Alteration of the flow distribution at a river bifurcation caused by a system of upstream dams: Case of the Grijalva River basin, Mexico

Abstract

Multiple factors control the flow distribution in a river bifurcation. However, one factor that requires further analysis is the effect of upstream reservoirs. Such is the case of the bifurcation of the Mezcalapa River into the Samaria and Carrizal Rivers located in the lowlands of the Grijalva River basin, Mexico. Four dams were commissioned in the upper basin, the first in 1967 and the last in 1987. Since the late 1960s the distribution of the flow at the bifurcation has varied considerably. The flow captured by the Carrizal River between the late 1960s and mid 1980s gradually decreased from 40% to 10%, and later, between the mid 1980s and early 2000s, it increased up to 75%. During the same period, the Samaria River had a reversed pattern. Here, using a two-dimensional hydro-morphodynamical model, the impact of an upstream reservoir (that causes homogenization of the flow hydrograph and sediment retention) on bed morphology and flow distribution in a river bifurcation is analyzed. The results indicate that the sediment retention is the factor of largest impact on the flow distribution. The upstream channel incises, and the process propagates to the diffluent with the larger energy gradient developing positive feedback were the erosion increases the hydraulic capacity to capture more flow, resulting in more erosion. The flow homogenization has also an impact. The suppression of peak flows reduces the sediment load capacity in the diffluent with lower energy gradient, generating sedimentation at its entrance and diminishing its hydraulic capacity.

Semicentennial Response of a Bifurcation Region in an Engineered River to Peak Flows and Human Interventions

“…Planform, geometry, sediment characteristics, hydrograph, and interventions vary among them. For example, sediment retention and homogenization of the hydrograph due to upstream dams influence the flow partitioning at the Mezcalapa river bifurcation (Mendoza et al., 2021), the Farakka Barrage in the Ganga‐Padma system affects the flow partitioning at the bifurcation upstream of Hooghly river (Gupta et al., 2014), and the Old River Control Structure determines the flow partitioning at the Mississippi‐Atchafalaya bifurcation (Edmonds, 2012). Long‐term observations of flow partitioning and bed level dynamics will be required to understand how these different bifurcations respond to peak flows and climate change.…”

“…River bifurcations are present in almost every medium-size and large river around the world with different levels of engineering: the Mezcalapa-Samaria-Carrizal system in Mexico (Mendoza et al, 2019(Mendoza et al, , 2021, Ganga-Padma-Hooghly system in India (Gupta et al, 2014), the Bala-Lower Old Danube system in Romania (Yossef et al, 2016), and the Mississippi-Atchafalaya system in the USA (Edmonds, 2012). Planform, geometry, sediment characteristics, hydrograph, and interventions vary among them.…”

Analysis of autogenic bifurcation processes resulting in river avulsion

“…Using a similar approach, Iwantoro et al (2022) studied the effect of tides on the stability of bifurcations by properly varying the downstream boundary conditions. Other evolutionary models of bifurcations available in the literature were tailored to specific case studies, such as bifurcations located downstream a reservoir (Mendoza et al, 2022) and longitudinal training walls in presence of alternate bars in the upstream channel (Le et al, 2018).…”