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This response is somewhat oversimplified, but...
I cannot state strongly enough that, almost without exception (probably 99.99%+ of the situations), the closer you manage stormwater to the location at which precipitation reaches a surface, the better stormwater management you will achieve - locally and regionally. This can be accomplished in an extremely low-cost and sustainable manner, actually reducing the cost of many (or most) real estate development projects relative designs which focus on conveyance.
Such is fundamental to mimicking the predevelopment watershed response from a site. Also, retention - as opposed to detention - is needed to mimic the predevelopment watershed response and should be the primary focus. Detention should be used only when retention is not feasible. Measures that includes retention as feasible are also lower cost than systems that don't include retention. Detention basins that *sustain* an elevated postdevelopment runoff flow rate (relative to predevelopment) can be worse than no detention at all relative to stream erosion and downstream flooding depending upon runoff flow timing.
Full stormwater management would address the following:
1. Quantity: Postdevelopment total quantity (mass, volume) of stormwater infiltrating the soil surface at the site, evapotranspirating from the site, and flowing from the site by way of surface runoff (eg, open channel flow, sheet flow, pipe flow) should mimic the predevelopment total quantity (mass, volume) of stormwater infiltrating the soil surface at the site, evapotranspirating from the site, and flowing from the site by way of surface runoff (eg, open channel flow, sheet flow, pipe flow).
2. Character: Postdevelopment character (instantaneous flow rates, site hydrograph shape) of stormwater runoff from the site should mimic the predevelopment character (instantaneous flow rates, site hydrograph shape) of stormwater runoff from the site.
3. Constituents: Postdevelopment instantaneous, event, and total mass of constituents transported from the site by surface flow (stormwater runoff) and subsurface flow (soil water) should mimic the predevelopment instantaneous, event, and total mass of constituents transported from the site by surface flow (stormwater runoff) and subsurface flow (soil water).
I suggest the following documents and W3 sites as a start in investigating this matter.
Design: Low Impact Development Manual
(
Interim Code of Practice for SUDS
Low Impact Development Technical Manual
(
Sustainable Urban Drainage Systems Network
The Practice of Low Impact Development
Water Sensitive Urban Design
Water Sensitive Urban Design Guidelines for the City of Knox
Low Impact Development (LID), Water Sensitive Urban Design (WSUD), Green Coving (GC), Minimal Impact Development (MID), Sustainable Urban Design Systems (SUDS), and various other terms are generally slight variations on the same theme: "buzz" words/phrases for marketing a stormwater management approach intended to be sustainable.
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tsgrue: site engineering, stormwater
management, landscape design, ecosystem
rehabilitation, mathematical simulation
