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Introduction to Impervious L-THIA

Based on more than 30 years of daily precipitation data for the United States, L-THIA estimates changes in runoff and nonpoint source pollution resulting from past or proposed development. In this model of L-THIA, users only need to input:

  • their location (state and county);
  • the type of soil in the area where the land use change is to occur (available online if unknown); and
  • the impervious percentage by land type, and type and size of land use change that will occur (e.g., 100 acres of agricultural land converted to 50 acres high-density residential and 50 acres commercial).

L-THIA will generate estimated runoff volumes and depths, and expected nonpoint source pollution loadings to waterbodies, based on the information provided by the user. Results can be displayed in tables, bar charts, and pie charts.

The Impervious L-THIA version is best suited for urban land use change analysis.

HOW TO USE THE % IMPERVIOUS AREA INPUT