ontinues.
Precipitation
Precipitation
transpiration
Interception
Detention
Infiltration storage Depression
storage Overland Evaporation
Percolation flow
Capillary rise
Groundwater Table Subsurface flow
Sea
Groundwater storage
Channel
storage
Fig 1.1 The Hydrologic Cycle
The Water Balance Concept
Air Moisture Above Land
Transpiration Precipitation Evaporation
Interception
Depression/Detention
Overland Flow
Infiltration
Subsurface Channel Storage
Moisture Storage flow
Capillary Rise Percolation Seepage
Influent (+), Surface
Effluent (-) Runoff
Groundwater Storage
Symbols
Ocean Storage
Storage
Process
N
O1
O2
The catchment area increases as the outlet is moved downstream. For outlet O 1 the catchment boundary is O1MNPO1
and for outlet O2 the boundary is O2MNPO2.
Hall (1996)
Clear Lake has a surface area of 708 000 m2. For the month of March, this lake had an inflow of 1.5
m3/sec and an outflow of 1.25 m3/sec. A storage change of +708 000 m3 was recorded. If the total
depth of rainfall recorded at the local raingauge was 225 mm for the month, estimate the combined
evaporation and percolation losses from the lake. State any assumptions that you make in your
calculations.
P E
Qi
Q
Gi o
Pe G
rc o
P + Qi – (E+Perc) – Qo = V(f)- V(i)
(E+Perc) =P + Qi– Qo - [V(f)- V(i)]
m
P 225mm( )(708000m 2 ) 159300m 3 / mos
1000mm
m3 s day
Qi 1.5 (86400 )(31 ) 4017600m3 / mos
s day mos
m3 s day
Qo 1.25 (86400 )(31 ) 3348000m3 / mos
s day mos
S
V ( f ) V (i ) 708000m 3 / mos
t
Therefore : ( E Perc ) 159300 4017600 3348000 708000
m3
( E Perc ) 120900
mo
or (E+Perc)=171 mm over the lake.
