The baseflow-duration curve, A technique for the study of groundwater discharge from a drainage basin

The baseflow-duration curve provides a technique for the comparative study of base runoff from the same or different drainage basins. The curve is a cumulative frequency curve showing the percentage of time that specified base flows were equaled or exceeded during a given time period. Daily base flows are obtained from a hydrograph separation of base and surface runoff. Although the separation may not be precise, the value of the technique as a comparative tool is not lost as long as a consistent method of separation is followed. When bank storage is present within a basin, the base runoff can be separated on the hydrograph into two components, designated bank- and basin-storage discharge. These are differentiated on the baseflow–duration curve by the shape of the curve. Thus, the baseflow-duration curve allows comparisons not only of total base runoff but also of the base runoff components. Examples illustrating the use of the technique show that (1) the texture of the surficial deposits largely controls the discharge from basin storage, (2) the width of the permeable deposits adjacent to the river greatly influences the amount of bank storage discharged, (3) the mean annual amount and variation of bank storage may be several times that of basin storage, and (4) one typical water year provides enough hydrologic data for a valid comparative study of base runoff from segments of the same drainage basin.