Welsh Journals

Soil pipe networks: distribution and discharge J. A. A. JONES Lecturer in Geography, University College of Wales, Aberystwythì V In an admirable call for more information on the location and response characteristics of soil pipe systems in upland Wales, Newson (1976) has outlined the results of current research by the Institute of Hydrology in their Plynlimon catchments. Many of the points raised by Newson merit some comment in the light of the author's own experience, particularly in the Maesnant basin on the opposite side of Plynlimon and in Derbyshire. First of all, the potential significance of soil pipe discharge to theories of catchment response must be emphasised. Not only do pipes provide a form of combining flow system within what is commonly regarded as a purely diffuse flow medium (Liao and Scheidegger, 1968), but they also provide throughput velocities for storm drainage which are comparable with both the classic "Hortonian excess" overland flow (Horton, 1945) and the more recent concept of saturation overland flow (e.g. Dunne and Black, 1970a and b; Hewlett and Nutter 1970; Hewlett, 1974). Measured stormflow velocities of Maesnant were up to c.o. 15 ms', compared with c. 0.2 m š' to c. 0.8 m š' in the Brecon Beacons (Wilson, 1977) and c. 0.1 m š' in the Mendips (Weyman, 1975, 12). Piping may both augment saturation overland flow (Knapp, 1970, 170) and offer a comparable alternative route across the "alluvial toeslope" (Dalrymple, Blong and Conacher, 1968). Yet at present we still lack an overall picture of the field situation, despite recent attempts to monitor pipe discharge and quantify its importance to stream response by Stagg (1974), Lewin, Cryer and Harrison (1974), Jones (1975), Wilson (1977) and Newson (1976), of which the last five attempts have all been in the Welsh uplands. Not surprisingly, there is still no account taken of piping in general models of basin response (cf. Hewlett and Nutter, 1970; Weyman, 1975) or even in recent computer models (e.g. Chidley and Goodwill, 1975). Distribution in Britain The initial problem for current field studies is to determine the location and distribution of piping. Clearly, it is not ubiquitous even in the uplands, but the handful of British locations previously cited