Fluvial instability and channel degradation of Amite River and its tributaries, southwest Mississippi and southeast Louisiana
Hood, D. Ryan.; Patrick, David M.; Corcoran, Maureen K.
Technical ReportAbstract: The Amite River is a Gulf Coastal Plain stream in southwestern Mississippi and eastern Louisiana. Since the early 1970s, riparian sand and gravel mining has been conducted on a 48-km reach of the river centered on Grangeville, LA. Riparian mining has been considered responsible for instability and changes in the hydraulic and geomorphic regime of the river and local extirpation of the inflated heelsplitter mussel. Field and rotary-wing aerial studies were conducted along the main stem of the river and along the principal tributaries including Beaver Creek, Darling Creek, and the Comite River. These studies indicated that the greatest erosion was occurring along the mined reach; however, erosion was also occurring upstream of the mined reach and along tributaries along and upstream of the mined reach. Erosion was less prevalent downstream of the mined reach; however, erosion was present on the Comite River which enters the Amite River downstream of the mined reach. Bridge survey data for the Amite River showed that the channel width upstream, along and downstream of the mined reach had, respectively, increased by as much as 25, 50 and 60 percent. Historical, rectified panchromatic aerial photography revealed that stream length upstream and downstream of the mined reach, between 1953 and 1998, had decreased, respectively, by as much as 5 and 29 percent. During the same period, the reach downstream of the mined reach had increased by as much as 7 percent. Historical, stream gauge data were examined for six stations along the main stem of the Amite River and four stations on the Comite River. These data for Amite River stations above the mined reach did not reveal a significant trend; however, the data for the one station along the mined reach showed a significant decrease in both peak annual stream flow and peak annual gauge height. Two stations downstream but near the mined reach revealed increases in peak annual streamflow, annual mean streamflow, and peak annual gauge height. The most distal station from the mined reach indicated decreased peak annual streamflow and peak annual gauge height. The Comite River stream gauge data indicated that there have been historic increases in annual mean streamflow and peak annual streamflow; however, peak annual gauge height significantly decreased or remained relatively constant. These data support the notion that the processes acting on the Comite River are distinct and unrelated to riparian mining. The Comite River erosion is considered to be caused by increased runoff and gully development due to land use/land cover changes related to increased urbanization in the Baton Rouge area. The Amite River erosion is attributed entirely to riparian mining. The shortening and straightening of the river is considered to be due to the movement of water into the riparian mines during high-water events. Thus, these high-water discharges tend to cut off or straighten the bends in the river similar to, but on a larger scale than that of natural meander cutoffs.
Geotechnical and Structures Laboratory (U.S.)Engineer Research and Development Center (U.S.)
Amite River; Channel degradation; Comite River; Fluvial geomorphology; Fluvial habits; Gravel mining; Gullying; Imagery; Riparian mining; Streambank erosion; Stream gauge data
ERDC/GSL TR ; 07-26.
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