Google Maps Interface for Online Watershed Delineation.

LTHIA Low Impact Development Spreadsheet.

What is LTHIA:

Community planners, developers and citizens of a community should be aware of the long-term impacts of landuse change on their environmental resources. LTHIA, Long-Term Hydrologic Impact Assessment, is designed to help these people to quantify the impact of land use change on the quantity and quality of their water. This tool uses the land use and a soil characteristic from the user along with thirty years of precipitation data to determine the average impact that a particular land use change or set of changes will have on both the annual runoff and the average amount of several non-point source pollutants. For those unfamiliar with the hydrologic (water related) impacts of land use change this tool along with the supporting documents will hopefully give the user enough information to start asking questions about land use changes in their area.

[ How LTHIA works ]

Spreadsheet and OWL LTHIA

There are several input screens for Standard L-THIA (using TR-55 curve numbers), which are available below.

For residents of EPA Region 5 states, there is an online GIS version which automatically categorizes landuse and soil based on your location. [ Online watershed delineation (OWL) and LTHIA ]

For those new to L-THIA and land use planning Basic Screening is a good place to start. There are eight choices for land use types which most land uses fall into. For those familiar with land use planning terms or need to describe a custom land use, Lot Level Screening gives more land use and BMP options. The choices for land uses includes 6 lot sizes for residential housing and an option to employ detailed LID BMPs.

Fact Sheet for LTHIA in Swan Creek

Powerpoint(tm) for LTHIA workshop in Swan Creek

Fact Sheet for LID-LTHIA

Powerpoint(tm) for LID-LTHIA workshop in Swan Creek

Tutorial for hands-on training at Swan Creek workshop.