water treatment filtration through a granular bed
This figure also illustrates the impact made by the water depth over the medium a first type of filter curves 1 2 3 with m of water over the sand will allow in order to maintain a minimum positive pressure see p min curve 3 2 m of head of fouling whereas a second type of filter curves 4 5 6 with m of water will only allow m of head of fouling and therefore a far