Effects of Land-Use Change (1938–2018) on Surface Runoff and Flooding
in the Amite River Basin, Louisiana, USA Using Coupled 1D/2D
HEC-RAS–HEC-HMS Hydrological Modeling
Abstract
Formed by Mississippi River sediments, south Louisiana is a flat,
low-lying coastal region with high-clay content soils and heavy annual
precipitation that is particularly susceptible to damage caused by
extreme storms and flooding. In August 2016, a stationary storm system
caused over 50 cm of rain to fall across much of southeast Louisiana.
Largely rural, the major trends in the hard-hit Amite River Basin have
been conversion of agricultural land to forest beginning in the mid-20th
century and rapid urbanization and development spurred by economic and
population growth in the Baton Rouge area following the oil boom of the
1970s, as well as later waves of migration following Hurricane Katrina
and the 2016 floods. This analysis examines the effects of spatially and
temporally changing land use on runoff and flooding within the watershed
and is part of a larger research project which seeks to also quantify
the relative impacts of changes in precipitation and planform geometry.
To quantify the effects of land-use change on flooding, runoff curve
number (CN) maps were created using NRCS soil type data and USGS land
cover data. Areas with a higher CN experience less interception and
infiltration of surface water and the flood risk is consequently
greater. While CN for the Basin overall dropped from 86 to 79 between
1938 and 2018, CN dropped from 82 to 70 in rural areas due to
reforestation and increased from 86 to 90 in the southern portion of the
Basin due to urbanization. These data were then input into the HEC-HMS
and coupled 1D/2D HEC-RAS components of a numerical model of the Amite
River Basin. Flooding behavior under different design storms and land
cover conditions was then observed and quantified. In examining the
major contributing factors to flooding in south Louisiana, this research
project aims to create a more comprehensive understanding of flooding
and propose potential mitigation strategies and design interventions for
alleviating the worst effects.