Extended Naturalized Flow and Reservoir Evaporation Input Files for WAMs

Naturalized flow, which is streamflow representing natural hydrology without the influence of human activity, is a key one of the datasets input to the water availability models (WAMs) that are used in the water rights permitting process, regional and statewide water planning, and other water management activities in Texas. The existing naturalized flow input for most WAMs covers the period extending from the 1940s to the 1990s. Given that some river basins in Texas have, in recent years, experienced record low streamflow associated with the 2010-2015 drought event, having updated naturalized flows is essential for developing reliable estimates of water availability from surface water sources.

In 2021, the Texas Commission on Environmental Quality released updated hydrology datasets for the Rio Grande, Red, Neches, and Brazos WAMs. The Texas Water Development Board's (TWDB's) Water Availability Program has extended naturalized flows and reservoir evaporation for nine (see below) of the remaining river basins for which the WAM hydrology has not been officially extended. In addition, due to a change in how reservoir evaporation was adjusted in the official updated Neches WAM, the TWDB is providing an extended hydrology dataset for the Neches that incorporates the TWDB’s quadrangle reservoir evaporation dataset, without adjustment, as used for the official updates to the Rio Grande, Red, and Brazos WAMs. All datasets have been extended through December 2022. These updated naturalized flow and reservoir evaporation data can be used as auxiliary datasets for water planning and research purposes.

The extended datasets were generated using linear regression between historical gauged flow and existing naturalized flow, between upstream and downstream naturalized flow, and between naturalized flow in adjacent watersheds. For more information on the methodology and verification, please read Extension of Naturalized Flow by Linear Regression Method. The extended net reservoir evaporation input files for the same period are also included here. These datasets were compiled by the existing formulations specified in the respective WAM reports and using the TWDB's monthly gridded reservoir precipitation and gross evaporation data published on Water Data for Texas. If you have more questions, please contact Dr. John Zhu or the Surface Water Division.

List of WAM extended/estimated hydrologic input files


The extended WAM input hydrologic data posted here are based on the past known relationship between observed streamflow and naturalized flows, and naturalized flows among adjacent WAM control points by a linear regression method specified in the study paper listed above, and are subject to revision as additional data and/or updates are made available to the TWDB. The dataset may be continuously updated in the future without notice. Neither the State of Texas nor the Texas Water Development Board (TWDB) assumes any legal liability or responsibility for or makes any guarantees or warranties as to the accuracy, completeness, or suitability of the information for any purpose. Please contact TWDB customer service if you have any questions or comments about the dataset.