Storm Water
One of the major positive impacts of rainwater collection is stormwater management. While you are collecting water than be used for a future purpose, you are also preventing water from running off hard surfaces to cause flooding and erosion. In reducing runoff, water quality in our streams, rivers, and lakes are improved.
As with water supply, the collective impact of rainwater collection on storm water runoff is great. If for example, Metro Atlanta achieves a 100 million gallons per day water supply from rainwater collection, that's a significant amount of water that becomes storm water and potentially runs off.
We can estimate the amount of storm water reduction based on amount of daily rainfall, water usage, catchment area, and size of tank storage. Below we show some estimates that will give you an idea of how much a rainwater collection system can reduce storm water generation. We use our home city of Atlanta as a basis for these estimates. actual results for you will vary case by case depending on your location, your roof size, and your water usage.
The first example we will give is for a simple rain barrel. I this case, let's assume your house has 2,000 square feet of roof and there are 6 downspouts, which is typical. if you are collecting water for the rain barrel from one downspount, again typical, you may be collecting from 333 square feet. If you use water from spring to fall for 8 months and you use it within 7 days after a rainfall, then you will reduce runoff by 10% (90% overflow) of the total that lands on that 500 square feet with 1,000 galloons of water usage. These numbers are worth something but are rather unimplessive.
Looking at a larger rainwater system, the storm water effect becomes more interesting.