Linking morphodynamic processes and Silvery Minnow habitat conditions in the Middle Rio Grande- Isleta Reach, New Mexico
Date
2020
Authors
Fogarty, Caitlin, author
Julien, Pierre, advisor
Morrison, Ryan, committee member
Wohl, Ellen, committee member
Journal Title
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Abstract
The Middle Rio Grande, located in central New Mexico, is home to the Rio Grande Silvery Minnow (RGSM), an endangered species of fish. Much of the RGSM's historical range has been lost due to natural and human-caused alterations to the river. For this study, the availability of RGSM habitat is analyzed in the Isleta reach, a segment of the Middle Rio Grande extending approximately 42 miles from Isleta Diversion dam to the confluence of Rio Puerco. To better understand spatial and temporal trends in morphology and channel geometry, the Isleta reach is delineated into six subreaches (I1, I2, I3, I4, I5, and I6). The purpose of this study is to identify connections between hydraulics, geomorphology, and biology to better explain the changing biological conditions in the river. To assess changes in geomorphology along the Isleta reach, the geomorphic conceptual model developed by Massong et al. (2010) was applied to representative cross-sections in each subreach. The model proposes two pathways that changes in the Middle Rio Grande can follow: aggrading (A) or migrating (M). Through inspection of aerial imagery and cross-sectional geometry data, it appears that the Isleta reach is in stage 3 and migrating stages, M4-M8, indicating high sediment transport capacity. River form was further classified using Cluer and Thorne's (2013) stream evolution model. In 2012, all subreaches were in stage 3 (i.e. degradation) of the model. One-dimensional modeling techniques were used to assess habitat availability for the RGSM from 1962 to 2012. Using the Hydrologic Engineering Center's River Analysis System (HEC-RAS), flow distribution slices were used to compute velocity and depth along a cross-section. Hydraulically suitable RGSM habitat for larvae, juvenile, and adult stages is determined using velocity and depth criteria for the fish proposed by Mortensen et al. (2019). The results suggest that habitat availability follows three typical patterns. Earlier years (1962 and 1972) showed "rounded" habitat curves, while later years (1992, 2002, and 2012) showed "step" and "hook" habitat curves. Detailed maps were produced in ArcMap that aid in the visualization of where RGSM habitat is located within the Isleta reach. These maps suggest that subreaches I1 to I3 contain the most habitat for all life stages. However, much of the habitat is disconnected and far away from the main channel, making it inaccessible to the fish. Through an analysis of restoration potential, it was determined that subreaches I2 to I4 may be areas of focus for river management to increase RGSM habitat. Time-integrated habitat metrics, originally developed by Doidge et al. (2020), is a method of interpolating cumulative RGSM habitat for each year between 1992 and 2019. This method requires input of annual habitat curves and daily discharge data. These inputs are used in a summation of simple linear equations that results in habitat metrics for each of the RGSM's life stages. The results show that larval and juvenile habitat metrics are more sensitive to changes in daily discharge than adult habitat metrics. Ecological relationships were inferred based on plots created by Mortensen et al. (2020) that relate habitat metrics, discharge, occurrence probability and lognormal density. Overall, larvae proved to be strong predictors of population dynamics.
Description
Rights Access
Subject
HEC-RAS
Middle Rio Grande
Rio Grande Silvery Minnow
hydraulic modeling
habitat
RAS-mapper