02094naa a2200241 a 450000100080000000500110000800800410001910000180006024500890007826000060016752015380017365000130171165000090172465000100173365000100174365000130175365000220176665000140178865000090180265300170181165300130182877300110184110733641993-06-03               bl ---       0--  u    #d1 aCHILDS, E. C.  aThe water equipotentials and streamlines in drained landbV. the moving water table.  c0  aThe method of electric analogues as applied to drainage problems is extended to deal with the case of a rising or falling water table, that is, to the unsteady state following  changes of rate of rainfall, with a system of equidistantly spaced drains. It is shown that, over a very considerable range of movement following cessation of rain, starting rom a steady state and continuing until the water  table is but little  is but  little higher than the drain level, the water table falls as a whole without appreciable change of shape, after which it naturally falls more slowly over the drain line than elsewhere, since the distance left to fall is samller. The  relation between water-table height and time is shown for various horizontal distances from the drain.The water table approaches drain level asymptotically but not, except fortuitously, exponentially, since the  heigt-time curve has a different shape for cach distance from the drain line. Over the range where the water table falls without change of shape, it also rises without change of shape when rainfall is resumed. Consequently, the average water table during the period of fluctuation coincides with the water table for steady rainfall of some average instensity, always provided that the movement is not carried outside this range. When the initial state is that of saturation to the soil surface istead of a steady state corresponding to constant rainfall, cessation of rainfall is followed at first by a faster fall of water table over the drainline than...  adrainage  asoil  awater  aÁgua  aDrenagem  aLençol Freático  aMovimento  aSolo  aGround water  aMovement  ts.n.t.