Drought Vulnerability of Illinois' Community Surface Water Systems - Vulnerability, Illinois State Water Survey

Drought Vulnerability Classification

Marginal System – Although there is greater than a 90% probability that the current system would have sufficient water during a drought similar to the drought of record, the pending threat of potential shortages during the drought would likely force the community to take extraordinary measures (enacting severe water use restrictions or developing alternative supply sources) to avoid shortages.

Drought Adequacy Description

If a drought similar to the 1952-1956 drought of record were to recur today, it is estimated with 50% confidence that the current system would be able to support a demand of 3.78 mgd (the mid- or best yield estimate). It is estimated with 90% confidence that the current system would be able to support a demand of 2.96 mgd. Although the system would be able to fulfill the community’s current demand of 1.77 mgd with 90% confidence, the drought vulnerability of the system is classified as MARGINAL because the system would not be able to produce more than 1.64 mgd with 90% confidence without using a portable intake in the southern basin of Otter Lake.

Additional Notes