Almar River: Reservoir or Demand Management in a Drought Year?
The Almar River rises in a landlocked upland country and crosses into Beran, a low-income coastal state, before reaching a delta of 1.8 million people. A 2016 treaty allocates 60% of annual flow to Beran and 40% upstream, but in 2024 upstream storage and irrigation expanded and actual dry-season flow at the border fell to 72% of the 1990–2010 mean. Beran's irrigation district of 94,000 ha depends on the river; rice yields fell 11% in 2024. Groundwater abstraction in the delta has risen 6% a year and the water table is dropping 1.8 m a year; salinity intrusion reaches 34 km upstream at low flow. The national water authority proposes a $340 million new reservoir on a tributary to 'secure supply', while the irrigation board wants canal lining and metered pricing. Farmers pay a flat fee of $12 per season regardless of volume. The delta's shrimp farmers, who earn three times rice farmers per hectare, want more brackish water.
1. Assess whether the new reservoir is the best response, using supply-side and demand-side reasoning.
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The reservoir is a supply-side answer to a demand and allocation problem. It would add storage, but in a hot basin evaporation from a large surface may be 2–3 m a year, and sedimentation reduces yield over decades. Construction takes 5–7 years and $340M, during which the aquifer continues to fall 1.8 m a year and salinity reaches 34 km upstream. It also does not resolve the treaty: a unilateral tributary reservoir may capture water that Beran counts on, inviting retaliation or arbitration.
Demand-side options are cheaper and faster. Canal lining can cut seepage by roughly 20–30%; metering and a block tariff can reduce over-irrigation; laser levelling and alternate wetting and drying can raise water productivity. These can be implemented in one to three seasons and reduce the need for new storage. The flat $12 fee means the marginal price of water is zero, so farmers have no incentive to line canals or adopt efficient practice.
But demand management alone is not enough. The delta needs a freshwater pulse to hold back salinity, and groundwater recharge must be increased, not just abstraction reduced. Managed aquifer recharge in wet years, with abstraction caps, addresses both. The reservoir could be part of a portfolio if it is operated for environmental flows and if the treaty allocation is renegotiated transparently.
Equity matters. Shrimp farmers earn three times rice farmers per hectare and want more brackish water; rice farmers face an 11% yield fall. A tariff that prices water without protecting smallholders would transfer income to larger farms. The judgement: reject the reservoir as the primary response, fund lining, metering and recharge first, and make any reservoir conditional on a joint basin study and environmental flow agreement.
2. Explain how the flat $12 per season fee distorts water allocation, and outline a tariff design that would not harm poor farmers.
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The flat fee makes water free at the margin. A farmer paying $12 per season faces zero additional cost for the next cubic metre, so the rational response is to expand irrigated area, grow water-intensive rice, and delay canal maintenance. The fee covers none of the delivery cost, so the irrigation board has no revenue for lining. Because the fee is per season, not per hectare or volume, it also subsidises large farmers more in absolute terms.
A metered tariff needs three design features. First, measure at the tertiary canal outlet rather than every field, to keep transaction costs low. Second, use a rising block: a free or very cheap lifeline volume for smallholders, then increasing prices for volume above crop requirement. Third, protect tenants and sharecroppers, who may not control the pump but would pay the bill.
Revenue use. Ring-fence revenue for canal lining and monitoring so farmers see a service return. A sudden volumetric charge on poor farmers would cause protest and non-payment; a phased tariff with a public register of allocations is more feasible.
Groundwater must be priced separately. The tariff covers surface water, but the water table is falling 1.8 m a year because of unlicensed wells. A surface tariff without groundwater regulation will push farmers to pump more. The judgement is that metering is necessary but not sufficient: it must be paired with well registration and a recharge programme.
3. Identify two data gaps and explain how filling each would change the decision.
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Data gap 1: actual consumptive use and seepage. The authority knows allocation, not use. Remote sensing of evapotranspiration, combined with flow gauging at canal head, midpoint and tail, would show whether lining would save 20% or 5%. If seepage is small, lining is poor value and the reservoir case weakens; if large, lining becomes the first investment.
Data gap 2: groundwater recharge and saline intrusion rates. The 1.8 m/yr decline is a net figure. Without recharge estimates and monitoring wells, the authority cannot know whether abstraction caps would stabilise the aquifer in five years or fifty. Salinity monitoring at 34 km upstream is a snapshot; a longitudinal survey at spring and neap tides would show whether the wedge is advancing.
A third gap is upstream operating data. The treaty says 60/40, but actual dry-season flow is 72% of the 1990–2010 mean. Without reservoir release records, Beran cannot distinguish drought from non-compliance. That changes the decision: if the shortfall is hydrological, a new reservoir may help; if it is upstream abstraction, the remedy is negotiation and monitoring.
How this changes the decision. If seepage is high and recharge is low, invest in lining plus recharge and defer the reservoir. If seepage is low and upstream releases are the problem, the reservoir is a hedge but diplomacy is cheaper. The judgement should be contingent on these data, not on the reservoir's symbolic value.