Question: Is there any way to figure out how much water can be absorbed by different ground covers?

stevie is asking a question about stormwater
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by stevie | December 20, 2016 18:00 | #13799

Background story

I'm interested in exploring stormwater, and wondering if I can model different ground covers on an area to figure out how much water would be absorbed were we to use different plants or materials on our property.


Hi Stevie,

The plants you choose probably won't make much difference in water storage during storms because they can't absorb water fast enough. The soil and mulch can absorb water quickly, but unless there is a very deep layer of dry soil and mulch, a rain storm can saturate it in minutes.

I don't know what type of environment you are working in, but I can't think of an environment where the plants themselves can make much difference reducing storm runoff. Dry soil material (if stabilized by plant roots so it does not wash away) can absorb some water and slow runoff at the start of rain events, but after it gets saturated overland flow will quickly carry away all the subsequent rain.

I also don't know what your goal is. If your goal is to retain as much rainwater as possible, a holding basin might be required. If you just want to soak up the rain from small rain events, building up organic material and loose soil will help. Any plants that grow well can stabilize the soil material and intercept the raindrops to provide some erosion protection.


Hi Chris! Sorry I didn't get a notification you wrote in here, so just seeing this now (off to GitHub to report a bug next!). @liz mentioned the Rational Equation helpful link to figure this out here, but I feel like all those factors you are mentioning are really interesting and important and not necessarily taken into account on that method.

One of reasons I'm interested is because we have a number of proposed stormwater projects happening here in New Orleans, and while we're thinking about methods to measure water depth, I was wondering how people estimate runoff/absorption before they start these type of projects.

Yes, civil engineers have empirically tested many different ground covers for how much stormwater they absorb, and from this created "runoff coefficients" for use in an equation (the so-called "Rational Equation") for how much ground is covered by what type of ground cover or paving.

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