Measurements of water balance components have been made for a one-year period on

ID: 1711580 • Letter: M

Question

Measurements of water balance components have been made for a one-year period on a lake with an area of 4.2km^2 with the following results: P=350 mm, Q_si= 2.33 times 10^7 m^3, Q_gi = 2.2 times 10^5 mA3, Q_go = 0.6 times 10^5, and Q_so = 2.10 times 10^7 m^3. The lake-surface elevation, h, at the end of the year was 45 mm lower than at the beginning. What is the water-balance estimate of the lake evaporation for that year in mm? Compare this evaporation estimate to the precipitation estimate. Based on this, what can you infer about the climate in this region? P= Precipitation: Q_si= stream inflow to the watershed: Q_so = stream out flow from the watershed: Q_gi = ground inflow to the watershed: Q_go = groundwater outflow the watershed

Explanation / Answer

ANSWER:

GIVEN DATA:

LAKE AREA=4.2KM^2

P=350MM(AT BEGINING), BUT AT THE END OF YEAR IT REDUCED TO 45MM i.e 350-45=305mm

,Qsi=2.33*10^7m^3,Qgi=2.2*10^5m^3

Qgo=0.6*10^5m^3,Qso=2.10*10^7m^3

IN ORDER TO ESTIMATE EVAPORATION WE NEED TO KNOW WATER BALANCE EQUATION WHICH IS REPRESENTED IN THE FOLLOWING,

EVAPORATION=(S1-S2)+P+(Qsi-Qso)+(Qgi-Qgo)-TR

WHERE

S1=STORAGE AT THE BEGINNING OF TIME INTERVAL

S2=STORAGE AT THE END OF TIME INTERVAL

Qsi=VOLUME OF SURFACE INFLOW ENTERING THE BODY

Qso=VOLUME OF SURFACE OUTFLOW LEAVING THE BODY

Qgi=VOLUME OF GROUNGWATER INFLOW ENTERING THE BODY

Qgo=VOLUME OF GROUNDWATER OUTFLOW LEAVING THE BODY

TR=TRANSPIRATION LOSSES,IF ANY

NOW WE WILL CALCULATE EVAPORATION BASED ON THE ABOVE FORMULAE NEGLECTING THE TRANSPIRATION LOSSES BECAUSE IT IS NOT GIVEN IN THE QUESTION,

EVAPORATION=((0.350*4.2*10^6)-(0.305*4.2*10^6))+350+(2.33*10^7-2.10*10^7)+(2.2*10^5-0.6*10^5)

=2649000.35m^3/4.2*10^6m^2

=0.630m

EVAPORATION=630MM

FROM THE CALCULATIONS WE CAN SAY THAT EVAPORATION ESTIMATE IS GRATER THAN THE PRECIPATION ESTIMATE.

BASED ON THE DATA THE CLIMATE IN THIS REGION COMES UNDER TROPICAL ARID ANDSEMI ARID REGIONS .