ILSAM should only be used for watershed areas greater than 10 square miles.

Considerable effort has been spent to maintain consistency in all of the flow estimates. Consistency means that, in addition to maintaining accuracy, the comparative differences in flow values from one location to another are always consistent with basic hydrologic concepts. However, users of these values are always advised to verify the consistency of the flow estimates for their particular application.

The accuracy of the flow estimate is dependent on various factors including the flow frequency, size of the watershed, and geographic region. Estimates of high flow conditions typically have the least percentage error, with a standard error generally around 10 percent. Estimates of low flow conditions typically have low standard error but percentage errors often greater than 30 percent. Percentage errors are generally lower for larger watersheds and higher for smaller watersheds. Reports cited in the references describe details on the accuracy of the flow estimates and the analyses used to generate the flow values.

The Illinois State Water Survey and/or The Illinois Department of Natural Resources shall not be held liable for improper or incorrect use of the data described or information contained on these pages. These data, information and related graphics are not legal documents and are not intended to be used as such.

The Illinois State Water Survey and/or The Illinois Department of Natural Resources gives no warranty, express or implied, as to the accuracy, reliability, utility or completeness of this information. The user of this system assumes all responsibility and risk for the use of this server and the Internet generally. he Illinois State Water Survey and/or The Illinois Department of Natural Resources disclaims all warranties, representations or endorsements, express or implied, with regard to the information accessed from, or via, this server or the Internet, including, but not limited to, all implied warranties of merchantability, fitness for a particular purpose or non-infringement.
 
Official Illinois State Water Survey Data Disclaimer.

Please contact the Illinois State Water Survey with questions regarding the accuracy and appropriate uses of these data or concerning proper data citation.