DRAINAGE BASIN [GRADE 12 GEOGRAPHY]

THE DRAINAGE BASIN SYSTEM Drainage Basin: the area drained by a river system or stream network. Watershed: High ground separating one drainage basin from another. Stream Network: Individual river channels join together to form a stream network. Interfluves: The ridges of high ground, i.e. spurs, found between individual channel.

DRANAGE BASIN

WATERSHED

INTERFLUVE A minor watershed A watershed within a drainage basin.

CONFLUENCE Where two rivers join

TRIBUTARIES A smaller stream that joins a bigger stream

DISTRIBUTARIES A large river that flows into a number of smaller rivers e.g. at a delta

FACTORS PRODUCING INCREASED RUN-OFF Gradient Steep Vegetation Sparse Rock type Impermeable Soil Not porous, clayey Soul moisture Wet soils Evaporation rate Low e.g. overcast Amount of rainfall Lots Types of rainfall Thunderstorms

FACTORS PRODUCING DECREASED RUN-OFF Gentle Dense Permeable Porous, sandy Dry High Little Soft soaking rain

BASE FLOW

WATERTABLE The upper level of the zone of saturation More or less follows the undulations of the landscape Where it intersects with the surface, rivers, lakes or oases are formed

BASEFLOW

GROUNDWATER ZONES

GROUNDWATER ZONES

GROUNDWATER ZONES (in detail)

WATER SUPPLY Water is one of the most powerful earth carving forces there is. Run off = precipitation – [surface retention + infiltration + evaporation + evapotranspiration + interception]

SHEET/LAMINAR FLOW

TURBULENT FLOW

RIVER SOURCE Where a river rises or begins

RIVER MOUTH

TYPES OF RIVERS Permanent Periodic Episodic Exotic

PERMANENT RIVERS Always has base flow as even the dry season water table is above the river bed Found on the south and east coast of South Africa

PERIODIC RIVERS Flow only in rainy season Dry season water table is below the river bed Found on plateau of South Africa

EPISODIC RIVERS Flo only after a heavy rainfall Wet season water table is also below the river bed River never enjoys base flow Found in dry western parts of South Africa

EXOTIC RIVERS Rise in a high rainfall area where there is plentiful run off and base flow Travel through dry areas where there is very little run off and no base flow Orange and Nile river

OTHER IMPORTANT DEFINITION Interfluve Confluence Water table Tributaries Permeable rock Distributaries Impermeable rock River rises Base flow River mouth Through flow Aquifer Artesian basin