Sizing a detention pond is not always as straight forward as it seems, which can lead to costly changes as a project progresses. To ensure that you avoid extending project timelines and unnecessary costs here are the top questions to ask during schematic design.
Questions to ask:
Are there multiple entities overseeing the design? (ex. a DOT and a County) Sizing must ensure you are conforming to both entities requirements which can many times drastically affect a pond’s sizing. Entities often have different requirements and the most restrictive requirements will prevail.
Is the calculation per the c-coefficient for the whole site, is it based on proposed impervious and what does the governing entity consider impervious? Can you receive credit for existing impervious? For more information on claim a credit for existing impervious in the City of Houston, please visit: https://www.houstontx.gov/council/g/Final-Report-Redev-Drainage.pdf
For a plat the governing entity will be reviewing for specific items. Typically:
Proposed easements (though water meter and sidewalk easements are typically recorded via separate instrument.
Building setback lines.
Dedicated forestry setback lines.