Archive for September, 2012

How Rainwater Collection Helps Alleviate the Effect of Drought

September 3, 2012

At Ecovie, we are asked often about what to do with rainwater collection during a drought.  The question comes from the thought that you cannot catch rainwater if it not raining.  While that is obviously true in the short term, rainwater collection has a beneficial impact on drought issues both during the drought and when the drought has passed.  Collected rainwater provides much added water supply during droughts when the infrequent down pour occurs.  And, when the drought passes collected rainwater aids in replenishing aquifers so they are available when the next drought arrives.

Let’s take the metro Atlanta area as an example of impact of rainwater collection during a drought.  In 2007, we had the least rain in 50 years with outdoor watering bans and threats of our reservoirs running dry.  During that year, the amount of rainwater that could be captured as about 70% of what can be captured in an average rainfall year. Surprisingly, the 32 inches of rainwater we did receive in 2007 fell at times when we really needed it like in July and August.  Even thought that 32″ was around 18 inches below average, it equals an average year in other parts of the country like the upper Midwest and far exceeds the average rainfall of other areas in the western US.

Collectively, we project that if Atlanta can achieve a 30% adoption rate of rainwater collection over the next 10 years or so, water supply will average 100 MGD of the approximate 650 MGD we current withdraw.  This would deliver around 70 MGD during a drought like 2007 which is certainly enough to help alleviate the impact of drought not only to the metro area, but also to downstream users like farms and communities who would have more downstream flow to use.  This amount would be additive to current supplies due to reduced runoff to the oceans and due to reduced evaporative losses.  As runoff is reduced during the infrequent drought rain storms, it can be put to use and then released for downstream use when it is not raining.  Evaporative loss is a bigger issue with our reservoirs than one may think.  For example, the evaporative loss from Lake Lanier alone averages around 122 MGD.  Rainwater collection eliminates this evaporative loss to actually allow for increased releases downstream.

After the drought passes, rainwater collection aids in our ability to replenish groundwater supplies in our aquifers.  The impact can be seen in the immediate metro area as well as downstream.  If compared to the water supplies from wells which always deplete ground water supply, rainwater collection for irrigation always has the effect of replenishing groundwater.  Compared to new reservoirs and the above mentioned evaporative loss, the added water supply from rainwater collection decreases demand on reservoirs to increase downstream release.  This reduces agricultural demand on wells while helping replenish aquifers.

Somewhat more controversial but based on scientific research, building reservoirs actually can have an impact on weather patterns.  With large open bodies of water instead of the trees that were where the new reservoirs exist, rainfall may tend to pass over the watershed area to fall elsewhere.  This would be a reduction in water supply potential of new reservoirs.

In the ways described above, rainwater collection is one of several sound water management techniques that can minimize the impact of drought.  Along with low impact development using newer storm water management techniques to slow runoff and replenish groundwater supplies, rainwater collection needs to be considered more than it is currently.