A well-established inverse relationship exists between mean scallop length and flow vel~city fo~ a given population of scallops. Previous authors have suggested that one or more 'sc~llop dominant diScharges' can be identified at which erosion by dissolution proceeds at the ?Teatest rate, Since scallop. populations usually indicate a single flow velocity whereas discharge and velOCity are unsteady throu~ tIme. For vadose conduits, a scallop dominant discharge is difficult to de~ne because of the unconstrained crosssection; this causes problems in determining the discharge at whIch scallops are forme?, althou~ recent developments in instrumentation allow greater flexibility in monitoring flow~ on a continUOUS b~ls. Here the relationships between monitored flow velocity and depth are compare? ~Ith the scallop velOCIty fo: an active vadose streamway in Poulnagollum, Co. Clare, Ireland. From these InItIal results, a complex relatIOnship is seen to exist between the velocity and depth of flow as discharge changes. Thr~sholds o~c~ over discrete depth ranges where there is little or no change in velocity; these are observed dunng both nsmg and falling stage. It is suggested that these thresholds may be related to changes in hydraulic radius, and hence flow resistance at different depths of flow. The scallop-derived velocity is related ~o the record~ flow data, with reference to the various controls on erosion, most notably the degree to whIch the flow IS undersaturated with CaC03, and ongoing research is outlined.