As local land use decisionmakers, municipal and county leaders regularly measure the benefits and costs of development proposals. In addition to factors such as the extension of existing infrastructure and the delivery of government services, local officials are beginning to consider the impact that land use changes will have on a community's water quality.

Land use changes can significantly impact groundwater recharge, stormwater drainage, and water pollution. The Long-Term Hydrologic Impact Assessment (L-THIA) model was developed as an accessible online tool to assess the water quality impacts of land use change. Based on community-specific climate data, L-THIA estimates changes in recharge, runoff, and nonpoint source pollution resulting from past or proposed development. As a quick and easy-to-use approach, L-THIA's results can be used to generate community awareness of potential long-term problems and to support planning aimed at minimizing disturbance of critical areas. L-THIA is an ideal tool to assist in the evaluation of potential effects of land use change and to identify the best location of a particular land use so as to have minimum impact on a community's natural environment.

Differences Between the Models

• Basic L-THIA
  Users only need to input their location, soil type, and the type of land use change taking place.
• Impervious L-THIA
  Allows users to input the percentage of impervious cover of different land uses.
• L-THIA LID
  Allows users to estimate impacts of sustainable development and low-impact practices ( rain barrels, rain gardens, pervious pavers, green roofs, etc.)
• Related Tools
  Other tools from the developers of L-THIA