Does Rainwater Harvesting Help Reduce Runoff Pollution? The answer is yes. All these pollutants are carried by the stormwater runoff. By reducing stormwater runoff, these pollutants can be prevented from entering a body of water. Runoff can be reduced by harvesting rainwater. The more rainwater is collected, the greater the amount of pollutants removed from a body of water.
The table below shows the amount of pollutants that can be removed depending on the amount water contained.
The concentrations of each pollutant can be obtained from the environmental data. These concentrations were multiplied by the storage capacity (gallons) to obtain the amount of pollutant removed (kilograms). The table reflects the total quantities from all five watersheds. Some pollutants are neglected in this analysis because their concentrations are too small.
This relation can also be represented graphically. The following graph represents total suspended solids removed vs gallons of rainwater stored. All pollutants will behave the same.
Permeable pavement and rain gardens are highly used to help reduce runoff pollution. However, any other method of rainwater harvesting can serve this purpose as well.
Can Rainwater Harvesting Alleviate Flooding? It is complicated to come up with an answer since many factors are involved. For simplicity, we can assume the following:
Neighborhood size: 800 houses-270 acres
Heavy rainfall: 9.9 inches -"Tax Day Flood" rainfall average in one day
Rooftop size: 1800 square feet
Rainwater harvesting method used: A regular system for each house with tank size of 2,100 gallons
The following table shows the amount of water that fell in the entire neighborhood:
Although this is the total amount of gallons that fell over the area, it is not the total amount of water that becomes runoff. Some water becomes trapped in depression, some evaporates, and some of it infiltrates into the soil. For this reason, to come up with better estimations of runoff, the average rainfall needs to be corrected and the potential gallons must be recalculated.
This shows an estimation of the volume of the runoff.
Now, with the assumption stated above, the maximum harvesting potential for the neighborhood based on the rooftop size can be calculated.
In this case, just like the scenario stated in the Cost-Benefit Analysis, there would be a surplus of water, since each house would need to have a tank size of 9,492 gallons. For our assumptions, each house only has a 2,100 gallon tank, which means the entire neighborhood can only collect 1,680,000 gallons. Now, converting this to inches of rain with the values stated above, only 0.23 inches of rain would be retained, which is insignificant.
Data and formulas to obtain estimations are based on the environmental study. [42] Other data was based on the assumptions above and the rainwater harvesting system petitioner manual. [36]