Assessment of Suspended Sand Availability under Different Flow Conditions of the Lowermost Mississippi River at Tarbert Landing during 1973–2013

Abstract

Rapid land loss in the Mississippi River Delta Plain has led to intensive efforts by state and federal agencies for finding solutions in coastal land restoration in the past decade. One of the proposed solutions includes diversion of the Mississippi River water into drowning wetland areas. Although a few recent studies have investigated flow-sediment relationships in the Lowermost Mississippi River (LmMR, defined as the 500 km reach from the Old River Control Structure to the river's Gulf outlet), it is unclear how individual sediment fractions behave under varying flow conditions of the river. The information can be especially pertinent because the quantity of coarse sands plays a critical role for the Mississippi-Atchafalaya River deltaic development. In this study, we utilized long-term (1973-2013) records on discharge and sediments at Tarbert Landing of the LmMR to assess sand behavior and availability under different river flow regimes, and extreme sand transport events and their recurrence. We found an average annual sand load (SL) of 27.2 megatonnes (MT) during 1973 and 2013, varying largely from 3.37 to 52.30 MT. For the entire 41-year study period, a total of approximately 1115 MT sand were discharged at Tarbert Landing, half of which occurred during the peak 20% flow events. A combination of intermediate, high and peak flow stages (i.e., river discharge was ě18,000 cubic meter per second) produced about 71% of the total annual SL within approximately 120 days of a year. Based on the long-term sediment assessment, we predict that the LmMR has a high likelihood to transport 4 to 446 thousand tonnes of sand every day over the next 40 years, during which annual sand loads could reach a maximum of 51.68 MT. Currently, no effective plan is in place to utilize this considerably high sand quantity and we suggest that river engineering and sediment management in the LmMR consider practices of hydrograph-based approach for maximally capturing riverine sediments.

Estimating bed material fluxes upstream and downstream of a controlled large bifurcation ‐ the Mississippi‐Atchafalaya River diversion

“…Days at the low flow stage accounted for about 50% of the time, but they only transported ~20% of the total BML. Joshi and Xu (2015) studied suspended sand availability under different flow regimes using 41‐year suspended sand (SS) data measured at Tarbert Landing (Figure 1). They also found that intermediate flow transported the most SS (i.e., 21% flow for 34% SS load) and peak flow was the most effective range to deliver SS (i.e., 3% flow for 13% SS load).…”

“…Located about 10 km downstream of the ORCS, Tarbert Landing gauging station operated by the USACE has long‐term suspended sediment concentration data. Utilizing these data, Rosen and Xu (2014) quantified total suspended sediment and Joshi and Xu (2015) estimated suspended sand load for the past four decades at Tarbert Landing. Knox and Latrubesse (2016) estimated bedload transport using a time‐lapsed bathymetric method immediately downstream of Tarbert Landing.…”

Sediment Trapping by Emerged Channel Bars in the Lowermost Mississippi River during a Major Flood

“…Assuming a bulk density of 1.2 metric tons per cubic meter (i.e., a typical bulk density for silt-pure soil), the total volume of trapped sediment during the 2011 flood would be about 1.0 million metric tons. Joshi and Xu [43] analyzed the long-term relationship between discharge and sand load for Tarbert Landing and developed a daily discharge (q) and daily sand load (S) rating curve as below: From their study on a three-year sediment budget (2008-2010), Allison et al [16] reported an average loss of 67 MT/year total suspended sediment in the river reach from TBL to St. Francisville at river kilometer 419, and 80% of the sediment loss was sand, i.e., about 54 MT/year sand. They attributed the large loss to a deposition in the channel bed and overbank storage.…”

Effects of the human activities on the water level process of the Poyang Lake

“…The enhancement of climate changes and human activities leads to the underlying surface change of the big river, altering basin runoff process [1]. It is surely that the evolution of the relationship between Yangtze River and Poyang Lake accelerated after the Three Gorges Reservoir (TGR) and other controlling reservoirs in the main stream and tributaries, which have been put into operation.…”