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Published byImogen Welch Modified over 9 years ago
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CD-Rainfall method A quick method to make a groundwater balance
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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
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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:
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Recharge - Rainfall 1.Water level – Mean rainfall 2.Water level – Above mean rainfall 3.Water level – Below mean rainfall
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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 >>
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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
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Comparing the ‘cumulative rainfall departure’ with groundwater levels allows us to understand recharge and overuse
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‘No overuse’: Water level follows CD-rainfall Rainfall – water level relation ‘No over-use’: Water level follows CD- rainfall
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Another ‘normal’ situation
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Overuse: water level drops even though CD rainfall goes up
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Recharge and discharge to a river: The relation between CD-rainfall and water levels is not clear
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Presentation based on work of Wim Boehmer
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