222 Delta Evolution from Rivers to the Shelf: Past, Present and Future Perspectives for Society (Posters)
The session focuses on deltas and adjacent depositional environments from fluvial systems to the continental shelf. Research on modern, ancient or extraterrestrial deltas that emphasize their importance to our society is welcome.
Tuesday, 21 October 2025
8:00 AM - 5:30 PM
HBGCC, Hall 1
Damming and Water Use Increase Flood Risk in the Lower Rio Grande
Paper number: 222-0
Program: Technical Sessions
Time: 8:00 AM – 8:00 AM
Authors
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Tian DongThe University of Texas Rio Grande Valley, Edinburg, TX
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David DeanUnited States Geological Survey, Flagstaff, AZ
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Joel SankeyUnited States Geological Survey, Flagstaff, AZ
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Timothy GoudgeThe University of Texas at Austin, Austin, TX
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Ana RodriguezThe University of Texas Rio Grande Valley, Edinburg, TX
Abstract
The Lower Rio Grande (LRG) stretches 460 km from Falcon Dam at the upstream (0 km) to the Gulf of Mexico, forming part of the US-Mexico border and supplying water to approximately 2.8 million people binationally. Irrigation mainly began during Spanish colonization and intensified after the 1920s, remaining the dominant water use today. The closures of Falcon Dam (1954), Anzalduas Dam (1960), and associated irrigation infrastructure have substantially reduced both flow and sediment supply, driving significant changes in channel geometry. However, the impact of these changes on river sustainability, particularly flood risk, remains unstudied. Thus, this study analyzes channel changes in the LRG to assess associated flood risks using lidar topography, aerial imagery, and hydrologic records. Since the closure of Falcon Dam, peak and mean discharges have declined from 2,473 and 192 m³/s to 565 and 95 m³/s in the upstream segment (Falcon to Anzalduas, 0–175 km), and from 702 and 127 m³/s to 145 and 22 m³/s in the downstream segment (Anzalduas to Gulf, 175–460 km). The more severe reductions downstream are primarily due to water use. Consequently, channel narrowing and incision are ubiquitous, especially downstream, where the average channel width decreased from 124 m in 1912 to 47 m in 2011. A narrow inset floodplain has developed approximately 2.9 m below the 1912 bank elevation, and the bankfull cross-sectional area shrank from 528 m² to 213 m². Although incision has lowered the channel bed, narrowing has offset this effect by reducing the flood-carrying capacity. For flows over 100 m³/s, modern river stages downstream can rise up to 2 m higher than pre-dam conditions for equivalent discharges. Overall, upstream damming, compounded by water extraction, has drastically changed the Lower Rio Grande channel and, as a result, increased flood risks.
Geological Society of America Abstracts with Programs. Vol. 57, No. 6
doi: 10.1130/abs/2025AM-413590
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