Memorandum: November 8 2009 Agenda Item 11 Water Supply Protection Section

• Description: Memorandum: November 8 2009 Agenda Item 11 Water Supply Protection Section
• State: CO
• Date: 11/8/2009
• Author: Kowalski, Ted; Bassi, Linda
• Title: Memorandum: November 8 2009 Agenda Item 11 Water Supply Protection Section
• Water Supply Pro - Doc Type: Board Memo

Wet Typical
119 (108) 68
79 (57) 19
5 (0) 0
25% Years
Dry Typical
127 (106) 68
33 (14) 0
0 (0) 0
25% Years
Driest
87 (73) 53
25 (1) 0
0 (0) 0
25% Years
The numeric criteria shown in the above chart are based on simulated future stream flow
conditions based on past natural stream flows coupled with future demands and system
operations (herein "simulated future flows ") instead of existing hydrology which some
stakeholders (including those representing the boating recreation community) maintain is
not protective of the ORVs. The entire Stakeholder Group agrees to implement
cooperative measures when practicable (considering available resources and protection of
the other ORVs) in order to maximize the number of Usable Days for each boating
experience category, within each year type. It is anticipated that stakeholders will bring
their specific preferences and goals to the cooperative measure planning process and to
the negotiation of final boating flow guides. The use of simulated future flows as part of
these Provisional Flow Guides does not reflect agreement on the part of the Stakeholders
regarding whether simulated future flows or historical stream flows should be used to
develop permanent Recreational Floatboating Flow Guides, even if [the Poison Pill] was
not exercised.
NOTES:
1. Definitions required for the four year types.
2. A frequency of compliance standard is required for permanent flow guides, or
anything past the 3 -year period.
3. Channel Maintenance Flows are needed for significant sediment transport and riparian
health. As part of the provisional fishing guides and based upon the relevant literature,
adequate channel maintenance flows are typified by overbank flows associated with
less frequent but higher flows, on the order of a 10 year recurrence interval streamflow
of approximately 6,700 -8,000 cfs in the upper W &S reaches.
a. 6,700 cfs is the reported 10 year event from the Grand County Flood
Insurance Study (F.I.S.) published by F.E.M.A (6,700 cfs; 1962 -2006
hydrology); analysis of gaged streamflow data at the Kremmling indicates a
range of 7,000 to 8,000 cfs (1982 -2008 hydrology).
b. Duration of channel maintenance flows should be determined.
c. In the provisional period, appropriate stream segments for further field -based
evaluation of channel maintenance flows should be identified (for all W &S
stream segments). Additionally, a corresponding monitoring protocol should
be developed.
4. Flushing Flows are needed to clean spawning gravels. For the provisional fishing
guides, flushing flows should be 1,800 cfs for 3 -days in duration with a 1 in 2 year
frequency, coinciding with peak flow (based upon Grand County studies).
a. Flushing flow criteria need to be developed for Segment 7.
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