India's arid areas appear to have some experience with 'check dams' for precisely this purpose - turning monsoonal wet seasons into year-round wellwater.
Digging ditches is much less cost-effective for this purpose than building small dams, though they seem to have also worked with those, ditches filled with rocks under a cover and used as a storage tank.
http://lawschool.unm.edu/nrj/volumes/48/3/03_agoramoorthy_in...
http://www.researchgate.net/publication/247773763_A_review_o...
http://www.iwmi.cgiar.org/Publications/CABI_Publications/CA_...
Digging ditches is much less cost-effective for this purpose than building small dams, though they seem to have also worked with those, ditches filled with rocks under a cover and used as a storage tank.