💧 Watershed Water-Balance Simulator
Drag the controls and watch a design-storm partition into surface runoff, evapotranspiration, soil storage and groundwater recharge in real time. Then switch to Design Challenge mode and compete to hit hydrological targets. Built for hydrology & water-resources students.
Surface runoff
Evapotransp.
GW recharge
Δ Soil store
Runoff ET Recharge Soil storage
The model behind the game
Surface runoff is computed with the USDA-SCS Curve Number method:
S = 25400/CN − 254 (mm) • Ia = 0.2 S • Q = (P − Ia)² / (P − Ia + S) for P > Ia, else Q = 0
Infiltration F = P − Q feeds a single-bucket soil store (field capacity 150 mm). Actual ET is drawn from the store up to the PET limit; any water above field capacity becomes groundwater recharge. The four outputs close the balance: P = Q + ET + Recharge + ΔSoil storage. CN is looked up from the land-cover × soil-group table and nudged upward for steeper slopes and wetter antecedent conditions (AMC). Values are illustrative teaching approximations, not a substitute for a calibrated model such as SWAT or HEC-HMS.