IFRs below Friant Dam

[alanccai]

Following a phone call with an operator/ restoration flow manager at Friant Dam, this is my proposed method for determining IFRs below Friant Dam:

Alan’s recommended approach: (1) Use our projection method to forecast umimpaired runoff at Millerton Reservoir for the entire Water Year [note that they arrive at this by adding together computed unimpaired runoff to Millerton Reservoir through the present day, and, the projected runoff for the remainder of the Water Year] (2) Place that number in the appropriate line segment in the “SJRRP Restoration Allocation at Friant Dam as a function of unimpaired runoff at Millerton Reservoir” graph below (Figure 1) (3) For horizontal line segments, no interpolation is required and the appropriate environmental flow release schedule for the specific WYT can be applied immediately. (4) For sloped line segments, an interpolation is needed. The unimpaired runoff number calculated in Step 1 falls somewhere on the sloped line segment. You have the X value (unimpaired runoff), so calculate the Y value. (5) Divide this Y value by the corresponding value in the parallelograms on the right end of Figure 3. These represent the Total Friant Dam Releases at the MIDPOINT of each sloped line segment (also they’re the horizontal dashed line at the middle of each sloped segment in Figure 1). This is the ratio that will be applied in step 6. (6) Find the flow release schedule for the specific water “restoration year type”, and MULTIPLY all the values in that schedule by the ratio calculated in Step 5. (7) This customized flow release schedule is valid until the next time a forecast is made.

FYI: There are two columns of numbers in the “Table 3: Restoration Allocation and Year Type” (Figure 2). In order to achieve the “Restoration Allocation (TAF)”, they estimate that more than that needs to be released from below Friant Dam - “Total Friant Dam Release (TAF)”. Because, some of the water is lost between the release point and the point where the restoration allocations are measured at, the bottom of “Reach 1”, known as Gravelly Point. Losses include riparian diversions. So we should rely on the “Total Friant dam Release” schedule as our IFRs even though not all of it ends up being environmental water.

Known simplifications caused by this method: (1) Ignores ability of restoration flows manager to adjust the timing of flow releases based on on-the-ground conditions (2) Ignores physical constraints that limit the amount of flows released (ex. channel capacity constraints)   Worked out example of this methodology: (1) Suppose my “runoff at Millerton Reservoir for the entire Water Year” is calculated to be 1,600 TAF. (2) This number falls on the light blue sloped line segment in Figure 1 – which corresponds to Normal-Wet WYT. (3) This is a sloped line segment so I can’t just apply one of the csv files of flow release, need to do interpolation (4) The Y value for X = 1,600 TAF is calculated using basic algebra is 421.31 TAF. This is the specific SJRRP Annual Allocation at Friant Dam. (5) The ratio of 421.31 to the y value at the dashed line in this line segment, 473.851 TAF (473.851 is also found in the parallelogram on the right side of Figure 3) is 0.88911915348. (6) Multiply all the values in the flow release schedule for Normal-Wet years by 0.88911915348. (See “IFR_Below Friant Dam_cfs_daily.csv” in https://github.com/vicelab/sierra-pywr/files/3856720/IFR_Below.Friant.Dam.zip). This becomes the custom flow release schedule, until the next time an updated runoff forecast is made.

Figure 1

Figure 2

Figure 3

Source for images: http://www.restoresjr.net/?wpfb_dl=2044 Which are a more user friendly version of the tables found in Exhibit B (page 54) of http://www.restoresjr.net/download/settlement-related/Settlement_Stip_Final_As_Lodged_091306.pdf

[alanccai]

The relevant csv files are here: IFR_Below Friant Dam.zip