CHAPTER 3 – Population and Demand Forecast
Accurate data about projected water demand is essential for long-term water system planning. This chapter presents the Utility’s forecasts of population, households, employment and water demand. Following a review of historical and projected demographic data is a summary of use characteristics including production, consumption and related factors. The chapter concludes with a demand forecast for the next 50 years based on the demographics, water supply characteristics and related uncertainties.
3.1 DEMOGRAPHIC DATA
Demographic data presented here includes total population, number of single-family and multi-family households and total employment. Table 3.1 shows the historical and projected demographics at specific planning horizons from 2015 to 2064.
Forecasts are based on the Thurston Regional Planning Council (TRPC) November 2012 data set. See Appendix 3-1 for more information on how these demographics were developed and a breakdown of the demographics by pressure zone.
Year |
Population |
Single-Family Households |
Multi-family Households |
Employment |
---|---|---|---|---|
2015 (Plan Year 1) |
62,097 |
17,144 |
11,601 |
58,840 |
2020 (Plan Year 6) |
68,011 |
18,147 |
13,644 |
62,825 |
2034 (Plan Year 20) |
83,388 |
22,122 |
17,595 |
73,981 |
2064 (Plan Year 50) |
113,427 |
29,815 |
25,600 |
102,026 |
3.2 Water Use Characteristics
This section describes the water use characteristics used in making the demand forecast:
• Production and peaking factor
• Customer categories and consumption
• Non-revenue water and leakage
• Water use factors and ERUs
Production and Peaking Factor
Olympia produces water from the McAllister Wellfield and six wells, as described in Chapter 4. Before the McAllister Wellfield came online in October 2014, Olympia obtained the majority of its drinking water from McAllister Springs. Table 3.2 shows average production over the last three years, by source and by month. The total average annual production has been 2,581 million gallons (Mg). Of that, 77 percent was derived from McAllister Springs (2010-2012) average. As is typical with most water utilities, production peaks in the summer months of May through October.
Figure 3.1 and Figure 3.2 show this same information graphically, and Figure 3.3 shows the annual production for each year from 2003 to 2012.
Month |
McAllister Springs (S01) |
Kaiser Well 1 (S03) |
Hoffman Well 3 (S08) |
Allison Well 13 (S09) |
Shana Park Well 11 (S10) |
Allison Well 19 (S11) |
Indian Summer 20 (S12) |
Total |
Percent |
---|---|---|---|---|---|---|---|---|---|
Jan |
148.5 |
0.0 |
0.0 |
9.2 |
12.0 |
9.0 |
0.2 |
178.8 |
7% |
Feb |
140.4 |
0.0 |
0.0 |
3.6 |
17.0 |
4.9 |
0.2 |
166.2 |
6% |
Mar |
152.6 |
3.1 |
0.0 |
3.9 |
20.5 |
5.4 |
0.2 |
185.7 |
7% |
Apr |
151.2 |
4.2 |
0.0 |
3.8 |
19.7 |
5.9 |
0.2 |
185.0 |
7% |
May |
154.3 |
7.1 |
0.0 |
11.3 |
23.4 |
11.1 |
0.3 |
207.4 |
8% |
Jun |
170.8 |
8.7 |
0.0 |
13.9 |
17.9 |
13.9 |
5.1 |
230.2 |
9% |
Jul |
205.1 |
9.2 |
0.0 |
17.6 |
25.4 |
22.1 |
19.1 |
298.5 |
11% |
Aug |
219.0 |
4.6 |
0.0 |
20.9 |
34.8 |
25.4 |
19.4 |
324.1 |
12% |
Sep |
170.4 |
0.8 |
0.0 |
16.4 |
32.1 |
23.1 |
7.8 |
250.5 |
10% |
Oct |
132.6 |
3.0 |
0.0 |
13.0 |
26.0 |
15.5 |
0.0 |
190.2 |
7% |
Nov |
168.6 |
0.0 |
0.0 |
5.1 |
5.1 |
8.5 |
0.1 |
187.5 |
7% |
Dec |
167.5 |
0.0 |
0.0 |
4.1 |
0.2 |
5.3 |
0.0 |
177.1 |
7% |
Total |
1,981 |
41 |
0.08 |
123 |
234 |
150 |
53 |
2,581 |
100% |
Percent |
77% |
2% |
0.003% |
5% |
9% |
6% |
2% |
100% |
|
Note: Ten years of production data was analyzed. However, this table uses the most recent three years in order to focus on current trends. |
View Figure 3.1 Water Production by Source (2010 – 2012 Average).
View Figure 3.2 Water Production Monthly Distribution (2010 – 2012 Average).
View Figure 3.3 Annual Production (2003 – 2012).
Table 3.3 gives the peaking factors from 2003 to 2012. The peaking factor has ranged from 1.6 to 2.5, and has averaged 1.7 for the most recent three years. Note that the demand forecast presented later in this chapter uses a slightly higher peaking factor of 2.0 for the current year (2013). This is approximately halfway between the average of the most recent three years and 2.3, which Olympia used in its 2009 Water System Plan.
Table 3.3 shows that the peaking factor has trended downward. To incorporate this decreasing trend in the peaking factor, a 0.3 percent annual decrease is applied to the peaking factor each year until the end of the forecast period.
Year |
Average Day (Mgd) |
Peak Day |
Peaking Factor |
|
---|---|---|---|---|
(Mgd) |
Date |
|||
2003 |
8.0 |
15.6 |
7/29/2003 |
2.0 |
2004 |
7.7 |
19.5 |
7/20/2004 |
2.5 |
2005 |
7.8 |
15.0 |
8/6/2005 |
1.9 |
2006 |
8.6 |
16.1 |
7/6/2006 |
1.9 |
2007 |
8.6 |
15.1 |
7/11/2007 |
1.8 |
2008 |
8.3 |
13.8 |
8/15/2008 |
1.7 |
2009 |
8.1 |
15.9 |
7/29/2009 |
1.9 |
2010 |
7.1 |
12.5 |
8/14/2010 |
1.8 |
2011 |
7.2 |
11.7 |
8/4/2011 |
1.6 |
2012 |
7.0 |
11.6 |
8/15/2012 |
1.7 |
2010-2012 Avg |
7.07 |
11.92 |
n/a |
1.7 |
Note: Data is presented for ten years to show a lengthy history. |
Customer Categories and Consumption
Olympia has six retail customer categories. Each category has standard connections and irrigation-only connections.
• Single-family. Detached residential buildings serving a single family, duplex, triplex or four-plex.
• Multi-family. Residential buildings such as apartment buildings or condominiums that serve multiple households.
• Commercial. Business and governmental customers.
• Municipal. City of Olympia facilities.
• Political subdivision. Includes quasi-governmental customers such as Intercity Transit, Port of Olympia and schools.
• State. State of Washington facilities.
The City also sells water wholesale to the City of Lacey and Thurston Public Utility District No. 1 (PUD). Prior to June 2005, Olympia provided retail service to customers in the PUD’s service area. From 2005-2015, Olympia sold water wholesale to the PUD, which in turn provided water service to its customers. Over the past several years the PUD has moved toward securing its own water supply and plans to stop purchasing wholesale water from Olympia completely in early 2015.
The amount of water expected to be wholesaled to the City of Lacey was developed based on the wholesale agreement with Lacey. The agreement states that Olympia will provide Lacey with up to 2 Mgd from November to June and up to 1 Mgd from July to October. The agreement is valid until December 31, 2016. After this date, the demand associated with Lacey is assumed to be zero.
Table 3.4 gives the number of connections for each customer category from 2003 to 2012. Most connections are either single-family (86%) or commercial (9%).
Average consumption, by customer category and by month, over the last three years, is shown in Table 3.5. The largest share of water consumption is accounted for by the single-family customer category (40%), followed by commercial (20%), and multi-family (15%). These collectively represent 75 percent of consumption.
Figure 3.4 and Figure 3.5 show the same information as Table 3.5, graphically.
Actual monthly consumption of water may differ slightly from the data presented in Table 3.5 and Figures 3.4 and Figure 3.5. Most water meters are read bi-monthly and consumption is assigned to the month in which the meter is read.
Customer Category |
Number of Connections |
|||||||||||
---|---|---|---|---|---|---|---|---|---|---|---|---|
2003 |
2004 |
2005 |
2006 |
2008 |
2009 |
2010 |
2011 |
2012 |
2010-2012 Avg |
|||
# |
% |
|||||||||||
1. Single-family |
Standard |
14,768 |
15,122 |
15,201 |
15,492 |
14,648 |
14,905 |
15,284 |
15,625 |
15,962 |
15,624 |
85% |
Irrigation |
161 |
161 |
166 |
170 |
60 |
65 |
63 |
63 |
69 |
65 |
0.4% |
|
Total |
14,929 |
15,283 |
15,367 |
15,662 |
14,708 |
14,970 |
15,347 |
15,688 |
16,031 |
15,689 |
86% |
|
2. Multi-family |
Standard |
610 |
622 |
643 |
644 |
666 |
688 |
702 |
709 |
720 |
710 |
4% |
Irrigation |
18 |
20 |
22 |
22 |
21 |
24 |
23 |
29 |
30 |
27 |
0.1% |
|
Total |
628 |
642 |
665 |
666 |
687 |
712 |
725 |
738 |
750 |
738 |
4% |
|
3. Commercial |
Standard |
1,495 |
1,510 |
1,528 |
1,549 |
1,402 |
1,415 |
1,427 |
1,424 |
1,427 |
1,426 |
8% |
Irrigation |
259 |
271 |
282 |
291 |
228 |
237 |
238 |
243 |
251 |
244 |
1.3% |
|
Total |
1,754 |
1,781 |
1,810 |
1,840 |
1,630 |
1,652 |
1,665 |
1,667 |
1,678 |
1,670 |
9% |
|
4. Municipal |
Standard |
58 |
57 |
55 |
56 |
55 |
54 |
53 |
58 |
60 |
57 |
0.3% |
Irrigation |
50 |
50 |
48 |
53 |
10 |
10 |
12 |
13 |
16 |
14 |
0.1% |
|
Total |
108 |
107 |
103 |
109 |
65 |
64 |
65 |
71 |
76 |
71 |
0.4% |
|
5. Political Subdivision |
Standard |
59 |
60 |
60 |
61 |
55 |
55 |
55 |
58 |
64 |
59 |
0.3% |
Irrigation |
30 |
30 |
32 |
32 |
13 |
13 |
13 |
14 |
13 |
13 |
0.1% |
|
Total |
89 |
90 |
92 |
93 |
68 |
68 |
68 |
72 |
77 |
72 |
0.4% |
|
6. State |
Standard |
94 |
95 |
97 |
97 |
58 |
57 |
62 |
63 |
63 |
63 |
0.3% |
Irrigation |
50 |
53 |
56 |
56 |
30 |
31 |
32 |
35 |
36 |
34 |
0.2% |
|
Total |
144 |
148 |
153 |
153 |
88 |
88 |
94 |
98 |
99 |
97 |
0.5% |
|
Total |
Standard |
17,084 |
17,466 |
17,584 |
17,899 |
16,884 |
17,174 |
17,583 |
17,937 |
18,296 |
17,939 |
98% |
Irrigation |
568 |
585 |
606 |
624 |
362 |
380 |
381 |
397 |
415 |
398 |
2% |
|
Total |
17,652 |
18,051 |
18,190 |
18,523 |
17,246 |
17,554 |
17,964 |
18,334 |
18,711 |
18,336 |
100% |
Customer Category |
Jan |
Feb |
Mar |
Apr |
May |
Jun |
Jul |
Aug |
Sep |
Oct |
Nov |
Dec |
Total |
Percent |
|
---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|
1. Single-family |
Standard |
51 |
74 |
56 |
60 |
65 |
86 |
56 |
148 |
82 |
113 |
56 |
77 |
923 |
39% |
Irrigation |
0.03 |
0.02 |
0.03 |
0.04 |
0.02 |
1.25 |
0.41 |
9.85 |
2.65 |
7.80 |
0.39 |
0.14 |
23 |
1% |
|
Total |
51 |
74 |
56 |
60 |
65 |
87 |
56 |
158 |
85 |
121 |
57 |
77 |
946 |
40% |
|
2. Multi-family |
Standard |
23 |
31 |
25 |
26 |
27 |
32 |
24 |
39 |
28 |
34 |
28 |
31 |
348 |
15% |
Irrigation |
0 |
0 |
0 |
0 |
0 |
1 |
1 |
3 |
3 |
3 |
1 |
0 |
12 |
0% |
|
Total |
23 |
31 |
25 |
26 |
27 |
33 |
26 |
42 |
31 |
36 |
29 |
31 |
360 |
15% |
|
3. Commercial |
Standard |
33 |
29 |
34 |
25 |
39 |
30 |
35 |
37 |
41 |
31 |
39 |
28 |
402 |
17% |
Irrigation |
0 |
0 |
0 |
0 |
1 |
5 |
8 |
25 |
16 |
19 |
3 |
1 |
79 |
3% |
|
Total |
33 |
30 |
34 |
25 |
40 |
36 |
42 |
61 |
57 |
50 |
42 |
29 |
481 |
20% |
|
4. Municipal |
Standard |
1 |
1 |
1 |
0 |
1 |
1 |
1 |
1 |
2 |
1 |
1 |
1 |
11 |
0% |
Irrigation |
0.1 |
0.0 |
0.1 |
0.2 |
0.5 |
1.3 |
1.8 |
4.4 |
3.5 |
2.5 |
1.0 |
0.1 |
16 |
1% |
|
Total |
1 |
1 |
1 |
1 |
2 |
2 |
3 |
6 |
5 |
3 |
2 |
1 |
27 |
1% |
|
5. Political Subdivision |
Standard |
4 |
5 |
4 |
5 |
4 |
5 |
5 |
7 |
5 |
5 |
6 |
5 |
60 |
3% |
Irrigation |
0.1 |
-0.1 |
0.2 |
0.1 |
0.6 |
2.2 |
3.0 |
7.0 |
3.7 |
3.0 |
1.2 |
0.4 |
21 |
1% |
|
Total |
4 |
5 |
4 |
5 |
5 |
7 |
8 |
14 |
9 |
8 |
7 |
5 |
82 |
3% |
|
6. State |
Standard |
3 |
6 |
5 |
3 |
6 |
7 |
5 |
9 |
4 |
6 |
8 |
5 |
66 |
3% |
Irrigation |
0.0 |
0.0 |
0.0 |
0.1 |
0.0 |
0.5 |
1.0 |
5.7 |
5.8 |
3.3 |
0.3 |
0.0 |
17 |
1% |
|
Total |
3 |
6 |
5 |
3 |
6 |
7 |
6 |
14 |
10 |
9 |
8 |
5 |
83 |
4% |
|
7. Billed Construction Sites |
0.3 |
0.3 |
0.3 |
0.3 |
0.3 |
0.3 |
0.3 |
0.3 |
0.3 |
0.3 |
0.3 |
0.3 |
3 |
0% |
|
8. Lacey Wholesale |
17.8 |
18.1 |
27.6 |
26.2 |
26.0 |
27.9 |
30.9 |
31.8 |
23.2 |
20.2 |
20.2 |
20.9 |
291 |
12% |
|
9. PUD Wholesale |
7.9 |
7.6 |
9.7 |
11.1 |
11.3 |
11.3 |
7.1 |
7.2 |
5.5 |
3.8 |
3.6 |
3.3 |
89 |
4% |
|
Total |
Standard |
115 |
147 |
124 |
120 |
142 |
160 |
126 |
241 |
163 |
190 |
139 |
146 |
1,815 |
77% |
Irrigation |
0 |
0 |
1 |
1 |
2 |
11 |
15 |
55 |
35 |
39 |
6 |
2 |
167 |
7% |
|
Wholesale |
26 |
26 |
37 |
37 |
37 |
39 |
38 |
39 |
29 |
24 |
24 |
24 |
380 |
16% |
|
Total |
141 |
173 |
162 |
158 |
182 |
211 |
179 |
335 |
226 |
253 |
170 |
172 |
2,362 |
100% |
|
Percent |
6% |
7% |
7% |
7% |
8% |
9% |
8% |
14% |
10% |
11% |
7% |
7% |
100% |
|
|
View Figure 3.4 Monthly Distribution of Water Consumption (2010 – 2012 Average).
View Figure 3.5 Water Consumption by Customer Category (2010 – 2012 Average).
Comparing the percent of connections to the percent of consumption can be useful, since water consumption does not always follow the same proportion as customer connections. This comparison is shown in Figure 3.6, which focuses on retail deliveries. Three customer categories stand out in this comparison. Single-family has a much larger percent of connections (86%) compared to the percent of retail consumption (48%). Multi-family has a much smaller percent of connections (4%) compared to the percent of retail consumption (18%). This is because one multi-family connection serves many multi-family households. Commercial has a much smaller percent of connections (9.1%) compared to retail consumption (24%).
View Figure 3.6 Retail Connections and Consumption Comparison (2010 – 2012 Average).
Customers with large water demand are of interest since their demand could have significant impact on overall demand. This is particularly true when the largest customers are commercial and industrial customers. Table 3.6 summarizes water use for the customers with the highest water use for 2011 and 2012.
Given the nature of these customers, any changes in their future demand would likely be reflected in the demographic projections; therefore no special treatment of these customers was used for the demand forecast.
Rank |
Customer Name |
Service Address |
Total Consumption (Mg) |
---|---|---|---|
1 |
Crown Beverage & Packaging Company |
1202 Fones Road SE |
41.5 |
2 |
St Peters Hospital |
413 Lilly Road NE |
33.2 |
3 |
Evergreen State College |
2700 Evergreen Parkway NW |
33.1 |
4 |
Olympia School District #111 |
Multiple Locations |
28.7 |
5 |
LOTT Clean Water Alliance |
500 Adams Street NE |
26.1 |
6 |
Cambridge Court Apartments |
2323 9th Avenue SW |
17.0 |
7 |
Black Lake LLC |
1900 Black Lake Boulevard SW |
16.5 |
8 |
Capital Medical Center |
3900 Capital Mall Drive SW |
16.5 |
9 |
City Of Olympia Parks |
Multiple Locations |
14.6 |
10 |
Colonial Estates |
3601 18th Avenue SE |
13.5 |
11 |
Capitol Building & Grounds |
Multiple Locations |
13.4 |
12 |
Courtside Apartments |
515 Courtside Street SW |
13.1 |
13 |
Bellwether Apartments 2 |
1400 Fones Road SE |
12.6 |
14 |
Apple Park Apartments |
3200 Capital Mall Drive SW |
12.4 |
15 |
Thurston County Facilities 1 |
2000 Lakeridge Drive SW |
11.7 |
16 |
Extendicare Health/Assisted |
430 Lilly Rd Ne/4001 Capital Mall Drive SW |
11.2 |
17 |
Olympic Heights Apartments 2 |
300 Kenyon Street NW |
10.3 |
18 |
Western Heritage / Coopers Glen 2 |
3138 Overhulse Road NW |
9.6 |
Total |
335.0 |
||
Percent |
100% |
||
Non-Revenue Water and Leakage
The forecast of future demand includes a calculation of “non-revenue water,” which includes leakage and all other unmetered and metered uses that are not sold for revenue. Authorized uses of unmetered (and therefore, unbilled) water include firefighting and hydrant flushing, sampling, water and sewer line flushing and testing, street cleaning and other maintenance. For this purpose, a simple calculation of production minus sales was used to determine non-revenue water, as shown in Table 3.7. Distribution System Losses (DSL) aredetermined by subtracting unbilled authorized use from non-revenue water. Figure 3.7 graphically shows distribution system losses for the last four years compared to the four-year average.
Year |
Production1 |
Sales2 |
Unbilled Authorized Use |
Distribution System Losses |
Non-Revenue Water |
||||
---|---|---|---|---|---|---|---|---|---|
Qty3 |
Percent of Production |
Qty4 |
Percent of Production |
Qty5 |
Percent of Production |
Percent of Sales |
|||
2004 |
2,809 |
2,581 |
41 |
1.5% |
187 |
6.7% |
228 |
8.1% |
8.85% |
2005 |
2,832 |
2,616 |
41 |
1.5% |
175 |
6.2% |
217 |
7.6% |
8.28% |
2006 |
3,129 |
2,757 |
46 |
1.5% |
327 |
10.4% |
372 |
11.9% |
13.51% |
2007 |
3,074 |
2,713 |
45 |
1.5% |
316 |
10.3% |
361 |
11.7% |
13.31% |
2008 |
3,030 |
2,662 |
-- |
-- |
-- |
-- |
368 |
12.2% |
13.84% |
2009 |
2,973 |
2,651 |
15 |
0.5% |
307 |
10.3% |
322 |
10.8% |
12.13% |
2010 |
2,573 |
2,355 |
14 |
0.5% |
204 |
7.9% |
218 |
8.5% |
9.25% |
2011 |
2,611 |
2,433 |
27 |
1.0% |
151 |
5.8% |
178 |
6.8% |
7.31% |
2012 |
2,559 |
2,297 |
18 |
0.7% |
244 |
9.5% |
262 |
10.2% |
11.41% |
2010-2012 Average6 |
2,581 |
2,362 |
20 |
0.8% |
200 |
7.7% |
219 |
8.5% |
9.3% |
View Figure 3.7 Distribution System Losses (2009 – 2012).
Water Use Factors and ERUs
Water use factors were calculated for three customer categories: single-family; multi-family; and industrial, commercial and institutional (ICI). Table 3.8 shows the data used for the calculations, including the number of Equivalent Residential Units (ERUs) in each customer category.
ERUs are a method of representing water use by non-residential customers as an equivalent number of residential customers. An ERU is the amount of water used by a single-family household, which in Olympia averages 166 gallons per day (gpd). The number of ERUs for each customer category is obtained by dividing the consumption (in gpd) for a customer category by 166. Therefore, the single-family customer category equates to 15,624 ERUs; the multi-family category to 5,940 ERUs; and the industrial, commercial, institutional category to 11,099 ERUs.
Below are the key water use factors and how they were calculated:
• 166 gpd per single-family household. Single-family consumption (2,591,885 gpd) divided by the number of households (15,624).
• 92 gpd per multi-family household. Multi-family consumption (986,023 gpd) divided by the number of households (10,748).
• 33 gpd per employee. Industrial, commercial, institutional consumption (1,842,518 gpd) divided by the number of employees (55,834).
Water use factors have trended downward in the last decade. To incorporate the downward trend in water use factors, the forecast assumes a 0.3% annual decrease in the water use factors for single-family residential and multi-family residential throughout the forecast period. Due to the variability in ICI demand, the water use factor for ICI remains the same throughout the forecast period.
Customer Category |
Sales (gpd)1 |
Households or Employees |
Sales Per Household or Employee (gpd) |
Number of ERUs5 |
||
---|---|---|---|---|---|---|
Residential |
||||||
Single-family (SF) |
2,591,885 |
15,624 |
2 |
166 |
4 |
15,624 |
Multi-family (MF) |
986,023 |
10,748 |
3 |
92 |
|
5,940 |
Non-Residential |
||||||
Commercial |
1,317,595 |
39,927 |
6 |
33 |
7 |
7,937 |
Municipal |
73,963 |
2,241 |
6 |
33 |
7 |
446 |
Political Subdivision |
223,799 |
6,782 |
6 |
33 |
7 |
1,348 |
State |
227,161 |
6,884 |
6 |
33 |
7 |
1,368 |
Lacey Wholesale |
796,596 |
N/A |
|
N/A |
|
4,799 |
PUD Wholesale |
245,136 |
N/A |
|
N/A |
|
1,477 |
Unbilled Authorized Use |
53,777 |
N/A |
|
N/A |
|
324 |
Distribution System Leakage |
547,082 |
N/A |
|
N/A |
|
3,296 |
Total ERUs |
42,560 |
|||||
|
|
|||||
3.3 Demand Forecast
Olympia’s Comprehensive Plan requires the Utility to reserve water supply rights for at least 50 years in advance of need, so that supplies can be protected from contamination or commitment to lower priority uses (Policy PU 5.1). This section describes the methodology used in developing the demand forecast and provides the results with and without additional conservation.
Demand Forecast Methodology
The methodology used to develop the demand forecast for retail consumption is illustrated in Figure 3.8. The basic process is to combine demographic data with water use factors to calculate customer demands. Demand components for non-revenue water, the PUD wholesale water and Lacey wholesale water are then added to create the total average day demand (ADD). To generate the total maximum day demand, a peaking factor is applied to all demands except the Lacey and PUD demands. See Appendix 3-1, Planning Data and Demand Forecast Technical Memorandum from HDR Engineering, Inc., for more information on the methodology.
View Figure 3.8 Demand Forecast Methodology.
Demand Forecast with and without Conservation
Projected demand for average day and maximum day are shown in Table 3.9 and Figure 3.9, with and without additional conservation. Additional conservation as shown reflects what demand would look like if conservation goals are met (Chapter 5). Figure 3.10 shows the six components of the average day demand in order to illustrate the relative impact of each component. The decrease in demand in 2017 reflects the end of the City’s wholesale water agreement with the PUD in early 2015 and the end of the agreement with Lacey in December 2016. Beyond 2017, demand is projected to increase every year.
Year |
Demand without Additional Conservation |
Demand with Additional Conservation |
||||||||||
---|---|---|---|---|---|---|---|---|---|---|---|---|
Average Day Demand (mgd) |
Max Day Demand (Mgd) |
Total ERU |
Average Day Demand (Mgd) |
Max Day Demand (Mgd) |
Total ERU |
|||||||
Retail |
PUD |
Lacey1 |
Total |
Retail |
PUD |
Lacey1 |
Total |
|||||
2015 (Plan Yr 1) |
6.4 |
0.5 |
1.7 |
8.6 |
14.9 |
51,560 |
6.3 |
0.5 |
1.7 |
8.5 |
14.8 |
51,183 |
2020 (Plan Yr 6) |
6.8 |
0 |
0 |
6.8 |
13.4 |
41,166 |
6.7 |
0 |
0 |
6.7 |
13.3 |
40,339 |
2034 (Plan Yr 20) |
8.1 |
0 |
0 |
8.1 |
15.2 |
48,782 |
8.0 |
0 |
0 |
8.0 |
15.1 |
48,171 |
2064 (Plan Yr 50) |
10.5 |
0 |
0 |
10.5 |
18.1 |
63,431 |
10.4 |
0 |
0 |
10.4 |
18.0 |
62,628 |
View Figure 3.9 Average Day and Maximum Day Demand Forecast with and without Conservation.
View Figure 3.10 Average Day Demand Forecast Details.
3.4 UNCERTAINTY ANALYSIS OF DEMAND FORECAST
The baseline demand forecast is an estimate of what future demand might be. To understand the uncertainty in the future values, an uncertainty analysis was conducted to define a range of possible future demands relative to the base demand forecast. The analysis takes into consideration uncertainty of demographics, peaking factor and water use factors by using Monte Carlo computational algorithms to determine an overall uncertainty range for demand. Appendix 3.2 is a technical memorandum from HDR Engineering, Inc. presenting the methodology and additional information on the analysis.
The results of the analysis are shown in Figure 3.11 and are compared with the baseline demand forecast presented in Section 3.3. The figure shows the range of Average Day Demands (ADD) and Maximum Day Demands (MDD) for the planning period through 2064. The 50th percentile curve generated by the uncertainty analysis closely matches the baseline demand forecast presented in Section 3.3. The 90 percent confidence interval increases (widens) over time because the uncertainty increases over time. In 2034, the 90 percent confidence interval for ADD ranges from 7.2 to 8.9 Mgd and for MDD ranges from 12.0 to 17.7 Mgd. In 2064, the 90 percent confidence interval for ADD ranges from 8.7 to 14.3 Mgd and for MDD ranges from 13.6 to 24.4 Mgd.
View Figure 3.11 Results of Demand Forecast Uncertainty Analysis.