A drainage basin, or catchment as it is also called, is the part of the land surface that is drained by a single river system. Most precipitation that falls on a drainage basin will eventually reach a main river and flow to the sea. A drainage divide, on either side of which water will flow to separate basins, marks the perimeter of a catchment. The characteristics of such a basin, that is, the size, shape, vegetation cover, soil, and bedrock, determine how fast rainfall reaches a main river and the frequency and severity of flooding.

Diagram represents a typical small drainage basin (catchment) in Newfoundland (idealized). Adapted and colourised by Duleepa Wijayawardhana from a diagram in The Natural Environment of Newfoundland, Past and Present. Edited by Alan G. Macpherson and Joyce Brown Macpherson (St. John's, Newfoundland: Memorial University of Newfoundland, © 1981 MUNCL) 184. with more information (22 kb)

Catchments in Newfoundland and Labrador are fairly typical of areas, with resistant (strong) bedrock, that have been overrun by glaciers. As a result, they have numerous lakes and wetlands and variable slopes. Two types of lakes are common: small, shallow, irregular ponds and larger, deep rock-basin lakes, which may also be called ponds. Western Brook Pond, a large lake in Western Newfoundland, is an example. Small ponds can occupy hollows, either eroded in the bedrock by glacial action, or created by the irregular surface of glacial deposits. Damming due to natural accumulations of glacial, fluvial or marine deposits or even beaver dams may also create ponds.

Rock-basin lakes are usually long and narrow, reflecting the local bedrock characteristics (e.g., faults) and the direction of glacial movement. All the major lakes of the province are of this type. Artificial dams, such as those at Red Indian Lake and Grand Lake on the island's west coast, have enlarged other lakes.

Variable slopes in a drainage basin are most evident along a river's course; steep gradients cause rapids or waterfalls and low gradients form pools or areas of slow currents called steadies. Dramatic waterfalls arise when streams draining into a rock-basin lake fall from a great height as at Western Brook Pond. The energy of a stream falling over a considerable drop can be harnessed to develop hydroelectricity. Churchill Falls in Labrador, Deer Lake in western Newfoundland, and Grand Falls in the centre of the island, have all been used to create hydroelectric power.

The irregular surface produced by glacial activity locally creates poorly drained hollows in a drainage basin; these develop into wetlands (bogs, fens and marshes). Here water logging prevents the decay of dead plant material that as a result accumulates as peat. The southern Avalon Peninsula has so much precipitation that wetlands are very extensive, forming blanket bogs.

© 1998, Joyce Macpherson