After Hurricane Harvey, special consideration to stormwater detention basins are top of mind with any new project. With as flat as Harris County is, it’s paramount that there are places to store potentially damaging floodwaters temporarily until the channels can safely carry the water away.
Depending on the size of the site and the governing entity, planning the space for detention can be challenging.
For example, if you outfall into a County roadway (as opposed to a Harris County Flood Control District ditch/ basin), you need to meet County criteria. They will not allow you to flood your immediate neighbors trying to get flows to the regional detention basin; a conveyance path must be included in the design. This is becoming a significant challenge for smaller commercial lots within a MUD (Municipal Utility District) that are trying to tie into a MUD pond within proximity of the property.
To narrow the design and cover all bases, make sure that you know the answers to the following questions:
Where is this site allowed to outfall? A detention pond always has an outlet. Once water reaches a certain level, it needs a place to go.
Is regional detention an option? This could be very beneficial if cost of land is high and utilizing all available area is of higher importance.
Once you determine whether or not there are multiple options for outfall, then determine which entity provides what the project necessitates. If the timeline is tight, coordinating outfall to a DOT can be undesirable as review time is usually more extensive than other entities. If that is the only option for outfall it’s imperative that plans get to them for review as soon as possible.
If only one option for outfall is available, how deep is the ultimate outfall and what is the allowable flow rate?
Based on either allowable flow rate per an existing drainage area map, or if it’s based on impervious cover increase, how big does your pond/pipes/underground storage need to be and can it feasibly fit on the site and provide the developer what they require to receive their return on investment?
Have questions regarding detention and your next project? Feel free to reach out to us at PRD Land Development. We’re here to help, and are committed to being the go-to solution on projects that are too complicated for the average civil engineering firm.