The Rio Grande/Rio Bravo (hereafter referred to as the Rio Grande) in the Big Bend region of Texas, USA, and Chihuahua, and Coahuila, MX has substantially narrowed since the early 1900s. This narrowing has been exacerbated by the widespread establishment of non-native giant cane (Arundo donax) and tamarisk (Tamarix spp.), both of which help trap sediment and protect banks from natural erosional processes. Substantial declines in tamarisk have occurred with the introduction of the tamarisk leaf beetle (Diorhabda spp.), and by mechanical removal. Recently, large-scale removal of giant cane using fire and aquatic-approved herbicide has occurred. However, the relative impact of vegetation-management actions on channel morphology is unclear. This study aims to address that topic through repeated high-resolution surveys at a variety of study sites within Boquillas Canyon, Big Bend National Park, which has been the geographic focus of much of these removal efforts.
Background & Importance
This project aims to quantify how the removal of dense stands of non-native vegetation effects channel morphology of the Rio Grande. Historical geomorphic analyses showed that processes of channel narrowing and vertical-floodplain accretion was exacerbated by dense stands of non-native vegetation which stabilized the channel banks and helped trap additional sediment thereby affecting the lateral-channel dynamics that was historically an inherent geomorphic process of the river. Removal of these species was conducted in order to restore some of these lateral channel dynamics, increase native riparian biodiversity, and restore overgrown campsites.
General Methods
Channel and floodplain topography is measured annually using terrestrial lidar, total stations, real-time-kinematic GPS, and acoustic Doppler current profilers (ADCP) at a number of study sites within Boquillas Canyon, Big Bend National Park. These data are combined to build high-resolution digital-elevation models. Geomorphic change detection is then conducted to quantify the amount and style of topographic change between successive surveys. Geomorphic changes are then linked to the previous year’s hydrograph, the stage-discharge relations of that hydrograph, as well as the continuous suspended-sediment transport record to determine the dominant magnitude, duration, and seasonality of flows that caused the changes. Vegetation surveys are conducted concurrent with the geomorphic surveys such that the post-removal vegetation response can be correlated with geomorphic change and process.
Topographic data from this project is also being used to help build and calibrate 1- and 2-dimensional hydraulic models such that floodplain inundation of various geomorphic surfaces can be determined, and that flood flows associated with historical flood deposits can be modeled. These data will provide insight into the geomorphic organization of the Rio Grande in Boquillas Canyon, and how flood flows control that organization. Additionally, the combination of offshore topographic data collected using ADCPs and onshore topographic data collected using terrestrial lidar can help inform how topographic changes affect the distribution of aquatic habitats.
- Overview
The Rio Grande/Rio Bravo (hereafter referred to as the Rio Grande) in the Big Bend region of Texas, USA, and Chihuahua, and Coahuila, MX has substantially narrowed since the early 1900s. This narrowing has been exacerbated by the widespread establishment of non-native giant cane (Arundo donax) and tamarisk (Tamarix spp.), both of which help trap sediment and protect banks from natural erosional processes. Substantial declines in tamarisk have occurred with the introduction of the tamarisk leaf beetle (Diorhabda spp.), and by mechanical removal. Recently, large-scale removal of giant cane using fire and aquatic-approved herbicide has occurred. However, the relative impact of vegetation-management actions on channel morphology is unclear. This study aims to address that topic through repeated high-resolution surveys at a variety of study sites within Boquillas Canyon, Big Bend National Park, which has been the geographic focus of much of these removal efforts.
Background & Importance
Healthy giant cane in 2012 on the banks of a river before management treatment. Giant cane response to management treatement in image below. (Credit: Jeffery Bennett, National Park Service. Public domain.) This project aims to quantify how the removal of dense stands of non-native vegetation effects channel morphology of the Rio Grande. Historical geomorphic analyses showed that processes of channel narrowing and vertical-floodplain accretion was exacerbated by dense stands of non-native vegetation which stabilized the channel banks and helped trap additional sediment thereby affecting the lateral-channel dynamics that was historically an inherent geomorphic process of the river. Removal of these species was conducted in order to restore some of these lateral channel dynamics, increase native riparian biodiversity, and restore overgrown campsites.
General Methods
Channel and floodplain topography is measured annually using terrestrial lidar, total stations, real-time-kinematic GPS, and acoustic Doppler current profilers (ADCP) at a number of study sites within Boquillas Canyon, Big Bend National Park. These data are combined to build high-resolution digital-elevation models. Geomorphic change detection is then conducted to quantify the amount and style of topographic change between successive surveys. Geomorphic changes are then linked to the previous year’s hydrograph, the stage-discharge relations of that hydrograph, as well as the continuous suspended-sediment transport record to determine the dominant magnitude, duration, and seasonality of flows that caused the changes. Vegetation surveys are conducted concurrent with the geomorphic surveys such that the post-removal vegetation response can be correlated with geomorphic change and process.
Topographic data from this project is also being used to help build and calibrate 1- and 2-dimensional hydraulic models such that floodplain inundation of various geomorphic surfaces can be determined, and that flood flows associated with historical flood deposits can be modeled. These data will provide insight into the geomorphic organization of the Rio Grande in Boquillas Canyon, and how flood flows control that organization. Additionally, the combination of offshore topographic data collected using ADCPs and onshore topographic data collected using terrestrial lidar can help inform how topographic changes affect the distribution of aquatic habitats.
Dead giant cane in 2014 on river bank (same location as image above) after management treatment. (Credit: Jeffery Bennett, National Park Service. Public domain.) - Publications
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