Technical Memorandum To: Peter Kavounas From: Garrett Rapp, Mark Wildermuth Date: September 18, 2017 Subject: Estimation of Evaporation Losses in Recharge Facilities in the Chino Basin Background and Objective The Chino Basin Watermaster (Watermaster), Chino Basin Water Conservation District (CBWCD), and Inland Empire Utilities Agency (IEUA) operate recharge facilities in the Chino Basin for storm, recycled, and imported waters (hereafter, recycled and imported waters are collectively referred to as supplemental water). Figure 1 shows the locations of these recharge facilities and the types of water recharged. Table 1 lists IEUA estimates of the annual recharge of storm and supplemental water at these facilities for the period of July 2011 through June 2016. These recharge estimates were made assuming that evaporative losses were negligible. Watermaster is interested in determining the magnitude and significance of evaporative losses for storm and supplemental water diverted into the recharge facilities for recharge into the Chino Basin. If Watermaster were to determine that evaporative losses are significant, it would like to establish a method to estimate and apply evaporative losses to storm and supplemental water deliveries to more accurately estimate recharge. Specifically, Watermaster staff is interested in determining if a “postage stamp” evaporation loss rate could be developed that would enable it to assess evaporation losses on all water delivered to recharge facilities. Watermaster directed WEI to: identify sources of data that could be used to estimate evaporative losses from water stored in recharge facilities in the Chino Basin, develop a methodology to estimate evaporation losses at the recharge facilities, and conduct a proof of concept of the methodology. WEI completed the research, developed and tested a methodology, and discussed it with Watermaster staff earlier this year. WEI was subsequently directed to apply the methodology to estimate evaporative losses for all of the recharge facilities. This technical memorandum summarizes the technical work done to date, preliminary findings, and recommendations for finalizing the work.
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Technical Memorandum
To: Peter Kavounas
From: Garrett Rapp, Mark Wildermuth
Date: September 18, 2017
Subject: Estimation of Evaporation Losses in Recharge Facilities in the Chino Basin
Background and Objective The Chino Basin Watermaster (Watermaster), Chino Basin Water Conservation District (CBWCD), and Inland Empire Utilities Agency (IEUA) operate recharge facilities in the Chino Basin for storm, recycled, and imported waters (hereafter, recycled and imported waters are collectively referred to as supplemental water). Figure 1 shows the locations of these recharge facilities and the types of water recharged. Table 1 lists IEUA estimates of the annual recharge of storm and supplemental water at these facilities for the period of July 2011 through June 2016. These recharge estimates were made assuming that evaporative losses were negligible.
Watermaster is interested in determining the magnitude and significance of evaporative losses for storm and supplemental water diverted into the recharge facilities for recharge into the Chino Basin. If Watermaster were to determine that evaporative losses are significant, it would like to establish a method to estimate and apply evaporative losses to storm and supplemental water deliveries to more accurately estimate recharge. Specifically, Watermaster staff is interested in determining if a “postage stamp” evaporation loss rate could be developed that would enable it to assess evaporation losses on all water delivered to recharge facilities.
Watermaster directed WEI to: identify sources of data that could be used to estimate evaporative losses from water stored in recharge facilities in the Chino Basin, develop a methodology to estimate evaporation losses at the recharge facilities, and conduct a proof of concept of the methodology. WEI completed the research, developed and tested a methodology, and discussed it with Watermaster staff earlier this year. WEI was subsequently directed to apply the methodology to estimate evaporative losses for all of the recharge facilities. This technical memorandum summarizes the technical work done to date, preliminary findings, and recommendations for finalizing the work.
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Data and Methodology There are two methods to compute evaporation from a free water surface: energy budget and empirical methods. Energy budget methods require detailed site‐specific information measured at each recharge facility; this information does not exist in the Chino Basin area. Empirical methods are based on the direct measurement of evaporation in evaporation pans and converting those measurements to evaporation estimates. The latter method was adopted herein. The data required to estimate evaporation losses at recharge facilities using an evaporation pan are described below.
1. Daily evaporation data – WEI researched available evaporation data within and proximate to the Chino Basin and acquired evaporation data from two evaporation monitoring stations:
a. Puddingstone Reservoir (San Dimas): This evaporation pan is located at Puddingstone Reservoir. It is a screened land pan and is operated by the Los Angeles County Department of Public Works (LACDPW). The pan is at an elevation of 1030 feet above mean sea level (ft‐amsl). LACDPW staff take daily evaporation measurements at this station.
b. Lake Mathews (Riverside): This evaporation pan is located at Lake Mathews. It is a Class A pan and is operated by the Metropolitan Water District of Southern California (MWDSC). The pan is at an elevation of 1470 ft‐amsl. MWDSC staff take weekly measurements at this station.
Figure 1 shows the locations of these evaporation measurement stations in relation to the Chino Basin and the recharge facilities. Upon review of the data, WEI chose to use the Puddingstone Reservoir evaporation data because its evaporation pan is located closer to the Chino Basin recharge facilities and its elevation is more representative of the Chino Basin recharge facilities than the evaporation pan at Lake Mathews. The recharge facilities range in elevation between about 750 ft‐amsl (Grove Basin) to about 1480 ft‐amsl (San Sevaine Basin 1). Furthermore, the daily evaporation measurements from Puddingstone Reservoir enable more accurate evaporation estimates than could be achieved using the weekly evaporation measurements from Lake Matthews. Figure 2 shows the monthly evaporation time history measured at Puddingstone Reservoir for the period of July 2011 through June 2016.
2. Elevation‐Area‐Storage tables – The IEUA developed elevation‐area‐storage (EAS) tables for each recharge facility based on land and photogrammetric surveys. The EAS tables contain the relationship of elevation to water surface area and storage for each recharge facility. The IEUA uses stage time‐history data measured at water level sensors and EAS tables for each recharge facility to develop estimates of stormwater capture and infiltration rates.
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3. Stage data – The IEUA measures stage at recharge facilities with water level sensors and acquires the measurements through a Supervisory Control and Data Acquisition (SCADA) system. WEI collected stage time‐history data for the recharge facilities for the period of July 1, 2011 through June 30, 2016.
4. Historical stormwater capture and supplemental water deliveries to recharge facilities – The IEUA tabulates the amount of stormwater capture and supplemental water deliveries to each facility in a Microsoft Excel workbook and uses this data to create monthly summaries of recharge. The tabulations also include notes that characterize the specific operations of each recharge facility. While the IEUA tabulation describes the monthly stormwater captured and supplemental water deliveries to each recharge facility, the recharge of this water may not occur during the period that the water enters the recharge facility. Storm and supplemental water can enter the recharge facilities at rates that exceed the infiltration rates and remain in storage for several months.
The steps used to estimate evaporative losses from water diverted into recharge facilities are described below.
1. Selection of recharge facilities for the estimation of evaporative losses – Based on the review of available data for estimating evaporation losses, all the recharge facilities listed in Table 1 except the College Heights and Etiwanda Debris Basins were selected for analysis. The College Heights Basins were excluded because the instrumentation is not sufficient to estimate evaporative losses. And, the Etiwanda Debris Basin was excluded because it does not have the instrumentation required to estimate stage.
2. Investigation period – The period July 1, 2011 through June 30, 2016 was selected for the investigation of evaporation losses. This period includes a uniquely large imported water delivery event of about 22,500 acre‐feet (AF) to 14 recharge facilities over the period of July 2011 through October 2011 and consistent recycled water recharge at several facilities.
3. Development of stage time series – The stage time series data from the IEUA were compiled for each facility in a Microsoft Excel workbook. The beginning‐of‐day stage measurements for each facility were plotted and reviewed to assess completeness and reasonableness. Some data were adjusted to fill gaps or to adjust for obvious errors.
4. Computation of average daily water surface area – The average daily surface area for each recharge facility was estimated from stage data and the EAS tables.
5. Computation of evaporation loss – For each recharge facility, the daily evaporation loss, expressed volumetrically in AF, was computed by multiplying the average
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daily water surface area by the daily evaporation measured at the Puddingstone Reservoir using the following equation:
∗12
Where is the daily evaporative loss in AF, is the average water surface
area in acres, and is the measured daily evaporation in inches.
6. Computation of monthly and annual evaporation loss rates by recharge facility – The evaporation loss rate, as referred to herein, is the evaporation expressed as a ratio of the volumetric evaporation loss divided by the sum of initial storage plus storm water captured plus supplemental water delivered, expressed as a percentage. The daily evaporation losses calculated in step 5 were aggregated by month and fiscal year to calculate the evaporation loss rate using the following equation:
∑
∑∗ 100%
Where is the monthly/annual evaporative loss rate, ∑ is the sum of the daily evaporation losses for the month/year in AF, is the storage in the recharge facility at the beginning of the month/year in AF, and ∑ is the sum of diverted water from all sources to the recharge facility in the month/year in AF.
Results and Discussion
Evaporative Losses Table 2 shows the annual evaporation loss rates for each of the recharge facilities during the analysis period. The Brooks Street and Ely recharge facilities were the only recharge facilities to have enough data to compute evaporation loss and loss rate estimates for all five years in the investigation period. Comparing annual evaporation loss rate estimates for all recharge facilities in the investigation period indicates that the annual evaporation loss rate varies from a minimum of 0.2 percent for the Lower Day Basin in FY2015 to a maximum of 9.7 percent for Turner Basins 3 and 4 in FY2013. The annual volume‐weighted evaporation loss rate ranges from 2.7 percent to 3.2 percent and averages about 3.0 percent. There are 80 potential evaporation loss rates that could have been computed in the investigation period (16 recharge facilities times five years) had the stage data been available and useful. 30 of the potential evaporation loss rates could not be estimated due to data challenges.
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Tables 3a through 3n show the July 1 initial storage, the annual inflow volumes of stormwater capture and supplemental water deliveries, the estimated annual evaporation loss, and the annual evaporation loss rate for each recharge facility summarized in Table 2.
Tables 4a through 4n are similar to Tables 3a through 3n and show, on a monthly time step, the initial monthly storage, volumes of stormwater capture, supplemental water deliveries, and estimated monthly evaporation loss.
The wide variability in the evaporation rates among the recharge facilities and over time are attributed to the following:
1. Data challenges as previously described.
2. Infiltration rate – A higher infiltration rate will result in less water lost to evaporation. For example, consider the evaporation loss rates for RP3 Basins 1, 3, and 4, and Victoria Basin. Both facilities receive recharge throughout the year. The estimated evaporation loss rate in RP3 Basins 1, 3, and 4 is about 2.0‐2.5 percent; these basins have typical infiltration rates exceeding one foot per day. Victoria Basin has infiltration rates typically below 0.5 feet per day and estimated evaporation loss rates of 6.0 percent or greater.
3. Timing and magnitude of stormwater capture and supplemental water deliveries – Water diverted into recharge facilities in the summer will experience greater evaporation losses than water diverted in the winter. This is due to higher evaporation rates in the summer months. For example, the sums of initial storage and water diverted into the Brooks Street Basin were 316 AF and 313 AF in July 2013 and February 2014, respectively (see Table 4c), and the volumes of evaporation losses in July 2013 and February 2014 for the Brooks Street Basin were 5.4 AF and 1.9 AF, respectively. The July evaporative losses were almost three times the February evaporation losses.
The importance of the timing of stormwater capture and supplemental water delivery on evaporation loss can be seen from the monthly evaporation losses shown in Tables 4a through 4n and Figures 3a through 3e. Figures 3a through 3e show the estimated volume‐weighted monthly evaporation loss rates for the investigation period for the Brooks Street Basin, Ely Basins, Hickory Basin, RP3 Basins (1, 3, and 4), and Victoria Basin, respectively. Figure 3f shows the monthly volume‐weighted average evaporation loss rate for these recharge facilities. The average monthly volume‐weighted evaporative loss rates range from a minimum of 0.78 percent (January) to 3.75 percent (August), and the volume‐weighted annual evaporative loss rate is about 3.0 percent.
Seasonal Evaporation Losses In addition to the annual evaporation loss rate estimates, Watermaster directed WEI to develop seasonal postage stamp evaporation loss rate estimates using the daily
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evaporation losses that were used for the annual estimates. WEI reviewed the monthly data and divided the year into a wet season from November through March and a dry season for the rest of the year. WEI developed these seasonal evaporation loss rates for the recharge facilities for which average monthly evaporation loss rates were calculated and shown in Figures 3a through 3e: Brooks Street Basin, Ely Basins, Hickory Basin, RP3 Basins (1, 3, and 4), and Victoria Basin.
Table 5 shows that for the five basins analyzed, the average wet season evaporation loss rate ranges from 0.9 percent to 4.2 percent, and the volume‐weighted average is about 1.5 percent. The dry season evaporation loss rate ranges from 2.7 percent to 5.9 percent, and the volume‐weighted average is about 4.2 percent.
Limitations There are limitations to this work that create uncertainty in the results presented above. These limitations, described below, can be addressed in future work.
1. The stage time‐series data for the recharge facilities are not always reliable, and in some cases, the level sensors are not vertically located to measure stage and evaporative losses.The challenges with the water level sensors also impact the IEUA’s ability to accurately estimate stormwater capture and recharge. This limitation can be overcome through improvements in the deployment and maintenance of the water level sensors.
2. The five‐year period of record analyzed is short and contains highly variable amounts of stormwater capture and supplemental water deliveries. The evaporation loss rates based on the data available during this period may not be statistically defensible. Note that the evaporation measurement record at Puddingstone Reservoir runs from the 1950s to present and that the Chino Basin Wasteload Allocation Model (WLAM) was calibrated in 2016 to match the stormwater capture and recharge estimates developed by the IEUA. As such, the limitation posed by the five‐year investigation period and the uncertainty of the timing and magnitude of future diversions to recharge facilities could be eliminated by estimating evaporative losses for planning scenarios with the Chino Basin Wasteload Allocation Model.
3. The evaporation losses for the recharge facilities are based on evaporation estimates from Puddingstone Reservoir, which is located west and outside of the Chino Basin Watershed. More accurate estimates of evaporation losses would be assured if one or more evaporation stations were established in the Chino Basin.
Conclusions Evaporation losses vary significantly over time at each recharge facility. This variability is caused by seasonal variability in evaporation, temporal and spatial variability in the water diverted into recharge facilities, temporal and spatial variability of infiltration rates and
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the availability of useable stage data at the recharge facilities. Across the entire watershed for all years analyzed, the average annual evaporation loss rate is about 3.0 percent, varying between a low of 2.7 percent in FY2012 to a high of 3.2 percent in FY2013. Although the timing, volume, and location of water capture and delivery in these recharge facilities fluctuate throughout the five‐year analysis period, the total volume‐weighted annual values are within a relatively narrow range, compared to fluctuations between years at each recharge facility.
The recharge facilities with the most consistent use throughout the year include the Brooks Street Basin, Ely Basins, Victoria Basin, Hickory Basin, and RP3 Basins (1, 3, and 4). The annual volume‐weighted evaporative loss rate for these basins is also 3.0 percent. The volume‐weighted average evaporation loss rates for these recharge facilities are 1.5 percent for the wet season of November through March and 4.2 percent for the rest of the year.
However, as discussed above, the variability of evaporation losses is controlled by the time of year in which the stormwater capture or supplemental water delivery occurs and the temporal variability in deliveries and infiltration rates. Variability is also caused by challenges in the availability of useful stage data at recharge facilities.
Recommendations The following recommendations are based on the work documented herein:
1. Based on the available data and usage pattern of the recharge facilities, Watermaster should consider the adoption of the seasonal evaporation loss rates of 1.5 and 4.2 percent for the wet and dry seasons, respectively. This bifurcation captures the seasonal effects on evaporation and will allow for a more accurate accounting of supplemental water recharge losses in the future.
2. Relocate and/or replace water level sensors where stage data are insufficient and or unreliable. Implementing a pro‐active water level sensor replacement program will minimize data loss due to sensor failure and increase the availability of usable data for future evaporation loss evaluations and other investigations.
Attachments Tables 1, 2, 3a‐3n, 4a‐4n, and 5; Figures 1, 2, and 3a‐3f
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Recharge Basins in the Chino Basinand Proximate Evaporation Stations
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Date: 7/20/2017
Author: GAR
Name: Figure_1_rech
Recharge Basins(Symbolized by Recharged Water Type
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