Plan a fair Subak rotation schedule (area-based sharing with optional priority weights)
This calculator helps a Subak association turn a few measurable inputs—canal flow, hours of gate opening, expected losses, and a rotation cycle—into a clear, shareable irrigation plan. It is designed for practical meeting use: enter the canal conditions and list members with their terrace areas, then generate a daily water budget and a rotation-time schedule for the cycle.
What you can do with the results
- Estimate distributable water per day after seepage/evaporation losses and holy-day pauses.
- Allocate water fairly by proportional share: terrace area × optional priority weight.
- Convert volume to time so each member knows how long to open their field gate during the rotation cycle.
- Export a CSV to share in a WhatsApp group, print for a temple meeting, or attach to a request to the irrigation office.
Inputs and assumptions (plain language)
The calculation assumes a single canal flow rate that is available for a fixed number of hours per day. It then reduces that daily volume by: (1) a loss percentage (seepage + evaporation), and (2) a holy-day fraction based on how many days per month irrigation is paused. Finally, it multiplies by the rotation cycle length to get the total water available for the cycle.
Member shares are computed from effective area: (terrace area in are) × (share weight). A weight of 1.0 means a standard share. Use a small bonus (for example 1.1 or 1.2) only when the Subak agrees that a caretaker or duty-holder should receive a slightly larger share.
Formulas used
The calculator uses these steps (units shown):
-
Daily distributable volume (m³/day):
Vday = Q × h × 3600 ÷ 1000 × (1 − L) × (1 − D/30)
where Q is flow (L/s), h is daily water window (hours), L is loss fraction (e.g., 8% → 0.08), and D is holy days per month. - Cycle volume (m³/cycle): Vcycle = Vday × rotationDays
- Member share (dimensionless): share = (area × weight) / Σ(area × weight)
- Rotation time per cycle (hours): hours = (memberCycleVolume × 1000) / (Q × 3600)
Worked example (quick check)
Suppose the canal flow is 40 L/s, the gate is open 14 hours/day, holy-day pauses are 2 days/month, losses are 8%, and the rotation cycle is 7 days. Daily distributable water is: 40 × 14 × 3600 ÷ 1000 ≈ 2016 m³/day before adjustments. After losses and holy days: 2016 × (1 − 0.08) × (1 − 2/30) ≈ 1728 m³/day. Over a 7-day cycle that is about 12,096 m³/cycle.
If a member’s effective area is 20% of the total (after weights), they receive about 0.20 × 1728 ≈ 346 m³/day. Their rotation time per cycle will be about 0.20 × 7 days × 14 hours/day ≈ 19.6 hours (the calculator computes this from volume and flow). Use this kind of back-of-the-envelope check to confirm your inputs are in the right range.
Tips for accurate entries
- Flow rate: if you measure with a bucket, repeat a few times and use an average; canal flow can vary by hour.
- Loss %: lined canals may be closer to 0–5%; earthen canals and hot, windy days can be higher.
- Holy days: confirm the count with the temple calendar; if irrigation is paused only part of a day, enter a fraction (e.g., 0.5).
- Areas: keep all member areas in are (1 are = 100 m²). If you have hectares, multiply by 100.
- Weights: keep weights modest to preserve trust; document the reason for any non-1.0 weight in meeting notes.
Introduction: Why Subak communities benefit from a transparent schedule
Subak associations coordinate irrigation through shared rules, water-temple calendars, and collective maintenance of canals and terraces. A transparent schedule helps members understand why a rotation is set a certain way, reduces conflict when water is scarce, and makes it easier to coordinate labor. It can also support communication with district irrigation offices when communities need repairs, canal lining, or upstream release coordination.
This page is not a replacement for customary law (awig-awig) or temple guidance. Instead, it provides a consistent way to compute volumes and time slots from agreed inputs, so discussions can focus on the assumptions (flow, losses, holy days, and weights) rather than on arithmetic.
Understanding the input fields
Flow rate is the average canal discharge in liters per second. If you only have occasional measurements, use a conservative average for planning. Daily water window is the number of hours per day the gate is open for irrigation. Holy days represent days per month when irrigation is paused for ceremonies or coordinated temple activities. Loss percentage accounts for seepage through bunds and canal banks plus evaporation. Rotation cycle length is how many days the schedule covers before repeating.
Member entries include a name, terrace area in are, and an optional weight. If there is no priority agreement, keep the weight at 1.0. If a weight is used, the calculator marks the row as “Includes priority weight” so it is visible in the schedule.
Limitations and respectful use
The calculator simplifies real hydrology. Actual flows can change hourly with rainfall, upstream diversions, and maintenance conditions. Holy-day timing can vary by temple calendar, and losses can change with season and field condition. Treat the output as a planning estimate and confirm key assumptions in a meeting before adopting a schedule.
If you need to represent communal fields, maintenance duties, or special agreements, use the weight field and record the rationale. The goal is clarity and fairness: everyone should be able to see the inputs, the method, and the resulting rotation times.
How to use this calculator
- Enter Canal flow rate (liters/second) using the unit or time period shown by the field.
- Enter Daily water window (hours) using the unit or time period shown by the field.
- Enter Temple holy days without irrigation (days/month) using the unit or time period shown by the field.
- Run the calculation and compare the output with a second scenario before acting on it.
Arcade Mini-Game: Balinese Subak Irrigation Sharing Calculator Calibration Run
Use this quick arcade run to practice separating useful scenario inputs from common planning mistakes before you rely on the calculator output.
Start the game, then use your pointer or arrow keys to catch useful inputs and avoid bad assumptions.
Water Allocation Schedule
| Member | Area (are) | Share weight | Daily volume (m³) | Rotation time per cycle (hours) | Notes |
|---|
Practical workflow for a Subak meeting
- Measure or agree on a planning flow rate (L/s) and daily water window (hours).
- Confirm holy-day pauses for the month and choose a rotation cycle length (often 7–10 days).
- Read out member areas and confirm any weights (keep them modest and documented).
- Generate the schedule, then export the CSV for sharing and record-keeping.
- If conditions change (drought, repairs, upstream changes), rerun the calculator and compare the new schedule.
For related household planning, you may also find the diaspora remittance fee comparison calculator useful when coordinating maintenance contributions from family members living away from the village.