Hydraulic Habitat Suitability for the Rio Grande Silvery Minnow at the Los Chavez Irrigation Outfall, New Mexico

Date: 2023/08/01

Author(s): Ormsbee, H.A.

Publication: University of New Mexico Thesis



It is essential to manage the Middle Rio Grande for aquatic species to preserve the native biodiversity of the river. During periods of low flow, endangered species such as the Rio Grande Silvery Minnow (RGSM) may get trapped in a drying reach without the ability to escape from isolated pools. Very little is known about how areas of refuge, such as irrigational outfall channels, buffer RGSM from stream flow intermittency. Hence, there is a crucial need to quantify available habitat for RGSM in areas of refuge. This study aims to make connections between flow regimes and physical-habitat conditions to help inform the operation of the Los Chavez outfall, specifically for the benefit of the RGSM. Two-dimensional hydraulic simulations were performed to characterize inundated areas and areas of suitable hydraulics for a range of discharges. Eco-value curves were created to delineate a discharge/habitat relationship for larval and adult life stages. Results from this study indicate that available areas increased for larval and adult RGSM as more water was released from the outfall, however there was a diminishing return in available habitat with outfall flows above 15 cfs. The Rio Grande did not contribute to floodplain habitat until flows reached 1000 cfs. The outfall itself provided little suitable v habitat for larval RGSM, but the channel provided suitable habitat for adult RGSM once the outfall converged with the sandbar. Larval RGSM had suitable habitat in the floodplain at each Rio Grande and Los Chavez discharge. Adult RGSM had suitable areas in the outfall and surrounding floodplain at each Rio Grande and Los Chavez discharge.