WSP07311

• File Number: 8240.300.03
• Description: San Juan River - Recovery Implementation Program - General Info
• Basin: San Juan/Dolores
• Water Division: 7
• Date: 1/1/1998
• Title: Secrion 9 ‎(Preliminary Draft)‎ Conclusions
• Water Supply Pro - Doc Type: Report/Study

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Recommended Hydrograph Conditions

These hydrograph recommendations are designed to meet the conditions required to develop
and maintain required habitat for the endangered fish species and provide the necessary
hydrographic conditions for the various life stages of endangered and other native fish. The
conditions are listed in terms of flow magnitude, duration (days at or above specified magnitude)
and frequency (average recurrence of the conditions specified expressed as a percent and a
maximum allowable duration of years without meeting the condition). In most cases there is a
primary recommendation for a specific frequency of occurrence of a minimum duration for a
specified flow rate. In addition to the primary recommendation, variability in duration is
desirable to mimic a natural hydrograph. Therefore, a frequency table for a range of durations
for each flowrate is recommended. The recommendations are based an statistics for the 1929-
1993 period. Following are the conditions specified:

A.

Category:
Duration:

Flows> 10,000 cfs during runoff period (March I-July 31)
5 days minimum, natural variability maintained by meeting the
conditions in Table 9-1.

Frequency: 20% on average. Minimum frequency for other durations listed in Table
9-1. Maximum period without meeting the specified conditions - 15
years.

Purpose: Flows above 10,000 cfs provide significant out-of-bank flow, generating
new cobble sources, change channel configuration providing for channel
diversity and provide nutrient loading to the system for improved habitat
productivity. Such flows provide material to develop spawning habitat
and maintain channel diversity and habitat complexity necessary for all
life stages of endangered fish.

B.

Category:

Flow> 8,000 cfs during runoff period

Duration: 10 days minimum, natural variability maintained by meeting the
conditions in Table 9-1.

Frequency: 33% on average. Minimum frequency for other durations listed in Table
9-1. Maximum period without meeting the specified conditions - 9 years.

Purpose: Bank full discharge is generally between 7,000 and 8,000 cfs in the San
Juan River below Farmington. Bank full discharge approximately I year
in 3 on average is necessary to maintain channel cross-section. Flows at
this level provide sufficient stream energy to move cobble and build
cobble bars necessary for spawning for Colorado squawfish. Duration of
5 days at this frequency is adequate for channel and spawning bar
maintenance. However, research shows a positive response of abundance
of blue head sucker with increasing duration of flows above 8,000 cfs from
o to 19 days. Therefore, the minimum duration was increased from 5 to
10 days to account for this measured response.