ponds were usually unlined, this caused quite a few issues. First, retention ponds are generally designed to only lose water through evaporation or drainage. Leaving them unlined allows water to seep out through the soil as well. This can drain water levels lower than desired, leading to quality and odor issues. Seepage also saturates the soil to cause it to become destabilized and suddenly collapse or slide, leading to a collapse of the dam or banks. Retention ponds last longer and are easier to maintain when lined with a durable and flexible material. A geomembrane from BTL Liners is the best choice for most retention ponds, regardless of their size, shape, or total volume.
Retention for Agricultural Purposes
Aside from managing storm water in neighborhoods and urban environments, retention ponds are also widely used in agriculture. They have two main interrelated uses in this field. First, runoff from fields is particularly high in fertilizer, soil particles, pesticides, and herbicides. Building drainage ditches and retention ponds is the best way to keep those contaminants from reaching natural waterways or nearby sensitive soil areas. Second, retention ponds also help accumulate rainwater so it can be used for irrigation later when rainfall isn’t so abundant. Most retention ponds built for farms today combine both features to put the nutrient-rich runoff coming off of fields to good use.
Why Most Retention Ponds Aren’t Decorative
The biggest barrier to building decorative retention ponds is cost. When it’s possible to save money by building a plain and utilitarian design, many developers and local organizations will stick with those simple kinds of ponds. However, spending just a little more on planted and naturalized ponds can do more than just make these water features nicer to look at. Decorative retention ponds also tend to handle nutrient levels better and provide better water processing to improve water quality. They also blend into the landscape more to reduce incidences of trash dumping or unauthorized access. Decorative ponds do require more maintenance to keep them looking good, but they’ll pay back the extra work and costs with continuing performance for years to come.
Make your retention ponds as easy to manage as possible by starting with a reliable and durable liner material. BTL Liners has the reinforced polyethylene (RPE) liners that work well for all retention pond projects. Our liners are also a great choice for the drainage basins, ditches, and storm sewers connecting to the pond. Discuss your plans with our expert team today to get recommendations on which liner to choose.
