How does water move through the drainage basin system?
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- 1. How does water movethrough the drainage basin system?
- 2. Elements of a drainage basin: Inputs Flow / Transfer Storage Output
- 3. Input: major input - precipitation. The type: rain or snow, hail, etc. Factors affecting the amount of water in the system: the intensity, the duration and Frequency of the precipitation
- 4. Flow / transfer: Interception Throughfall Stemflow Overland flow Infiltration Percolation Throughflow Groundwater flow / baseflow Channel flow
- 5. Interception defined as the capture of precipitation by the plant canopy and return to the atmosphere through evaporation or sublimation.* Interception loss: water which is retained by plant surfaces and which is later evaporated away & absorbed by plant
- 6. leaf type increase interception capacity if leaves & twigs are dry wind speed the higher the wind speed the lower the interception capacity - the more frequent the storm events lesser the interception loss temperature, and the humidity of the atmosphere
- 7. Throughfall: the process of precipitation passing through the plant canopy (Yellow lines) Factors affecting: plant leaf and stem density, type of the precipitation, intensity of the precipitation, and duration of the precipitation event.
- 8. Stemflow: is the process that directs precipitation down plant branches and stems (red arrows ). this process causes the ground area around the plants stem to receive additional moisture. The amount of stemflow is determined by leaf shape and stem branch architecture. In general, deciduous trees have more stemflow than coniferous vegetation.
- 9. Infiltration Some of the precipitation seeps into the ground and stored in aquifers then it is transported to streams and lakes by subsurface flow. The amount of infiltration is influenced by: the permeability and moisture content of the soil, the presence of vegetation and the volume and intensity of
- 10. Overland Flow Rills - Water moving over ground in small channels Sheetflow - Water moving over ground across the whole surface Hortonian Overland Flow: Saturated Overland Flow: infiltration excess overland Long period of steady flow rain and water table reach the surface rainfall is greater than infiltration capacity No additional water can E.g. If a soil surface can be infitrated so must infiltrate 30mm/hr but remain on surface precipitation is 40mm/hr, therefore 10mm will be overland flow Common in the temperate Very common in the tropics
- 11. Overland flow
- 12. Rills
- 13. Sheetflow
- 14. A process where water enters the ground vertically through pores Factors affecting infiltration: Intensity & duration of the precipitation Type of soil Vegetation & Land cover Slope of the land Evapotranspiration Soil saturation
- 15. the slow movement of water through compact layers of soil and rocks Factors affecting percolation: Precipitation Relief steeper the gradient the less water will be percolated Flora & fauna animal tunnels & burrow - root system of direct movement of water in the soil Rock structure / composition Porous rock sandstone Permeable rock - limestone
- 16. Water transfers laterally in the aquifers If the water table reaches the surface it means ground is saturated.(a) infiltration to deep groundwater,(e) overland flow to (g)(g) temporary ponds(f) deep groundwater flow.
- 17. Channel flow Water transfers to channel through 3 processes: Surface run-off Throughflow Groundwater flow /baseflow
- 18. Rainfall Vegetation and land use Climate Shape Conditions in drainage basin Size and shape of the river basin Soil type and depth Bedrock
- 19. Groundwater Storage Interception Storage Aeration Zone Storage Depression Storage Surface Storage
- 20. Process of percolation produces groundwater storage Water collected above the impermeable layer Or it may fill all the pores spaces, creating a zone of saturation Above the impermeable layer, there are 3 zones: An unsaturated zone A saturated zone An intermediate zone
- 21. Soil pores are mostly filled with microchannels so water can move as percolation and throughflow Biological activity with plant roots, soil flora and fauna create microchannels
- 22. Water accumulates all the soil pores are full of water Baseflow / groundwater occurs No biological activity
- 23. Zone between the unsaturated and saturated zones Changing patterns of precipitation and EVT throughout the year gives a layer which is alternatively saturated and unsaturated Interflow occurs
- 24. 18 Infiltration rate 16 Rainwater which is not infiltrated will become 14 surface run-off / overlandInfiltration Rate flow 12 10 8 6 4 2 0 1 2 3 4 5 6 Hours from the start of rainfall
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