rational methodrational mwthodravinereachreactivereal specific gravityrecessionrecession curverecession velocityrechargerecharge arearecharge basinrecharge wellreclaimreclamationreclamation drought indexreconnaissancereconnaissance surveyrecorderrecording rain gagerecording rain gaugerecoveryrecovery of velocity headrectanglerectangular broad crested weirsrectangular cross sectionrectangular drainage patternrectilinear flowrecurrence intervalrecursive procedurered rainreduced gravityreduced tillagereduciblereductionreferencereflected wavereflectionreflection coefficientreforestationrefractionregelationregenerated waterregimeregimenregolithregosolsregressionregularity agencyregulated flow