in contrast the imposition of collective management schemes has led to mixed results the use of local management districts in parts of the high plains region of the united states has allowed spatial variations in implemented groundwater use rules to be established that are decided by farmer members of district boards of directors and tailored to local needs eg nebraska dnr and urnrd nebraska dnr and mrnrd in spain the water act imposed the creation of water user group to manage the overexploitation of aquifers but in many cases the result has not been successful iziquierdo et al