Storm Water Storage
Jones & Henry has performed large storm water storage studies (for watersheds up to 6,500 acres) which have analyzed the rainfall/runoff characteristics of these watershed basins. In an effort to alleviate downstream flooding, our firm has made various recommendations leading to the designs of retention/detention basins with overflow weirs, underground storage, existing weir structure modifications, and recommendations for the removal of repeatedly flooded structures.
The first approach to any storm sewer storage analysis is to define the design basin. This is accomplished through evaluating the area’s topography, both visually and as provided by the local mapping groups. From the topography a basin boundary can be defined which encompasses the area which will ultimately drain to the discharge point(s) for the basin. The areas that are less dense and have significantly more green space and open areas lessen overall runoff.
Due to ever increasing development, green space is continually being eliminated to allow for new construction projects. These projects can effectively triple the amount of runoff produced during rainfall events. As such it is critical that new developments store a portion of the “post-development” runoff in on-site storage facilities.
There are numerous methods to increase on-site storage; the most obvious being detention basins. Detention basins can be sized to handle a variety of return interval storms (i.e. 1-yr, 5-yr, 25-yr, etc.). Of course land is a valuable asset and must be used wisely. As such unique approaches are called for to maximize on-site detention storage.
Other storage methods include underground storage, typically created through constructing concrete basins or tunnels to augment heavy wet weather flows. Weirs can be installed in existing underground structures (or in above ground storage basins) to effectively add storage, however, this approach must be closely evaluated to avoid localized flooding and dynamic profiling may be required.
Jones & Henry has considerable experience with these types of projects and has assisted clients with the development of:
- Site maps showing topography, drainage areas, discharge structures and outfalls, paved areas and buildings, and storage areas
- Estimates of impervious surfaces and total area drained by each outfall
- Designs of storm water retention basins based upon pre vs. post development conditions
- Stage-storage relationships utilizing computer modeling, SWMM, dynamic profiling, etc
- Water quality analyses related to pollutant concentrations due to scour deposition, dry weather conditions, snowmelt, etc
- Quantitative data based on samples collected during storm events for required parameters