Design and Modeling of an Adaptively Controlled Rainwater Harvesting System
Abstract
:1. Introduction
2. Materials and Methods
2.1. Inputs
2.1.1. Precipitation
- Total Precipitation: 1172.7 cm;
- Number of Precipitation Events: 652;
- Largest Precipitation Event: 19.2 cm over 77 h (beginning on 12 October 2005).
2.1.2. Subcatchments
2.1.3. Infiltration
2.1.4. Evapotranspiration
2.1.5. Cistern Geometry
2.1.6. Raingarden Geometry
2.1.7. Irrigation Area
2.1.8. Irrigation Demand and Delivery
3. Results
3.1. Model Scenarios
- The Base Scenario (i.e., existing conditions) was developed to simulate unmanaged runoff to the site outfall to the combined sewer system as a point of reference to compare the performance of the other model scenarios. All subcatchment runoff (i.e., roof, driveway, lawn) was routed directly to the site outfall.
- The Timed Scenario was developed to simulate conventional timer based operation of a rainwater harvesting system by irrigating the grassed irrigation area from harvested rainwater stored in the cistern at a pre-determined time each day (“irrigation use”). It is expected that this scenario will result in the most irrigation use of all scenarios.
- The Moisture Scenario was developed to simulate “smarter” irrigation by maintaining optimal soil moisture within the root zone of the grassed irrigation area (i.e., the range between the soil’s AD and FC). It is expected that irrigation will be required less frequently during months where PET is low (e.g., May, October) and immediately after precipitation events and that this scenario will result in less irrigation use than that of the Timed Scenario.
- The Active Scenario was developed to pair moisture based irrigation with forecast-based logic and adaptive control of the cistern’s discharge valve. The purpose of this simulation is to demonstrate the operation and benefits of a completely automated CMAC system. Logic rules were designed to minimize overflow from the cistern to the raingarden during periods of active rainfall (“wet weather”) and to minimize irrigation use. Overflow from the cistern is minimized as follows: When the predicted runoff volume from the roof subcatchment (due to an approaching rainfall event) exceeds the available storage volume in the cistern, stored water is released to the raingarden through the controlled discharge valve before rainfall begins (during dry weather) to maximize storage capacity within the cistern for the approaching rainfall event.
3.2. Event-Specific Results
- Timed Scenario: The cistern’s water level decreased daily from scheduled irrigation; however, the raingarden overflowed to the site outfall during both rainfall events despite beginning each event empty. The Timed Scenario used significantly more harvested rainwater for irrigation than that of the Moisture and Active Scenarios (Figure 3).
- Moisture Scenario: The cistern’s water level decreased once on 17 June 2013 from moisture based irrigation and overflowed to the raingarden during both rainfall events. The Moisture Scenario resulted in the most cumulative site overflow because water in the cistern was only reduced once for irrigation (Figure 4).
- Active Scenario: The cistern’s water level was effectively managed from 9 June 2013 through 18 June 2013. The cistern was drained in advance of both rainfall events to accommodate expected roof runoff volume; the raingarden did not overflow to the site outfall as a result of either rain event. Additionally, irrigation only occurred once on 17 June 2013 (Figure 5).
3.3. Long-Term Runoff Analysis
3.3.1. Cistern Performance
3.3.2. Site Performance
3.4. Irrigation and Vegetation Health Analysis
4. Discussion
5. Conclusions
Acknowledgments
Author Contributions
Conflicts of Interest
References
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Month | PET (cm/Month) |
---|---|
January | 1.14 |
February | 1.68 |
March | 3.51 |
April | 5.89 |
May | 9.09 |
June | 10.21 |
July | 11.20 |
August | 9.60 |
September | 6.58 |
October | 4.04 |
November | 1.91 |
December | 1.14 |
Condition | Volumetric Water Content 1 | Model Process 2 |
---|---|---|
Saturation | 46% | PET, Runoff, Infiltration |
Field Capacity | 30% | PET, Infiltration |
Permanent Wilt Point | 10% | PET |
Scenario | Variable | Condition | Action |
---|---|---|---|
---Irrigation Rules--- | |||
Timed | Month | May through October 1 | Irrigate if all conditions met |
Cistern Depth | >30.5 cm2 | ||
Time | 6 am to 10 am | ||
Moisture | Month | May through October | Irrigate if all conditions met |
Cistern Depth | >30.5 cm | ||
Time | 6 am to 10 am | ||
Soil Moisture | <Allowable Depletion | ||
Active | Month | May through October | Irrigate if all conditions met |
Cistern Depth | >30.5 cm | ||
Time | 6 am to 10 am | ||
Soil Moisture | <Allowable Depletion | ||
24-h Rainfall Forecast 3,4 | None in forecast | ||
---Discharge Valve Control Rules--- | |||
Timed | Not Applicable | Not Applicable | Not Applicable |
Moisture | Not Applicable | Not Applicable | Not Applicable |
Active | Month | May through October | Drain cistern to accommodate predicted runoff volume if all conditions are met |
24-h Pred. Runoff Volume 5 | >Available Cistern Storage Volume | ||
6-h Rainfall Forecast 6 | None in forecast | ||
Past 12-h of Rainfall 7 | <0.25 cm |
Variable | Base Scenario | Timed Scenario | Moisture Scenario | Active Scenario |
---|---|---|---|---|
Roof Runoff (m3) | 172 | 172 | 172 | 172 |
Cistern Overflow (m3) | - | 105 | 148 | 43 |
Controlled Discharge (m3) | - | 0 | 0 | 111 |
Cistern Capture (%) | - | 41.3 | 14.8 | 76.6 |
Variable | Base Scenario | Timed Scenario | Moisture Scenario | Active Scenario |
---|---|---|---|---|
Total Runoff 1 (m3) | 550 | 550 | 550 | 550 |
Site Overflow (m3) | 550 | 208 | 222 | 178 |
Site Capture (%) | - | 64.6 | 61.9 | 69.8 |
Variable | Timed Scenario | Moisture Scenario | Active Scenario |
---|---|---|---|
Cistern Storage (% Full) | 74 | 90 | 82 |
Irrigation Use (m3) | 59 | 13 | 11 |
Cistern Empty (days) | 9.2 | 3.4 | 6.4 |
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Roman, D.; Braga, A.; Shetty, N.; Culligan, P. Design and Modeling of an Adaptively Controlled Rainwater Harvesting System. Water 2017, 9, 974. https://doi.org/10.3390/w9120974
Roman D, Braga A, Shetty N, Culligan P. Design and Modeling of an Adaptively Controlled Rainwater Harvesting System. Water. 2017; 9(12):974. https://doi.org/10.3390/w9120974
Chicago/Turabian StyleRoman, David, Andrea Braga, Nandan Shetty, and Patricia Culligan. 2017. "Design and Modeling of an Adaptively Controlled Rainwater Harvesting System" Water 9, no. 12: 974. https://doi.org/10.3390/w9120974
APA StyleRoman, D., Braga, A., Shetty, N., & Culligan, P. (2017). Design and Modeling of an Adaptively Controlled Rainwater Harvesting System. Water, 9(12), 974. https://doi.org/10.3390/w9120974