Technical Report

Examining Alternative Water Management Strategies to Support Rio Grande Silvery Minnow Conservation Within and Across Years

URL: https://webapps.usgs.gov/mrgescp/documents/Walsworth-and-Budy_2022_Alternative-Water-Management-Strategies-to-Support-RGSM-Conservation.pdf

Date: 2022/01/17

Author(s): Walsworth T.E., Budy P.

Publication: Prepared for U.S. Bureau of Reclamation, 17 p.

Abstract:

Major Takeaways

• Single year management simulations
  • Incorporating both shifts in flow timing and additions of discretionary water outperforms strategies incorporating only one of these methods.
  • When limited amounts of discretionary water are available and there is a low capacity to shift flows across time, strategies focusing on supplementing summer or both spring and summer flows perform best.
  • As the amount of discretionary water available and capacity for shifting flows across time increases to very high levels, strategies focusing on supplementing spring high flows perform better than those focusing on summer low flows.
  • Choice of management strategy matters most in low water years.
• Multi-year management strategy simulations
  • The ability to store water in high flow years for use in later low and medium water years is a highly effective strategy relative to those strategies focusing only on in-season management.
  • Fifteen of the 20 top-performing strategies incorporated supplementing summer flows in low water years as at least part of their approach.
  • Performance of strategies supplementing flows only during spring high flow periods is highly sensitive to the volume of discretionary water available.
• Impact of summer drying intensity
  • During low water years, the probability of meeting RGSM population targets declines rapidly between 500 and 1200 mile-days dry.
  • Reducing either the extent or duration of drying within this region can greatly increase the probability of achieving annual population goals.
• Impact of adding discretionary water to the spring high flow period
  • Adding discretionary water to spring high flow periods had a limited impact until nearly 35,000 – 40,000 AF of water was added in years with low or moderate summer drying intensities.
  • In years with high summer drying intensities, even larger volumes of discretionary water were required to register a meaningful increase in the probability of meeting density targets.