No abstract

A 0.3028‐ha watershed has been instrumented to monitor streamflow and subsurface flow through the soil mantle at a variety of topographic locations. The watershed is forested, with steep (35°) slopes and shallow (average 55 cm) soils on impermeable Old Man gravels. Data for a number of storms indicate that subsurface flow via ‘macropores’ (root channels, pipes) and seepage zones in the soil is the predominant mechanism of channel stormflow generation in storms with quickflows greater than about 1 mm. Subsurface flow from all parts of the watershed appears to contribute to stormflow even in very small storms (quickflow of the order of 3% of net precipitation). The saturated hydraulic conductivity of the soil matrix is not a limiting factor on the ability of subsurface flow to generate channel stormflow, because dye tracer experiments demonstrate that water may move through macropores (particularly root channels) at rates 2 orders of magnitude greater. However, subsurface flow from lower slope areas contributes to delayed flow; cessation of subsurface flow and Streamflow after a drought period is roughly coincident in time. In the study area it appears that streamflow is at almost all times dominated by subsurface flow and that runoff from partial and variable source areas contributes significant quantities of streamflow only during the rising limb of small (less than 1 mm of quickflow) flood hydrographs.

No abstract

Constant discharges of 26.5, 56.7, 105,240, and 507 m3s -1 were released down the Ohau River from Ohau A power station, and measurements of water depths and mean velocities made along cross sections in a braided section of the channel. Frequency distributions of water depth and velocity are presented both singly and jointly for each discharge; the methods used provide much more information on the changing character of the fiver than is provided by conventional hydraulic geometry relations. As discharge increases, existing channels become wider, deeper, and faster and frequently merge to become a single larger channel. However, additional channels are generated with the same characteristics as those existing at lower discharges, and the total number of channels at a cross-section remains constant. Hence the increase of water surface area tends to be by addition of faster, deeper water to a constant area of shallow, slow water (whose location in the river bed changes). This process has the major implication for instream uses such as salmonid spawning in that the area suitable for these uses may remain constant over a wide range of flows. In some respects, then, the braided river is morphologically more stable than a single-thread river. -26.5 ß ß ell ß ß ß ß ß ß ß ß ß ß ß ß . ß ß ß ß © ß ß ß _ ß ' '14 9-16..... '25 ß <1 4-9 16-25 thousand m 2 --105 ß , e ß © ß . ß ß ß ß 0 ß ß ß ß ß ß ß ß ß ß ß ß ß ß ß _ _ .... 56.7 ß ß eOe. ß _ ß ß ß el O ß ß ß ß ß _ ß ß ß O ß ß . ß ß ß ß _ . ß _ _ ß ß -240 ß eeO©. ß --_ ß Oe oil. ß ß --_ ß ß ß ß ß 0 ß ß ß ß --_ ß oOoO ß ß ß ß ß _ _ --_ ß --_ ß --_

No abstract