The HBV model of these systems may be assessed using the Nash–Sutcliffe efficiency coefficient. A geometric progression of these systems is postulated by Horton’s laws, which strengthen Playfair’s (15[1])description of these systems’ incision. (15[1])A namesake “continuum concept” models these systems as dynamically stable ecosystems. Sharp changes in gradients of these systems called (*) knickpoints can be caused by rejuvenation. Strahler numbers were developed (10[1]-5[1])to describe the bifurcation of these systems, which engage in downcutting to form terraces. These systems are flanked by a riparian zone where they may deposit eroded material as alluvium. For 10 points, name these hydrological systems whose branching defines basins that drain to a delta. ■END■ (10[1])