Appendix A. Water Budget.
Maximum Allowed Landscape Water Budget.
Reference evapotranspiration (ETo) = 49.8 inches/season (Mar – Oct)1
Effective precipitation (EP) = 1.7 gal/sf/season (Mar – Oct)2
Irrigated area = hydrozone area in sq. ft.
|
Water Use Category |
Plant Factor3 |
|---|---|
|
High (including Cool Season Turf and Water Features) |
0.8 |
|
Medium |
0.5 |
|
Low |
0.2 |
|
Very Low/Nonirrigated4 |
0.0 |
|
Irrigation Method |
Default Efficiency |
|---|---|
|
Overhead |
70% |
|
Drip |
90% |
|
Water Feature |
75% |
|
Special Features to Incentivize Healthy Landscapes (% of irrigated landscape) |
Maximum Applied Water Budget (gal/sf/season) |
|---|---|
|
At least 15% |
+3 gal / sf / season |
|
At least 10% |
+2 gal / sf / season |
Special features include:
1. Ecological restoration projects;
2. Bioretention areas;
3. Nonirrigated pervious areas;
4. Storm water conveyance infrastructure (vegetated swales);
5. Graywater applied to the landscape (percent special features based on percentage of living plant material primarily watered with graywater in the overall landscape area);
6. Native vegetation areas;
7. Secondary water irrigation.
1Moller, Alan L., Robert R. Gillies, Utah Climate 2nd Edition, 2008, Utah Climate Center at Utah State University. Note data timeframe is 1889 – 2007.
2Utah Climate 2nd Edition. Precipitation during irrigation season = 6.87 in (Mar – Oct); effective precipitation is equal to 25% of total precipitation during irrigation season.
3Figures based on EPA WaterSense Water Budget tool designations, plus an additional VL/Non-Irrigated category to incentivize VL hydrozone plants
4VL/Non-Irrigated refers to plants that require very little if any supplemental irrigation once the plant has been established (within 2-3 years of planting).
|
Amount of Rainwater Catchment Capacity |
Reduction in Calculated Irrigation Water Need (gallons) |
|---|---|
|
1 x 50-gallon rain barrel |
100 |
|
2 x 50-gallon rain barrel (100 gal) |
200 |
|
101 – 500-gallon cistern |
1,000 |
|
501 – 1,000-gallon cistern |
2,000 |
|
1,001 – 1,500-gallon cistern |
3,000 |
|
1,501 – 2,000-gallon cistern |
3,750 |
|
2,001 – 2,500-gallon cistern |
4,500 |
Sample Hydrozone Tables
Irrigation Water Budget = [(ETo × Plant Factor) – EP] × Irrigated Area ÷ Irrigation Efficiency
Hydrozone |
ETo |
Plant Water |
Plant Factor |
EP |
Irrigation |
Irrigation |
Hydrozone |
Irrigation |
|---|---|---|---|---|---|---|---|---|
|
Zone 1 |
49.8 |
H |
0.8 |
1.7 |
Overhead |
0.7 |
1,000 |
33,945 |
|
Zone 2 |
49.8 |
M |
0.5 |
1.7 |
Drip |
0.9 |
1,000 |
16,059 |
|
Zone 3 |
49.8 |
L |
0.2 |
1.7 |
Drip |
0.9 |
1,000 |
5,718 |
|
TOTAL |
(c) 3,000 |
(d) 55,722 |
Avg. irrigation water need all zones = (d / c) = 18.6 gal/sf/season
Hydrozone |
ETo |
Plant Water |
Plant Factor |
EP |
Irrigation |
Irrigation |
Hydrozone |
Irrigation |
|---|---|---|---|---|---|---|---|---|
|
Zone 1 |
49.8 |
H |
0.8 |
1.7 |
Overhead |
0.7 |
1,500 |
50,917 |
|
Zone 2 |
49.8 |
M |
0.5 |
1.7 |
Drip |
0.9 |
1,500 |
24,089 |
|
Zone 3 |
49.8 |
L |
0.2 |
1.7 |
Drip |
0.9 |
3,000 |
17,153 |
|
TOTAL |
(c) 6,000 |
(d) 92,168 |
Average irrigation water needs = 15.4 gal/sf/season
Hydrozone |
ETo |
Plant Water |
Plant Factor |
EP |
Irrigation |
Irrigation |
Hydrozone |
Irrigation |
|---|---|---|---|---|---|---|---|---|
|
Zone 1 |
49.8 |
H |
0.8 |
1.7 |
Overhead |
0.7 |
1,000 |
33,945 |
|
Zone 2 |
49.8 |
M |
0.5 |
1.7 |
Drip |
0.9 |
1,000 |
16,060 |
|
Zone 3 |
49.8 |
L |
0.2 |
1.7 |
Drip |
0.9 |
1,000 |
5,718 |
|
Zone 4 |
VL |
0 |
1,000 |
0 |
||||
|
TOTAL |
(c) 4,000 |
(d) 55,722 |
Average irrigation water needs = 13.9 gal/sf/season
Hydrozone |
ETo |
Plant Water |
Plant Factor |
EP |
Irrigation |
Irrigation |
Hydrozone |
Irrigation |
|
|---|---|---|---|---|---|---|---|---|---|
|
Zone 1 |
49.8 |
H |
0.8 |
1.7 |
Overhead |
0.7 |
600 |
20,367 |
|
|
Zone 2 |
49.8 |
M |
0.5 |
1.7 |
Drip |
0.9 |
1,500 |
24,089 |
|
|
Zone 3 |
49.8 |
L |
0.2 |
1.7 |
Drip |
0.9 |
3,000 |
17,153 |
|
|
Zone 4 |
49.8 |
VL |
0 |
1.7 |
900 |
0 |
|||
|
Subtotal |
(c) 6,000 |
(d) 61,609 |
|||||||
|
Rainwater Capture |
- |
4,500 |
|||||||
|
TOTAL |
6,000 |
57,109 |
|||||||
Average irrigation water needs w/out cistern = 10.3 gal/sf/season Average
Irrigation water needs w/ cistern = 9.5 gal/sf/season Special Features
|
Special Feature |
Special Feature Response |
|---|---|
|
Total area of Special Features (sq. ft.) |
600 |
|
Total percent of Special Features |
10% |
|
Maximum Applied Water Budget (gal/sf/season) |
+ 2 gal/sf/season |
(Ord. 23-08 § 3, 2023)