Guidance Manua pdf
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- 5.2.3 SRP-CAP Blending
- Feb-01 Apr-01 Jun-01 Aug-01 Oct-01 Dec-01 Feb-02 Apr-02
32 The recommended weekly intensive monitoring program includes the CAP Canal at the Granite Reef Cross-Connect Facility. An observation of elevated MIB levels at this point should trigger an immediate examination of MIB in the CAP system at points R1 (Colorado River), R2A and B (Lake Pleasant), R3 (Wadell Canal), and R4 (CAP Canal at 7 th Street) to determine the source of the MIB and identify an alternative source. For example, if hypolimnetic water had high MIB, releases could be stopped temporarily and deliveries could be made by routing Colorado River water past Lake Pleasant and into the Phoenix area. As a second example, if the Colorado River at R1 had elevated MIB levels during the late fall, deliveries could be halted temporarily and water could be delivered from Lake Pleasant.
In summary, modification of CAP operations has been successful in reducing MIB levels and should be continued.
The concept of blending water sources is simple. For quantities (Q) of two water sources, A and B, the MIB concentration of the blended source (C) is:
[MIB] C = {[MIB]
A
A + [MIB] B *Q B } Equation 5.1 Q A + Q
B
Blending can be used to improve water quality delivered to the Arizona and South Canals, because both canals can receive both CAP and SRP water at the Granite Reef Cross-connect Facility.
For example, if 1000 AF/day was delivered from the SRP system, with an MIB concentration of 10 ng/L and 500 AF/day was delivered from the CAP system, with an MIB concentration of 5 ng/L, the blend in the Arizona Canal would have the following MIB concentration:
MIB = (10)(1000) + (5)(500) = 8 ng/L Equation 5.2 (500 + 1000)
CAP water nearly always has lower MIB levels than SRP water. This is especially true during the late summer and fall, when MIB levels in SRP water are often elevated (Figure 5-3).
33
10 20 30 40 50 60 70 Aug-99 Oct-99 Dec-99 Feb-00 Apr-00 Jun-00 Aug-00 Oct-00 Dec-00 Feb-01 Apr-01 Jun-01 Aug-01 Oct-01 Dec-01 Feb-02 Apr-02 MIB, ng/L CAP SRP
Figure 5-3. MIB in the CAP and SRP inflows to the head of the Arizona Canal.
There is always some blending of CAP and SRP water, which has reduced MIB levels in the Arizona Canal over the past few years. MIB levels at site R13 (about a mile below the CAP inlet) are well-below levels in the SRP water. By deliberately optimizing the blend, MIB levels in the Arizona Canal could be even further reduced. Note that both CAP and SRP waters have relatively low MIB during the early summer, with the exception of March, when the startup of the Salt River moves stagnant water into the Arizona Canal. Later in the summer and into the fall, MIB in CAP water remains low, while MIB in the SRP water increases.
The average monthly differences in MIB concentrations (MIB in SRP water minus MIB in CAP water) is shown in Figure 5-4.
0 5 10 15 20 25 January March May
July September November
Figure 5-4. Average differences in MIB concentrations (ng/L) between SRP water and CAP water, by month, from August 1999 to April 2002. 34 As a general rule, blending to minimize T&O problems in the Arizona Canal would utilize a greater proportion of SRP water early in the season when MIB levels are low in both CAP and SRP waters and more CAP water later in the season, when CAP water has low MIB and SRP water typically has much higher MIB levels.
However, there are a number of institutional issues regarding blending. Some of these include:
1. Water Exchange Agreement. The Water Exchange Agreement was recently modified by the Arizona Legislature to allow water exchanges to occur over periods longer than one year. Water borrowed during one year during an exchange can now be “paid back” at some point beyond the end of that year. This increases the flexibility of SRP-CAP blending.
2. Maintenance of flood capacity. SRP must release enough water from its reservoirs during the later summer and fall to provide capacity for flood protection in the spring. This constraint applies primarily to the Verde River system, which has less storage capacity. The operating goal is to reduce the combined volume of Horseshoe and Bartlett reservoirs to 150,000 AF by the end of October. This constraint is important only in wet years.
3. M&I Agreement. The M&I Agreement between CAWCD and the cities mandates that no city can order more than 11% of its annual CAP delivery in a single month. For Phoenix, with an original allotment of 113,822 AF/yr, this translates to a maximum allotment in a given month of 135 MGD. This constraint may be circumvented during “surplus” years.
4. Capacity of the Arizona Canal. Municipalities share capacity in the “common” part of the CAP Interconnect Canal and in the Arizona and South Canals. The total capacity of the common section is 1,200 cfs. Gates to the South and Arizona Canals each have a capacity of 800 cfs. Phoenix owns 18.75% of the common canal (225 cfs), 31.25% (250 cfs) of the capacity in the turnout to the South Canal, and 60.75% (486 cfs) of the capacity in the turnout to the Arizona Canal. The limiting capacity is the leased capacity from the common portion of the CAP turnout, 225 cfs. During September-October, when T&O problems reach a peak, flows in the Arizona Canal have ranged from about 500 to 800 cfs. Phoenix’s 225 cfs capacity at the CAP turnout would therefore be about one-half to one-third of the typical flow of the Arizona Canal during this period. This limits the extent of blending that can occur with Phoenix acting independently of other cities. A coordinated effort involving other cities, in which each city received CAP deliveries during the peak of the T&O season, would overcome this constraint.
5. Lost revenue. Phoenix is obligated to pay for loss of revenue incurred by SRP if it doesn’t accept its water delivery. This could be a serious constraint up through the time (generally very early October) when SRP switches deliveries from the Salt River to the Verde River.
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