Rain falling on a watershed has several possible paths. Some infiltrates and recharges shallow or deeper groundwater. Some is held in soils, tanks and wetlands. The remainder travels as overland flow into small channels and eventually a main river. A heavy shower on dry compacted ground can produce a fast local flood while adding little useful groundwater. Conversely, moderate rain spread over weeks may recharge aquifers and support crops. This is why a single annual rainfall total explains neither flood nor drought well.
The headwater area controls much of the downstream response. For Godavari and Krishna, large portions of the catchment lie outside Andhra Pradesh. A flood at a lower AP station may reflect rain and releases far upstream. For short north-coast streams, a hill storm can move from catchment to settlement quickly. On a map, mark the watershed boundary in pencil, then draw each river inside its own basin. Never infer a basin from the name of the modern district through which only its lower reach passes.
A confluence is where channels join; a distributary junction is where one channel splits. Reservoir operations may alter the shape and timing of a flood hydrograph, but they do not erase the underlying basin. Sand mining, encroachment and blocked floodplains can also alter local flow. For a police response question, the useful geographic sequence is upstream trigger, channel route, bridge or settlement exposure, and downstream warning.
Worked map reasoning
A watershed line divides two neighbouring valleys. Rain landing on either side normally drains to different rivers, even where the valleys lie in one district. A canal can cross that divide; the natural basin does not move. In an MCQ, ask whether the sentence describes rainfall drainage, project command or administrative location. The same village can be described differently under these three maps without contradiction.
Active recall: close the book, place the named river or region on a blank map, and explain one likely exam confusion in your own words.