Block 2: Surface Water + Watersheds + Water Budgets

What today is about

Block 1 named the reservoirs. Today: how water moves through them in a specific physical basin.

The unit of analysis for surface water is the watershed (drainage basin): every drop of rain that falls within its boundary ends up in the same outlet stream, river, or coastline. Watersheds nest inside watersheds: the Cooum watershed sits inside the Bay of Bengal catchment; a single neighborhood's stormwater drainage sits inside the Cooum's. The watershed is the right unit because it's the unit politics has to wrestle with: you can't draw a political border across a watershed without making someone upstream or downstream pay. The Cauvery dispute is a watershed politics problem: the basin crosses four states and one union territory.

Once you have the watershed boundary, you can write a water budget. Inputs (precipitation, inflow from upstream, recharge from below) on one side. Outputs (evapotranspiration, withdrawals for irrigation / cities / industry, outflow downstream) on the other. Storage (in lakes, soil moisture, snowpack) in the middle. The balance over a given period (a month, a monsoon, a year) tells you whether the basin is in deficit (drawing storage down), balance (steady state), or surplus (storage rising). Chennai's Cooum and Adyar basins (from U2 Block 3) are typically in deficit through the dry months and briefly in surplus during monsoon peaks. The Cauvery basin as a whole has trended toward annual deficit for the better part of two decades.

Why this matters for the Position Paper: a Tamil Nadu delta farmer's argument and a Karnataka upstream farmer's argument disagree most sharply on which inputs and outputs count in the basin's budget. Budgets aren't neutral. The framing is part of the argument.