Transcript Why self-monitoring by groundwater users

CD-Rainfall method
A quick method to make a
groundwater balance
CD-Rainfall method
The Cumulative Departure-Rainfall (CD-Rainfall)
method is a method to rapidly understand
groundwater conditions.
It only requires:


Periodic rainfall data
Ground water level data
CD-Rainfall method
It uses the assumption that in normal conditions
groundwater levels quickly react to rainfall:

Above average rainfall results in an increase
of water tables.

Below average rainfall results in a decline
Recharge - Rainfall
1. Water level – Mean rainfall
2. Water level – Above mean rainfall
3. Water level – Below mean rainfall
In the CD rainfall you calculate:
 Departure (difference) from normal rainfall for the
period
 Then calculate the cumulative departure (=CD)
 And compare this with groundwater levels
Take a close look at the next table >>
CALCULATION OF CUMULATIVE DEPARTURE RAINFALL (CD-RAINFALL)
MONTHS
RAINFALL
DEPARTURE
CD RAINFALL
WATER LEVEL
J
50
-76,5
923,5
2
F
90
-36,5
887
1,9
M
175
48,5
935,5
2,2
A
230
103,5
1039
2,4
M
310
183,5
1222,5
2,8
J
300
173,5
1396
3,3
J
229
98,5
1494,5
3,5
A
105
-21,5
1473
3,4
S
30
-96,5
1376,5
3,2
O
5
-121,5
1255
2,8
N
0
-126,5
1128,5
2,6
D
0
-126,5
1002
2,2
TOTAL RAINFALL
AVERAGE MONTHLY RAINFALL
1524
127
Difference
with monthly
average
Cumulative
departure
Comparing the ‘cumulative rainfall
departure’ with groundwater levels
allows us to understand recharge and
overuse
‘No overuse’:
Water level follows CD-rainfall
Rainfall – water level relation
400
400
Average rainfall
300
200
200
100
100
cd
rainfall
‘No over-use’:
0
Water level J
follows CD2000
rainfall
1500
1000
500
0
0
F
M
A
M
J
J
A
S
O
N
D
4
CD RAINFALL
WATER LEVEL
J
F M A M J
J
A S O N D
CD rainfall - Cumulative departure from average rainfall
2
0
water
level
Rainfall
300
Average Rainfall
Rainfall
Another ‘normal’ situation
Overuse:
water level drops even though
CD rainfall goes up
Recharge and discharge to a river:
The relation between CD-rainfall and
water levels is not clear
Presentation based on
work of Wim Boehmer