6 Groundwater management

Question 1

Evapotranspiration

Evaporation

Answer 1

function of solar radiation, temperature, humidity, wind velocity

(1) potential evaporation
(2) actual (real) evaporation

Question 2

Evapotranspiration

Transpiration

Answer 2

plant water consumption (cooling), only during growing period

•birch tree 60-70 l/d, beech tree (100 years old): 400 l/d, sun flower 1 l/d

Question 3

Evapotranspiration

Interception

Answer 3

at plant surfaces (leaves, branches) followed by evaporation

• evergreen trees (conifer): 30-40% of precipitation throughout the year,
• decidious trees: 10-20% during winter, 20-30% (or more) during summer
• agricultural crops: 10-25 % during growing period

Question 4

Potential evapotranspiration

Answer 4

theoretical value asssuming unlimited water available

ETpotduring winter often = real evapotranspiration,
ETpotduring summer often > real evapotranspiration

Question 5

Empirical methods to calculate Potential Evapotranspiration

Answer 5

HAUDE,

SCHENDEL,

THORNTHWAITE;

PENMAN,

IVANOV

Question 6

Real evapotranspiration

Answer 6

possible evapotranspiration, limited by available water quantity

during winter often ETpot = ETreell

during summer often ETpot > ETreell

Question 7

Measurement of climate parameters - evaporation

Answer 7

HELLMANN cup

PENMAN pan

Pottomer

Question 8

Groundwater recharge

[mm/a]
or
[l/s*km²]

Answer 8

GwR = P –ET -Ao

Important methods:

• from catchment water balance
• from soil water balance
• base flow measurements
• chloride balance
• lysimeter
• “peak shift“ (tracer, e.g. isotopes)
• age stratification…

Question 9

Chloride balance

Answer 9

GwR= P * (Clrain / Clgroundwater)

Assumption: chlorides is conservative tracer

Correction for surface run-off and dry deposition may be necessary

Does not work (well) if additional chloride sources are present:

• sea spray
• dry deposition (salt dust in arid regions)
• air and ground water contamination

Question 10

Direct measurement of groundwater recharge: Lysimeter

Answer 10

Big sample of soil which act like normal soil. when rain event happens, water will flow into the lysimeter and out to the collecting bucket under the sample

Question 11

Land use and gw recharge

Answer 11

Bare soil gives actually much higher groundwater recharge in terms of quantity compared to heavily vegetated surfaces such as forest because big trees intercept much rainfall water and contribute to high evapotranspiration. But cutting down trees is always a bad idea in terms of erosion, CO2 storage, water quality, etc.

Question 12

Sustainable use of groundwater

Answer 12

Sustainability: extraction of groundwater should be smaller (or at least equal) to average (long-term) groundwater recharge
→avoid “groundwater mining“

Question 13

Managing groundwater use

Answer 13

-water demand (min, max, mean)
How much water do I want/need?

-(ground) water availability
Can system cover water demand on a sustainable basis?

-environmental impact
(e.g. on gw dependent ecosystems)
How does the extraction affect nature?

Question 14

Water demand

Answer 14

Population & per capita demand

Population growth (prognosis)

Network coverage

Industry and commerce

Future effects of water savings?

Future effects of increase of GDP?

Question 15

Minimum –Maximum demand:

Answer 15

• daily fluctuations
• work days/weekends
• holidays and vacation
• seasons
• special occasions

Question 16

Availability of groundwater

Answer 16

• groundwater recharge rate
• catchment area (equipotential map)
• boundary condition (e.g. rivers)
• other users

Question 17

Groundwater towards its environmental impact

Answer 17

• groundwater-dependent ecosystems
• subsidence
• land requirements (pipelines)
• impacts on water quality

Question 18

Bank filtration definition

Answer 18

an enrichment of groundwater by infiltration water from rivers

Question 19

Bank filtration Advantages

Answer 19

# compared to direct intake from river:
- filtration of microoganisms & particles, biological degradation of contaminants in aquifer

compared to groundwater:

• high yield (if aquifer permeable)
• often soft water (low carbonate)

Question 20

Bank filtration Disadvantages

Answer 20

• inundation by high waters: well heads need to be pressure tight
• pumping rate may be restricted at low river water
• danger of contamination through accidents

Question 21

Artificial recharge of ground water

Answer 21

Pumping the water from the river and from there water goes to infiltration pond then infiltrates into the subsurface and then flows to the well