Technical Report

Evaluating Middle Rio Grande Flow Alteration at a River Network Scale to Enhance Water Management Opportunities

URL: https://webapps.usgs.gov/mrgescp/documents/Wesche-et-al_2005_Evaluating-MRG-flow-alteration-at-a-river-network-scale-to-enhance-water-management-opportunities.pdf

Date: 2005/08/01

Author(s): Wesche T.A., Wesche L.B., Gensler D., Grogan S.

Publication: Report prepared for Middle Rio Grande Endangered Species Collaborative Program, 59 p.

Abstract:

Our objective has been to investigate stream flow alteration within the middle Rio Grande (MRG) using the Indicators of Hydrologic Alteration (IHA) approach to quantitatively evaluate the degree to which the flow regime has changed over time in response to major 20 century water th development actions. We first identified fourteen U. S. Geological Survey stream flow gaging stations distributed from the Colorado-New Mexico border downstream to Elephant Butte Reservoir with sufficient period-of-record for analysis. Six of these gage stations were located along the mainstem within the designated critical habitat for the Rio Grande silvery minnow (RGSM, Hybognathus amarus). Based upon development history, we divided the available record into three time periods: 1) pre-MRGCD, 2) pre-Cochiti Dam, and 3) post-Cochiti Dam, with at least 20 years of record in each period to mitigate possible discrepancies due to climatic variability. We then applied the IHA method to compare 33 different hydrologic parameters between gage stations and time periods. Four stations had sufficient record to allow comparison of the pre-MRGCD and post-Cochiti Dam periods, while at 10 stations we were able to compare pre-Cochiti and post-Cochiti Dam periods. Four secondary stations, either with shorter periods of-record or located on tributary streams, were also analyzed.

When we compared the pre-MRGCD with the post-Cochiti Dam period, we found overall hydrologic alteration (HA) was low to moderate and quite consistent between stations, with highest HA at the Lobatos, CO gage. At the San Marcial station within the critical habitat, overall alteration was low, with only two of 33 parameters highly altered, the 1-day maximum flow and the flow rise rate. The stream flow target ranges we present for these highly altered parameters could provide guidance for future water management. Also, we found the median date of the annual maximum flow occurred 30 days earlier during the post-Cochiti Dam period, raising concerns regarding the effects of cooler water temperatures on RGSM reproduction.