Basin Tracer Curves Interpreted by Basic Calcutta

A basin flow tracer test with pulse injection is essentially passage of a material shock wave. Virtual transit is related to the maximum slope on the dimensionless time versus concentration curve. The plug point, separating plug from non-plug flow, is located at the initial arrival of tracer for straight rising or convex upward ascents, and hypothetically at the first tangential subinflectum of ogive ascents. Plug fraction of flow extends from the origin to the plug point; dual flow exists from the plug point to the descending inflectum, beyond that flow is the mixed or eddied type. Short circuiting is indicated directly by the distance between plug point and nominal detention time. The negative exponent of the semi-logarithmic plot of the decline denotes the number of times the effective fraction of basin volume is extracted by non-plug flow. Curves replotted from the literature confirm this theory. Dispersion is measured by the angle between the tangent to the plug point with the vertical. A concise diagram having plug point and dispersion as coordinates permits comparison of basins.