Geology topics

Research about Atchafalaya River basin

Source-linked reports with geographic coverage including Atchafalaya River basin.

4 recordsLinked to original sources

USGS2022

Hydrologic connectivity and residence time affect the sediment trapping efficiency and dissolved oxygen concentrations of the Atchafalaya River Basin

Little is known about water movement, volume, or residence time (RT), and how those characteristics affect sediment trapping efficiency (TE) and dissolved oxygen concentrations (DO) in the United States' largest remaining bottomland hardwood swamp, the Atchafalaya River Basin. To better understand these dynamics, this study used bathymetry, lidar, and stage records to determine volumes in the Basin's hydrologically distinct water management units (WMUs). Discharge measurements determined flow distribution and RT. Residence time was compared with DO to identify conditions that coincided with DO increases or decreases. Suspended sediment concentrations (SSC) were used to determine TE relative to calculated and measured discharge and RT. Discharge through units (85–2,200 m 3 /s) and RT (0.37–231 d) depended on connectivity and river stage. At high stages, with water temperatures >20°C, DO in the largest WMU declined by −0.21 mg/l/day. DO trends indicated less well-connected areas of the WMU contributed hypoxic waters as the flood wave lengthened and stages fell. In the two WMUs examined for TE, TE (−266% to 99% and up to 38 Gg/day) correlated with hydrologic connectivity, SSC, RT, water volume, and, in one WMU, discharge losses. Long RT and high TE indicated a high potential to process nutrients. These relationships varied among WMUs. Large volumes of sediment-laden water moving over the floodplain combined with long RT, high TE, and hypoxia indicate that this ecosystem has continental-scale importance in reducing nutrient loads to the northern Gulf of Mexico. Reports from other systems suggest similar processes may be operating on other large river floodplains globally.

Louisiana↗

USGS2022

Hydrologic modification and channel evolution degrades connectivity on the Atchafalaya River floodplain

The Atchafalaya River Basin is the largest remaining forested wetland in the contiguous United States. Since 1960, dredging and channel erosion in the Basin have resulted in changes to the hydrologic connectivity that have not been quantified. Analyses were conducted to determine the hydraulic and geomorphic factors that have changed since discharge became controlled that may have decreased river/floodplain connectivity. We examined: (1) stage/discharge relationships from 1960 to 2014; (2) hydroperiods across the floodplain; (3) discharge distribution to the floodplain by comparing discharge measurements from 1959–1968 to 2005–2012; and (4) channel cross-sections and floodplain elevations. Our results indicate that much of the floodplain no longer receives headwater discharge (upstream to downstream, > 200 km 2 ) or receives too little discharge to alleviate stagnancy and hypoxia in the forested wetland at lower stages. Large portions of the Basin (400 km 2 ) have low water levels controlled by channel geomorphology and sea-level rise that inundate the forested floodplain for more than 50% of the calendar year. This extended duration of inundation contributes to hypoxia and likely reduces nutrient retention. The confinement of discharge to a large efficient channel compromises the ability of this system to respond to sea-level rise and subsidence. This study provides insight to the effects of flood management projects along Coastal Plain rivers and deltas.

Louisiana↗

USGS1998

Resource management of forested wetlands: Hurricane impact and recovery mapped by combining Landsat TM and NOAA AVHRR data

A temporal suite of NOAA Advanced Very High Resolution Radiometer (AVHRR) images, transformed into a vegetation biomass indicator, was combined with a single-date classification of Landsat Thematic Mapper (TM) to map the association between forest type and hurricane effects. Hurricane effects to the forested wetland included an abrupt decrease and subsequent increase in biomass. The decrease was associated with hurricane impact and the increase with an abnormal bloom in vegetation in the impacted areas. Impact severity was estimated by differencing the biomass maps before and immediately (3 days) after the hurricane. Recovery magnitude was estimated by differencing the biomass maps from immediately (3 days) after and shortly (1.5 months) after the hurricane. Regions of dominantly hardwoods suffering high to moderate impacts and of dominantly cypress-tupelos suffering low impacts identified in this study corroborated findings of earlier studies. Conversely, areas not reported in previous studies as affected were identified, and these areas showed a reverse relationship, i.e., highly impacted cypresstupelo and low or moderately impacted hardwoods. Additionally, generated proportions of hardwood, cypress-tupelo, and open (mixed) forests per each 1-km pixel (impact and recovery maps) suggest that regions containing higher percentages of cypress-tupelos were more likely to have sustained higher impacts. Visual examination of the impact map revealed a spatial covariation between increased impact magnitudes and river corridors dominated by open forest. This spatial association was corroborated by examining changes in the percentage of open forest per 1-km impact pixel; the percentage of open forest peaked at moderate to high impacts. The distribution of recovery supported the impact spatial distribution; however, the magnitudes of the two indicators of hurricane effects were not always spatially dependent. Converse to univariate statistics describing a11 forested area within the basin, higher recoveries tended to be related to higher percentages of hardwoods. Lower recoveries, on the other hand, tended to be related to forests with nearly equal percentages of hardwoods and cypress-tupelo.

Louisiana↗

USGS1976

Simulation of forest changes related to hydrologic variables in the Atchafalaya River basin, Louisiana

Results of forest-trend modeling from one data set in the Atchafalaya River basin show that predicted forest acreage totals for 16 forest types agree within 30 percent of actual values in two-thirds of the comparisons. A forest-trend simulation model based on statistical regression relations of forest and hydrologic variables and constrained by forest succession concepts was developed using observed data from twenty-four 8-square-mile (20.74-square-kilometre) quadrats. Forest and hydrologic data at each quadrat were sampled in time at three 4-mile (6.44-kilometre)-wide strips across the basin. The model predicts changes in forest-type acreages due to hydrologic change in time steps, or forest acreage transition, of 21 years. Further basin-wide quadrat simulations are planned using hydrologic input data from a flow-sediment model of the basin currently being developed. Other ecosystem models could be appended to the forest-trend simulation model.

Louisiana↗