Reservoir release plan under a dry-year forecast (profile discipline: water management)
You chair the water-allocation commission for the Sarybulak Reservoir, which supplies a 4,200-hectare irrigation district, a 12 MW hydropower plant, and a downstream wetland protected under national law. It is 1 April. Active storage is 150 million m³, dead storage 15 million m³, and the current level is 68 million m³. The hydrological service gives a median April–September inflow of 45 million m³, but its 80% exceedance estimate is only 28 million m³; evaporation and seepage are estimated at 7 million m³. The ecological minimum is 2.5 m³/s from May through September (153 days). The irrigation cooperative has submitted a request for 62 million m³, and the grid operator invokes a contract requiring at least 15 million m³ through the turbines for summer stability. At median inflow the demands total 110 million m³ against roughly 91 million m³ available. The akimat wants a decision today, before farmers start planting.
1. Compute the water available under the median and the 80% exceedance inflow. Can any of the three demands - ecological, irrigation, hydropower - be met in full? Show your arithmetic.
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Usable storage today is current level minus dead storage: 68 − 15 = 53 million m³.
- Median inflow: 53 + 45 − 7 = 91 million m³.
- 80% exceedance: 53 + 28 − 7 = 74 million m³.
Ecological minimum: 2.5 m³/s × 86,400 s/day × 153 days = 33.05 million m³. Total requested: 33.05 + 62 + 15 = 110.05 million m³.
Deficit: 19.05 million m³ at median, 36.05 million m³ at the dry estimate.
The ecological minimum can be met in both cases, but neither the irrigation request (62) nor the hydropower contract (15) can be met in full. At the dry estimate, after the ecological release only 40.95 million m³ remains for irrigation and hydropower combined - 53% of their 77 million m³ combined request. At median, 57.95 remains, still 25% short. The commission therefore cannot balance all demands; it must allocate a deficit and say so openly.
2. Recommend an allocation and a restriction-trigger rule. Justify the priority order, and state one assumption that could overturn your recommendation.
Read the worked answer
Priority: (1) ecological minimum - a non-discretionary legal obligation, and a shortfall damages a protected wetland with no quick recovery; (2) irrigation - planting decisions are irreversible within weeks and a 4,200-ha district supports livelihoods; (3) hydropower - the contract matters, but a grid operator can buy replacement power or negotiate a penalty more easily than a farmer can replant.
Plan on the 80% exceedance figure, not the median, because the decision is hard to reverse. At 74 million m³ available: release 33.05 for ecology, allocate about 30 to irrigation (48% of the request), and 11 to hydropower; open immediate negotiation on the 4 million m³ contract shortfall. At median inflow, raise irrigation to about 43 and meet the 15 hydropower contract in full.
Trigger rule: if on 1 June storage is below 55 million m³ or the updated seasonal forecast is below 25 million m³, cut irrigation by 20% and hydropower to 8; if storage falls below 45, release ecology plus 10 for irrigation and suspend hydropower. Review monthly.
Assumption: that the ecological minimum is legally fixed for all 153 days. If the regulator allows a temporary 1.5 m³/s drought flow, the allocation changes substantially.