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Drainage Basin(1)

Drainage Basin(1). What is drainage basin? - An area of land drained by a river and its tributaries (river system). - Its boundary is marked by a watershed (highland surrounding the lowland). Drainage Basin(2). Drainage basin as an open system:

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Drainage Basin(1)

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  1. Drainage Basin(1) • What is drainage basin? - An area of land drained by a river and its tributaries (river system). - Its boundary is marked by a watershed (highland surrounding the lowland).

  2. Drainage Basin(2) • Drainage basin as an open system: 1. Flows of energy and matter in and out in the drainage basin. 2. Major components: a. Inputs: - climatic inputs: precipitation and temp. - geological input: rocks - relief input - vegetation cover

  3. Drainage Basin(3) 2. b. Processes and storage of energy and matter: - Denudation (weathering, mass wasting, transportation, erosion and deposition) - Storage of matter (water, load) and energy in river channels - Transfer of matter and energy through a number of processes (infiltration, percolation, base flow, seepage, etc.)

  4. Drainage Basin(4) 2. c. Outputs: - River discharge entering the sea or returning to the atmosphere - Sediments finally deposited in the sea - River landforms along the course

  5. Drainage Basin(5) 2. d. Linkages to other subsystems: - Weathering subsystem - Slope subsystem - Channel subsystem

  6. Drainage Basin(6) • Analysis of drainage network: quantity approach a. Stream order: - Within a drainage basin, a constant geometrical relationship exists between the occurrence of one stream order in the hierarchy and the number of streams in the next highest order. - The number of stream decreases with the stream order. - A drainage basin is described in terms of the highest order stream within.

  7. Drainage Basin(7) 3. b. Stream density : - the average length of stream channel per unit area of drainage basin, i.e. km/ sq. km. - Stream density = channel length Area

  8. Drainage Basin(8) 4. Factors controlling drainage density: a. Climatic factors: - precipitation: annual amount, distribution, variability - temperature affects evaporation b. Geological factors: permeability of rocks c. Soil : permeability of soil d. Topography e. Vegetation cover: infiltration of rainfall f. Human activities: urbanization, farming, transportation

  9. Drainage Basin(9) 5. Bifurcation ratio: a. It shows the relationship between the number of streams of one order of magnitude with those of the next higher order. b. Bifurcation ratio = No. of first order streams No. of second order streams

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