Liquidity,
rooted in nature

A dam does not make water. It holds back what the catchment sends down and releases it on a schedule, which is why the number everyone watches is a level.

1 Live storageThe water above the intakes: the part that can actually be drawn. It is reported as a surface elevation and turned into a volume through a curve of area against height, surveyed for this reservoir alone. 2 The crestThe top of the wall, and the line the lake is never allowed past. The gap you can see between the surface and the parapet is freeboard, kept clear so a flood has somewhere to go. 3 The gatesThe spillway. When inflow beats what the outlets can pass, the surplus goes over here and is lost downstream. Gates running is a sign of a full reservoir, not of plenty. 4 The plunge poolWhere the sheets land. The basin is cut deep on purpose, so the energy in the falling water is spent turning water over instead of on the foot of the wall. 5 Stilling basinA second, smaller step that takes the last of the turbulence out of the flow before the river is handed back to its own bed.

1. 1

   Live storage

   The water above the intakes. The only part that can actually be used.

2. 2

   Dead storage

   The bottom, below the lowest outlet. In the lake, but out of reach.

3. 3

   Penstock

   Head becomes power, so a low reservoir is worth less per cubic metre.

4. 4

   Spillway

   The relief valve. Running means full, not plentiful.

A level is a balance, not a forecast: what the catchment sends down, minus what is released, minus what the sun takes back. Hydropad writes one reserve's ticker into the token and keeps its published figures beside it. Price comes from the curve alone. The mechanics in full →