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Research shows mounting erosion at Montopolis stretch of Colorado River linked to impervious cover, researchers say
Summary
A University of Texas researcher told the commission that increased impervious cover and the Longhorn Dam’s hydrology have produced substantially higher erosion rates at Montopolis than at less developed control sites, and requested updated lidar data to refine planning and mitigation.
Liesl Poppenhaus, a researcher at the University of Texas, presented an analysis of human‑induced sources of erosion on the Lower Colorado River at Montopolis.
Poppenhaus said urbanization and increases in impervious cover have altered the river’s hydrology by delivering larger, faster runoff pulses to the channel, a pattern that accelerates bank erosion and degrades habitat. She explained that Montopolis is particularly susceptible because the Longhorn Dam upstream slows water and allows suspended sediment to settle before release; the resulting clear, high‑energy flows tend to pick up sediment from banks and deepen erosive impacts downstream.
Using comparative measures, Poppenhaus said erosion volumes at Montopolis were ‘‘tens of thousands’’ of cubic meters per year in the study intervals she presented, compared with tens to hundreds of cubic meters per year at a less developed control site. She also documented a growing urban gully system and said a LIDAR resurvey would help the city refine assessments and prioritize intervention.
Commissioners asked for overlay products that could join erosion mapping with planning overlays (for example East Riverside development layers) and Poppenhaus said she could share maps and additional data after the meeting.
Her recommendation emphasized the role of land‑use choices and impervious cover in shaping floodplain stability and urged better coordination of development, stormwater and mitigation planning.
