GROUNDWATER GEOLOGY OF ALLUVIAL FAN AQUIFERS LOCATED IN THE WESTERN THIRD OF THE GWYDIR RIVER VALLEY, NEW SOUTH WALES, AUSTRALIA

Abstract

ABSTRACTOne hundred eighteen water wells located in the western third of the Gwydir River Valley are studied for their log data. Well depths, aquifer thickness, maximum water yields and geographic location data are tabulated, mapped, and correlated in order to determine the location and extent of good water‐yielding aquifers within the alluvial fan in which they are located. These aquifers consist of sand, gravel, and basaltic alluvium located at varying depths in distributary channels extending westward through the fan. There are four identified aquifers, the deepest one is situated from 75 feet to 250 feet below the fan's sloping surface. This aquifer has a maximum capacity for water‐yield totalling 180,000 gallons per hour from 30 wells. The three other aquifers are situated at less depth within the fan, each sloping downward to the west from near Moree. These 45 wells have a total maximum water yield of about 138,000 gallons per hour. The 43 remaining wells studied have low water‐yields totalling 7000 gph. The surface expression of these high‐yield aquifer channels may become a guide to locating favorable sites in drilling for additional supplies of ground water suitable for extended irrigation requirements.SUMMARYWell‐log data from 118 wells located in the lower part of the Gwydir river watershed are studied. These data reveal the nature and extent of aquifers in the alluvial fan situated below Moree. Information on the recharge of these aquifers is found in a study of the climate, physiography, and geology of the upper two‐thirds of teh Gwydir river watershed. It is noted that recharge water comes from the runoff water from the mountainous upper one‐third of the watershed; and from water filled fractured rocks of the faulted zone in the middle of the watershed. In addition to this recharge of the alluvial fan aquifers some five miles above Moree from subsurface runoff located higher in the watershed, considerable recharge from surface floodwater takes place in the lower third of the watershed from the surface of the alluvial fan into the subsurface aquifers by downward bleeding.