short fart

woke up in time to watch 'zatchbell'. it's the cartoon which used the word 'nincompoop' once. deep. patronizing kfc is always such a pain in the ass. but i do it for the nice food. fatty? i couldn't care less. singapore idol finals is on now, and i've read through the hydrology 1 notes. revise!

hydrology 1

basin hydrological system includes these:
1. precipitation
2. interception storage
3. stem flow, leaf drip, throughfall
4. surface storage
5. overland flow
6. infiltration
7. soil moisture storage
8. throughflow
9. percolation
10. groundwater storage
11. baseflow
12. channel storage
13. channel flow
14. evapotranspiration

precipitation comes in the form of rain, snow, sleet and hail. there are three types of rain: convectional, frontal, relief. interception storage is carried out by plants. it is affected by rainfall intensity and vegetation density.

there are two types of overland flow: horton and saturation. horton overland flow occurs when rate of rainfall exceeds infiltration capacity of soil. saturation overland flow occurs when ground is saturated, such that no rain can enter. there are two types of overland flow: unconcentrated sheet flow and concentrated rilling/gullying.

infiltration refers to the downward movement of water from soil surface into the soil. it is affected seven factors:
1. vegetation
2. rainfall intensity
3. urbanisation
4. compaction
5. terracing
6. soil texture
7. antecedent soil moisture

soil moisture storage involves the concept of capillary water. soil saturation is achieved when pore spaces are completely filled by water. as gravitational water drains away, the soil reaches field capacity. soil moisture withdrawal starts when precipitation is exceeded by potential evapotranspiration. wilting point is reached when plants can no longer exert enough force to absorb soil moisture. this water that the soil retains is known as 'hygroscopic water'.

throughflow refers to the lateral downslope movement of water in the soil. this occurs when vertical downward movement is restricted, which can be due to a clay pan, or more compacted soil below.

groundwater storage involves the concepts of porosity and permeability. soil porosity refers to the presence of voids in the soil particles. soil permeability refers to the allowance of water to move through the soil. the water table is the boundary between unsaturated soil and saturated soil. the zone of aeration is the unsaturated soil. the zone of saturation lies below the water table, and represents groundwater storage.

there are three types of channel flows: perennial, intermittent and ephemeral. these occur depending on whether the stream is under influent or effluent conditions. evapotranspiration is dependent on temperature and relative humidity.

features of a storm hydrograph:
1. lag time
2. rising limb
3. stormflow
4. peak discharge
5. recession limb
6. baseflow

lag time is the time difference between the peak of the rainfall and the peak of the river discharge. it occurs because time is needed for overland flow and throughflow to be generated. lag time is increased if the gauging station is far from the location of the rainstorm. lag time is also increased by intensive rainfall and dense vegetation, since they cause more infiltration to take place. urbanization, basin shape, size and relief also affect lag time.

the height of the peak discharge is affected by the rate of generation of overland flow and throughflow. because if these flows were generated quickly, lag time would be short, and for the same amount of discharge, the peak must be pushed up. as such, urbanization causes high peak discharge because water is not allowed to infiltrate, and overland flow is generated very quickly.

the water table rises as more groundwater is being stored. the water table fluctuates depending on the inputs and outputs into the groundwater storage. the inputs are precipitation recharge, which depends on precipitation and evapotranspiration. the outputs are baseflow, channel flow and spring flow.

the water balance equation: p = q + r +/- s
p is precipitation, q is evapotranspiration, r is runoff, s is storage.

storage can be positive or negative depending on whether evapotranspiration and runoff exceed precipitation. storage affects directly the height of the water table from the soil surface. when describing spatial variations of water balance, compare the water balance of singapore with that of sudan. when describing temporal variations of water balance, use the water balance of britain.

floods occur when river discharge exceed bankfull discharge. they can be caused by excessive rainfall, rapid snowmelt, volcanic action, landslides or dam failures. they are intensified by factors such as basin shape and area, density of vegetation, presence of human construction, and type of soil.

recurrence interval = (n+1)/r

rational runoff method:
peak runoff rate = 0.278 c*i*a
c is the coefficient of rational runoff, i is the rainfall intensity, a is the drainage area.

case studies to use for flood management: singapore, bangladesh, mississippi and china.

primary effects of flood refer to the direct effects caused by the flood, including property damage and loss of lives. secondary effects refer to the disruption of services (gas, water, electricity). tertiary effects refer to the long-term effects such as corruption when dealing with relief supplies and raised insurance rates.

flood effects can be mitigated. levees can be built artificially, as is the case with mississippi. dams can be built, like the three gorges dam. hazard mapping, channelisation, floodways, and controlled floodplain development are other ways to mitigate flood effects.

the management of rivers can lead to conflicts. usually, this is because the river is trans-border. sometimes, it is because the river is a scarce resource. also, different interest groups can produce conflicts too. case studies:
1. three gorges dam
2. aral sea
3. jordan river
4. river nile
5. colorado river

-fin