Hydrological system

Learning goals:

- hydrological cycle- climate and water availability- catchment area- water balance equation (continuityequation)- runoff coefficient- how to calculate pollutant transport out from the project area

Hydrological cycle

670 mm/year 7/8900 mm/year1/8

129 mm/year

Hydrological cyclecomponents and turnover

time1 week

1 week -10 years

5000 years

8000 years

3000 years

Global water distribution

Atmosphere 0,001%Lakes, rivers, creeks 0,009%

Groundwater, soil 0.615%Ice caps, glaciers 2,04%

Oceans, saltwater lakes 97,31

Atmospheric flow decideswhere water availability is

large or small

Sun energy

Precipitation

Precipitation

No precipitation

No precipitation

Precipitation

Gulf stream suppliesNorthern Europe with 50%

of available heat

Direct sun insolation remaining 50% of the heat

Water balances

P

E

Q

ΔM

WATER FLOWS

Interception losses (evaporation from leafs, etc

Transpiration (from plants)

Soil evaporation Runoff

Soil water Groundwater flow

Water balance equation(or continuity equation ormass balance equation)

PE

QM

ΔM

Storage changes ΔM approx. constant seen over

1 year!

spring spring

ΔM

Q

Lake water, snow, groundwater, soil water

1 year

Example water balancecalculations

Ex 1, For an area the annual precipitation is 1300 mm/year and annual evaporation is 800 mm/year. What is the average runoff?

Ex 2, For the same area precipitation was 700 and evaporation was 500 mm during 6 months. What was runoff if the increase in water storage was 100 mm?

Water balances for different climate types

Boreal forest

Steppe desert

Tropical forest

Catchment area is definedby topographical water

divide

Catchment = rainfall collectingarea upstream a certain point in the water course.

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Examples catchments

Remember: always use the same unit in the water balance equation;

for example mm/year, mm/month, m3/s,

Ex. A 1 ha catchment has received 100 mm rainfall during a month. During the same month runoff was 0.1157 l/s and storagechanges equal to zero. What was the evaporation during the month?

Mean values Q, E, and P(mm/year)

Q E P

Runoff information från SMHI (Swedish Meteorol.

and Hydrol. Institute)

Ex. 2.1, Two rainfall events, just after one another, fall over a catchment. After the first rainfall of 24 mm, a total runoff of 11 mm was observed. The second rainfall is measured to about 14 mm. How large runoff can be

expected after the second rainfall?

P

Q

Rain 1; P1 = 24 mm Q1 = 11 mm Rain 2; P2 = 14 mm Q2 = ?

Ex. 2.2, A 121 ha large lake has an inflow via a river corresponding to 0.425 m3/s. There is also an outflow from the lake via another river that corresponds to 0.368 m3/s. During one month the water level in the lake increases corresponding to 19.7 · 103 m3. During the same month it rained 33 mm. How large was the total evaporation from the lake during this month (1 ha = 10 000 m2)?

Lake Qout

Qin

Ex. 2.3, For a catchment with an area of 20 km2 an average of 732 mm/year of precipitation and total evaporation of 550 mm/year have been observed during a 10-year period. Within the catchment there is an old waste dump and in the outflow water high phosphorous (P) contents have been found 0.25 mg/l P. What is the annual mass transport of phosphorous in the water out from the catchment?

Solution: Put up a water balance for the catchment. That is

P - E - Q = ΔM

A = 20 km2 P = 732 mm/year E = 550 mm/year C = 0.25 mg/l P

P

Q, C

E