Model Library

Long Term Hydrologic Impact Analysis (L-THIA)

Model name: Long Term Hydrologic Impact Analysis (L-THIA)

Developed by: Purdue University in collaboration with the U.S. Environmental Protection Agency (EPA) (Last update: 2023 (L-THIA GLWMS))

Model type: 1D, process-based, hydrological, watershed model

Computational requirements: L-THIA is currently available in three forms: 1. L-THIA WWW: spreadsheet version requiring Microsoft Excel; 2. L-THIA GIS is a set of Avenue scripts that automate the process of runoff impact modeling within ArcView; 3. L-THIA GIS WWW: requires a custom java interface within a web browser.

Link to download model

Capabilities and Limitations:

Capabilities

  • It focuses on the average impact, rather than an extreme year or storm;
  • Simple model, quick and easy to use;
  • It allows stakeholders to quickly evaluate urban development's impact on runoff and the potential benefits of proposed LID practices.

Limitations

  • L-THIA/LID model assumes that future climate conditions and land use changes will follow historical patterns (Zhu et al., 2023);
  • L-THIA/LID does not account for the potential impact of extreme storms (Zhu et al., 2023);
  • It does not consider some factors such as slope or elevation (Brar, 2019; Zhu et al., 2021);
  • It is not meant to assess the details for requirements of a storm water drainage system and other such urban planning concerns (Purdue University, n.d.);
  • It simplifies the SCS CN method by neglecting the contributions of snowfall to precipitation, excluding the impact of frozen ground on increased stormwater runoff during cold months, and disregarding variations in antecedent moisture conditions (Purdue University, n.d.);
  • It is not recommended for identifying critical source areas in watershed planning when the problem is complex (Nejadhashemi et al., 2011).

Model Inputs and Outputs:

Inputs

Topography data, LULC data, Soil data, Flow data, Water quality data, Measured annual loads.

Outputs

  • Simulation of runoff, and water quality.
  • Non-point source pollution results.

Examples:

References

Zhu, R., Newman, G., & Atoba, K. (2022). Simulating the impact of land use change on contaminant transferal during flood events in Houston, Texas. Landscape Journal, 40(2), 77-79. https://doi.org/10.3368/lj.40.2.79

Zhang, P., Chen, S., Dai, Y., Sekadende, B., & Kimirei, I. A. (2024). Integrated application of SWAT and L-THIA models for nonpoint source pollution assessment in data scarce regions. Water, 16, 800. https://doi.org/10.3390/w16060800

Objectives

The objectives of the study were to apply the L-THIA model to estimate current and future urban runoff and non-point source pollutants in Houston super-neighborhoods, use hotspot analysis to explore the effects of land use changes on runoff and pollutant loads under different socioeconomic conditions, examine how land use patterns are projected to change by 2045, assess how urbanization could increase direct runoff and non-point source pollutants by 2045, and analyze how these effects differ by socioeconomic conditions across neighborhoods in Houston.

This article examined the distribution of nonpoint source TN and TP pollution in the Simiyu River catchment, using the SWAT model to derive EMC values for various land use types.