The Zarafshan in sixteen blocks a first model of the oasis

Before you play: what this model shows, and why

What you see. A simplified Zarafshan, from the Ravatkhoja headworks down to below Navoi, for one water year from October to September, month by month. Upstream: the headworks with the transfers to Jizzakh and Kashkadarya, the Samarkand canals (the upper fields) and the cities. Then the weir that fills the Kattakurgan reservoir in winter. Below it: the lower headworks with the thermal power plant and the canals of Kattakurgan and Navoi (the lower fields). At the end, the river that must still flow for nature and for the users downstream. Water drained from the fields comes back months later. Every block is a TaqSim block of one of six kinds; the same kinds build the full basin model.

What you can change. Three levers, each a decision a basin manager really takes. The river reserve: the share of each month's flow that both headworks must leave in the river. The fill share: how much of the winter water the weir sends into the reservoir. The release share: how much of what is missing below the reservoir in summer is released from it.

What you watch. Four results: upper fields supplied, lower fields supplied, downstream needs met (months out of twelve), and water left in the reservoir on 30 September, against the 170 Mm³ it held on 1 October. Five worlds to run them in: a dry, a mean and a wet year from the record, and the mean year as the climate models project it for 2041–2070 and 2071–2099 (see the provenance notes below for the source).

Why this system is interesting. In the mean and wet years almost everyone can be served. In the dry year about a quarter less water arrives, and the order of service becomes visible: the upper fields are served first, and no lever changes that; every cubic metre kept for the river or for next year is taken from the lower fields. No plan gives the lower fields 40 % of their need, meets the downstream needs in all twelve months and keeps 170 Mm³ at the same time. In the future worlds the year brings as much water as today, but earlier: more in April and May, less in July and August, when the crops need most. That hurts first whoever has no storage, the upper canals, while the reservoir shields the lower fields. The game lets you find all this out by trying, which is the point.

What to try. Follow the tasks on the right. First find the blocks and play a year. Then, in the dry year: meet the downstream needs in every month and see who pays; give the lower fields 40 % and see what breaks; keep 170 Mm³ in store and see what the reservoir costs the fields. Open the Trade-off explorer: among all lever settings, which plans does no other plan beat, and what does each cost on the other axes? Finally switch to the 2071–2099 world and play the year.

What a water manager takes away. In a dry year, allocation is a choice among losers, not a technical optimum; the levers decide who loses. The order of service at the headworks matters more than any single lever. Keeping water for next year has a price this year, and the model makes it visible. Plans that no other plan beats are many, and choosing among them is a decision the model informs but cannot make. And when the water comes at the wrong time, storage is the adaptation.

The river as blocks

Whole year

Scroll sideways to see the whole river →

Water flows from left to right; the arrowheads show the direction. A dashed arrow that ends in the open is water that leaves to the air: evaporation, and ET (evapotranspiration), the water the crops use. Numbers on the lines are Mm³ (million m³) that flowed in the year or month shown; the numbers at the reservoir and at the two Drainage blocks are Mm³ stored (in the year view: on 1 October and on 30 September). The line width shows the flow in m³/s. Dashed lines lead to and from the reservoir. A thin dotted line carries no water. The column in the Reservoir box shows its storage. Each Drainage block is the ground under the fields above it: the water that drains from them returns to the river months later. Each user's box says what it needs. At a canal, “a of b” means: the canal took a of the b it needs, including what is lost and what drains away. The river line gets wider where the power plant and the Drainage block give water back. The numbers under Inflow and River end are what enters and what leaves the model. ✓ supplied, ✕ not fully supplied. Click a block to see what kind of TaqSim block it is and what it does.