Tributary-trunk stream relations in a cut-and-fill landscape: a case studyfrom Wolumla catchment, New South Wales, Australia

At the time of European settlement of the south coast of New South Wales, A ustralia, in the mid-nineteenth century, river courses were discontinuous t hroughout Wolumla catchment. Within a few decades of settlement, intact val ley fills had been transformed into incised channels along trunk streams. T his induced associated patterns of secondary incision into tributary valley fills. Three of the primary subcatchments in Wolumla catchment became full y incised, while an upland swamp and a floodout (i.e., sand sheet deposits atop an intact valley floor) remain in mid-catchment of the fourth subcatch ment. Of the 70 lower order tributaries which join the trunk streams in the four subcatchments, 27 have incised (12 of which are discontinuously incis ed). Incision of tributary streams in Wolumla catchment cannot be explained by subcatchment area and slope relations. The position of the trunk stream channel within the valley floor trough is the key determinant of whether o r not tributary streams have incised. Changes to river morphology since Eur opean settlement have altered the linkage of tributary streams to the trunk stream, impacting directly on the within-catchment transfer of water and s ediment. (C) 1999 Elsevier Science B.V. All rights reserved.