filter efficiencyfilter packfilter stripfiltering mediumfiltratefiltrationfiltration springfinal stagefine noncohesive soilfine rackfine sandfine screenfine texturefinesfing grainedfinite difference time stepingfinite differencesfinite elementsfinite increments methodfiordfirebreakfirmfirnfirst fillingfirst order climatological stationfirst significant precipitationfirthfissurefissure springfissure waterfive day forecastfive point methodfixationfixed bed modelfixed ground waterfixed modelfixed time increment modelfixed time stepfixed wheel gatefjordflape gateflared outletflash floodflash streamflatflat crested measuring weirflexibility croppingfloatfloat barographfloat device