Watershed Delineation & Groundwater Baseflow

Rainfall & Soil

Rainfall intensity 50%

Soil infiltration capacity 40%

Baseflow recession k 0.15 / s

Live Readouts

Watersheds found

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Groundwater storage

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Quick flowBaseflow

Total streamflow

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Baseflow fraction

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How it works

Every terrain cell drains toward its steepest downhill neighbour (the D8 rule, used by real GIS hydrology tools):

slope(i→j) = (h_i − h_j) / dist(i,j)
downstream(i) = argmax over 8 neighbours j of slope(i→j)

Following every cell's chain of steepest descent to where it leaves the grid (or hits a pit) traces out a tree rooted at that outlet. Reversing those links and flood-filling upstream from each outlet delineates its watershed — every cell whose rain eventually reaches that point — shown here as a distinct colour. The alternate view accumulates 1 unit of rain per upstream cell along the same tree to show flow accumulation (brighter = more upstream area, i.e. where a real stream channel would form).

Not all rain runs off the surface. A fraction infiltrates into the soil and recharges a groundwater store, modelled as a classic linear reservoir:

dS/dt = I(t) − k·S(t)
Q_baseflow(t) = k·S(t)
Q_total(t) = Q_quickflow(t) + Q_baseflow(t)

where S is groundwater storage, I is the infiltration input rate, and k is the recession constant — this is the same hydrograph-separation model used to split a real river's flow into "quick" storm response and slow, sustained baseflow fed by the aquifer.

Rainfall intensity — how fast drops fall and how much water each infiltration event adds to storage.
Soil infiltration capacity — the probability a drop soaks in (blue→green particles) rather than running off along the flow-direction tree (blue drops tracing the terrain).
Baseflow recession k — how quickly stored groundwater releases back out as baseflow; higher k drains the aquifer faster but keeps less water in reserve.

Surface runoff Infiltrating drop Water table

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Watershed Delineation & Groundwater Baseflow Simulator