Dumanli Spring, Turkey — The largest karstic spring in the world?

Abstract

The enormous Dumanli spring in the Mediterranean region of Turkey will be submerged by the year 1982 by about 120 m head produced by the Oymapinar Reservoir. The spring contributes one third to the annual discharge of the Manavgat River, that will be dammed at Oymapinar. The mean discharge of the spring is estimated at about 50 rmm 3/s; thus its total annual outflow is about 1.6 · 10 9 m 3. In October 1978 the authors measured the spring discharge by the dye-dilution technique. The flow rate of about 35.6 m 3/s at the very end of the dry period (at the end of the spring's discharge recession) motivated the authors to declare the Dumanli the largest karstic spring in the world, issuing from one single orifice. The results of the dye-dilution technique applied in this experiment were compared with staff-gauge readings upstream and downstream of the Dumanli spring. To the best of the authors' knowledge this is the first reported dye-dilution experiment that accurately measured the discharge of a river with an annual flow of about 50 m 3/s. To permit a better appreciation of the size of the aquifer drained by the Dumanli, a recession hydrograph of differences in the flow downstream and upstream of the Dumanli is presented. This hydrograph is a cumulative one of several springs between two gauging stations but the Dumanli itself contributes at least 90%. When interpreted in the sense of a standard recession-curve analysis the following can be concluded: (1) the Dumanli plus several smaller karstic springs discharge in the dry five months of the year about 630 · 10 6 m 3; (2) near the end of the recession period about 1370 · 10 6 m 3 still remain in storage; (3) the coefficient of recession is of the order of magnitude 0.0026 day −1 thus pointing to a very large drainage system, high storage volume, and slow drainage; and (4) the drainage area contributing to the Dumanli appears to be of the order of magnitude of about 1200–1500 km 2.