Tanzania Journal of Agricultural Sciences 1999, Vol. 2(2): 239 - 242Macro-catchment raiilwater harvesting (RWH) describes those techniques witll much larger Catchment Areas (CAs) (generally > > Iha) which generally do not fall witllin a farmer's land. The CAs and Cropped basins (CBs) will often be very different in character and tlle transfer d.istance may be in tile range of a few hundred metres to several kilometres'- Although runotf efficiency is relatively lower tllan thy. 'microcatchment systems, runoff volumes will still be large because of tlle size of tlle CA. If the transfer distance is very large, it is also possible for tlle CA to receive rain and produce runoff for a CB which has received no rain. Macro-catchment RWH systems include: hillside systems such as tlle "ma jaluba" system of tlle Lake Zone of Tanzania (Meertens et aZ" 1999) where, water is ~hannelled intp bunded rice padis by small channekconstructed across ,tlle slope on grazing land; stream-bed systems which spread water tlowing in ephemeral streams using permeable stone dams or earth b~nds (van Dijk and Ahmed, 1993); and stt-eam diversion systems which chamlel water , trbm ephemeral streams into water-spreading s&uctures such a~ tlle "Caag" system of Somalik (Reij, 1991) The mairi problems with these : s~stems are, in controlling tlle sometimes very high volumes of runoff and preventing erosion. I The risk of too' much water washing away tiblds is a major problem in Western Pare I - Lowlands (WPLL).