Hydrologic Budget for a Wetland System

Report No: 99-R9

Published in 1998

About the report:

An important functional indicator of the success of a constructed wetland as a replacement for a natural system is the hydrology of a site and whether it is adequate to support wetland vegetation and habitats. For constructed wetlands with potentially limiting hydrologic conditions, such as sites that rely on stormwater runoff as the primary source of water, particular attention to water loss through evapotranspiration (ET) is necessary in determining the water balance. The literature reveals a variety of techniques used to calculate ET and demonstrates the difficulty in estimating ET. Of the methods presented in this report, three empirical relationships were applied to the water balance of a stormwater-supported mitigated wetland. The results were compared to those given by direct measurement. Empirical estimation of wetland ET revealed that the Penman method most closely reflected actual wetland ET, the Thornthwaite method predicted water loss at a rate significantly less than the actual rate, and restrictions of the Class A pan evaporation method rendered the method inappropriate for the given conditions. The accuracy of any empirical estimator to reflect actual ET rates may improve from on-site data collection of climate parameters.

Disclaimer Statement:The contents of this report reflect the views of the author(s), who is responsible for the facts and the accuracy of the data presented herein. The contents do not necessarily reflect the official views or policies of the Virginia Department of Transportation, the Commonwealth Transportation Board, or the Federal Highway Administration. This report does not constitute a standard, specification, or regulation. Any inclusion of manufacturer names, trade names, or trademarks is for identification purposes only and is not to be considered an endorsement.


Other Authors

Shaw L. Yu, Elizabeth A. Fassman

Last updated: December 12, 2023

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