1. CD-Rainfall method A quick method to make a groundwater balance

2. 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

3. CD-Rainfall method  Above average rainfall results in an increase of water tables.  Below average rainfall results in a decline It uses the assumption that in normal conditions groundwater levels quickly react to rainfall:

4. Recharge - Rainfall 1.Water level – Mean rainfall 2.Water level – Above mean rainfall 3.Water level – Below mean rainfall

5. 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 >>

6. CALCULATION OF CUMULATIVE DEPARTURE RAINFALL (CD-RAINFALL) MONTHSRAINFALLDEPARTURECD RAINFALLWATER LEVEL J50-76,5923,52 F90-36,58871,9 M17548,5935,52,2 A230103,510392,4 M310183,51222,52,8 J300173,513963,3 J22998,51494,53,5 A105-21,514733,4 S30-96,51376,53,2 O5-121,512552,8 N0-126,51128,52,6 D0-126,510022,2 TOTAL RAINFALL1524 AVERAGE MONTHLY RAINFALL127 Difference with monthly average Cumulative departure

7. Comparing the ‘cumulative rainfall departure’ with groundwater levels allows us to understand recharge and overuse

8. ‘No overuse’: Water level follows CD-rainfall Rainfall – water level relation ‘No over-use’: Water level follows CD- rainfall

9. Another ‘normal’ situation

10. Overuse: water level drops even though CD rainfall goes up

11. Recharge and discharge to a river: The relation between CD-rainfall and water levels is not clear

12. Presentation based on work of Wim Boehmer