HYDROLOGY (L6) By Cg. Dk. Malia Pg. Hj. Damit. Geography Department
HYDROLOGY DEFINITION hydrology Hydrological cycle SYSTEM OPENED CLOSED D.BASIN HYDROLOGICAL CYCLE 1.1. DRAINAGE BASIN DEFINITION DIAGRAM FLOW DIAGRAM WATER BALANCE 1.2.STORM HYDROGRAPH
Evapotranspiration Condensation Liquid water turns into a vapour as it absorbed by air. Plants release Water through tiny Holes (stomata) on Underside of leaves. Combined water Loss by evaporation & transpiration. A general term for all Water moving through the atmosphere in liquid or solid form towards the Earth’s surface . HYDROLOGICAL CYCLE : the circular system by which water is transferred Between the oceans and the land masses. As the air cools water vapour turns into tiny droplets of Water called cloud.
A drainage basin is a region of land where water from rain or snow melt drains downhill into a body of water, such as a river , lake , dam , estuary , wetland , sea or ocean .
Interception : first raindrops of a rainfall event will fall on vegetation. Infiltration : Water that reaches ground surface will soak into soil. Overland flow : water moving over the ground. Throughfall : water that drip down leaf to leaf. Percolation : Some water sinks deep into the earth (percolates) through openings in the soil. Stemflow : water that flow down tree thrunks or plant stems. Groundwater : water transfer through permeable rocks from the soil above. Baseflow : water flows from groundwater stores to the stream Throughflow : water moving through the soil. Surface run-off : water that flows over the land surface. TERMS
FLOW DIAGRAM THROUGH A DRAINAGE BASIN TRANSPIRATION INTERCEPTION SURFACE STORAGE SOIL WATER STORAGE EVAPORATION GROUNDWATER STORAGE CHANNEL STORAGE RIVER RUNOFF VEGETATION STORAGE PERCIPITATION inputs storage outputs stemflow infiltration percolation baseflow throughflow Surface flow Channel flow
Interpreting a storm Hydrograph
River discharge : amount of water originated as
precipitation which reaches the channel by surface
run-off, throughflow and baseflow.
Hydrograph: showing the discharge of a river at a
given point over a short period of time.
Storm hydrograph : shows discharge of a river
response to an individual rainfall event.
Approach segment: discharge of a river before the storm (antecendent
flow rate), when storm begins river response is negligible some rain not
fall directly into channel, most fall elsewhere & take time to reach
Rising limb : initial surface run-off occur, and throughflow reach river
rapid increase in discharge occur.
(the steeper the rising limb, faster response to rainfall i.e. water reach
the channel more quickly)
Peak discharge (peak flow) occur when river reaches highest level.
Lag time: the period between maximum precipitation & peak discharge.
(river with shorter lag time had higher peak discharge more prone to
Falling limb/recessing limb : segment of the graph where discharge is
decreasing and river level start to fall. (less steep than rising limb
because throughflow is being released slowly into channel)
Storm flow : is the discharge, both surface and subsurface flow
attributed to a single storm.
Baseflow : very slow respond to a storm, continually releasing ground
water, maintain river flow during periods of low precipitation.
Bankfull discharge occurs when the river’s water level reaches the top
of its channel; any increase in discharge will result in flooding of land.
Porous: e.g. sandstones & chalk (more pores able to fill up and store water)
Pervious: carboniferous limestone (water flow along bedding planes & joints) although rocks impermeable.
(both type of rock allow much infiltration thus little surface run off, low
Granite do not allow water to infiltrate thus produce more surface
FACTORS INFLUENCING STORM HYDROGRAPH: (1) ROCK TYPES:
FACTORS INFLUENCING STORM HYDROGRAPH:
(2) BASIN CHARACTERISTICS :
Basin shape :
Elongated basin: less dramatic graph. (longer lag time & low peak flow)
Circular basin: more dramatic graph. (shorter lag time & high peak flow)
Water takes longer to reach the trunk stream in a large, round basin than in does in a small, narrow one.