The paper argues that watershed management has to be fluid to take into consideration new realities like change in flow conditions, external realities like unintended impacts and the need to maintain minimum downstream flows for environmental and other purposes.
The principles that have guided policies for watershed management have not changed over the years though there has been an increase in intensive agriculture, increase in rainwater harvesting and improving rain-fed agriculture. This research paper is an effort to determine whether there is a need for changes in policy in response to the catchment closures at the basin level and lowering of volumes of water flowing into village reservoirs.
Citing other studies, the paper argues that watershed development projects may not been actually providing the positive benefits of providing water and improving livelihoods. Other watershed interventions like land use changes through increasing area under irrigation, forestry, agro-forestry etc, can alter catchment flows (evaporative or liquid water flows) resulting in unforeseen and negative results.
The paper analyses a study done by Department for International Development (DFID) on the Inchegeri catchment and a World Bank study done on the Mustoor catchment. The interventions in these catchment areas include rainwater harvesting structures, tank rehabilitation, use of bore-well to increase area under irrigation, intensification of agricultural activities etc. The two catchment areas differ in soil types, geology, concentration of rainwater harvesting structures, irrigation bore-wells. However both areas have seen an intensification of farming systems including better seeds, more fertiliser etc.
The paper analyses the Hydrological Land Use Change (HYLUC) Models made for these two areas. For Inchigeri surface runoff calculations were based on land use distribution in the sub catchment areas. The model showed that even without interventions introduced by Karnataka Watershed Development Society (KAWAD) annual outflows from the Inchigeri tank was a small (3.1%) of the rainfall. After intervention the value was reduced to 1.8%.
In the case of the Mustoor catchment area the impacts of siltation of tanks was also studied. The HYLUC model underestimated the tank spill frequencies in the early period of record and overestimated the frequencies in the most recent period. After investigating the causes it was concluded that it was not because of rainfall but because of abstraction of groundwater and water retention because of agricultural intensification which included land based engineering interventions including bund construction and improved rain-fed farming systems.
The societal impact of these studies analysed by the current paper determined that families were using less domestic water than the national norm even during rains. Open wells that were the source for domestic water were defunct. Bore-wells are dug to greater depths today, but the rate of failure is high.
In their conclusion the authors make the point that rainwater harvesting structures need not be more efficient in retaining water than large tanks or reservoirs. They also add that watershed development planning in India must nowo be based on analysis of biophysical charecteristics of the area and the spatial and temporal patterns of water demand in the area while also looking into externalities and trade-offs. Planners can no longer use existing thumb-rules for water shed management.
The paper can be downloaded from the journal website here.