What is renewable water resource?
The renewable water resource is that water which gets replenished every annual cycle through monsoon rains. If water use exceeds renewable water availability that invariably implies overexploitation of the water resource, i.e. of groundwater and any other water body that carries water from earlier years.
Surface water is a resource that cannot be exploited beyond availability. Similarly, soil moisture, another measurable resource, cannot be exploited beyond availability.
Exhaustion of groundwater in source (dug well or bore well) is a sure sign of exploitation of nonrenewable groundwater.
Deeper drilling following the decline of water levels is p leading to another peril, apart from increased pumping energy requirement, of geogenic causes of water contamination. Arsenic and fluoride contamination is widely known. But there are pockets of other heavy metals and even of radioactive substances.
An aquifer regaining its water level is a sure sign of water renewability. Sustainable management of water resources requires use of only the renewable water resource.
Integrated Water and Land management model for low rainfall
The multiple objectives of sustainable management of rural livelihoods and water resources, building resilience to climate change, and reversing the carbon footprint requirement a fresh approach to land and water resources use.
While it will make sense that in low rainfall areas irrigated agriculture should be on limited lands so that sufficient water is made available to irrigated crops butwater from precipitation, as replenished soil moisture, will still be getting utilised as evapotranspiration. Therefore when we consider ecosystem productivity it is still necessary to utilise this water as efficiently as possible and make the resultant produce work for livelihood security in the ecosystem.
Presently rainfed crops are largely in the framework of food-fodder crops where edible produce contributes to food security and the biomass is utilised as fodder. The remaining rainfed lands are mainly used as pastures or grazing lands with some of them exclusively reserved for lopping as hay. These lands are eventually burnt due to a blind belief that this improves the grass productivity during the next monsoon. Any natural shrubs are used as fuel and lopped before the lands are set afire.
The present land and water use pattern may be classified as follows:
• Croplands with protective irrigation during monsoon, usually dual purpose of food security and marketable surplus
• Some parts of the above may be utilised for post monsoon irrigated commercial crops
• Remaining parts may post monsoon receive limited irrigation for food security-cum-commercial crops
• Purely rainfed crops during monsoon, again dual purpose.
• Part of the rain fed lands may be utilised for post monsoon water efficient crops purely on the basis of residual soil moisture.
• Purely rainfed grasses with a sprinkling of shrubs.
• Some amount of so called social forestry.
In a 500 mm rainfall regime it may be possible to have following cropping pattern:
• Food security crops including appropriate proportions of grains, pulses and oil seeds on about 20% arable lands with protective irrigation during monsoon, and critical irrigation during post monsoon for water efficient extended kharif crops and/or short duration winter crops. Of this 2/5th or 8% of total may be for food security for local community and 3/5th or 12% of total for marketable surplus.
• About 0.005% of lands for vegetable crops to provide nutrients and mother and child care
• 10% of lands for irrigated fodder which can be preserved as green fodder for use during summer
• The remaining, i.e nearly 70%, would be for various types of “managed” dry land plantations, which may include fodder and fuel, horticulture, biomass required for preventive pest management, vegetation that support water conservation, and energy and industrial biomass. Most biomass will have a direct commercial value.
Communities and technical support groups need to first of all conduct water balance investigations and water availability arithmetic. If 40% of rainfall is used in situ through good soil moisture conservation techniques and 40% is permanently lost without use there will be about 20% available for applied irrigation. This will amount to over 3,000 m 3 per ha for irrigated food security and fodder crops.
More, if the plantation productivity in dry biomass terms is about 20 kg per ha-mm, for 200 mm in situ use the total production per ha would be 4 tonnes per ha. If daily biomass consumption of a milch animal is 20 kg in dry terms, i.e. about 7.5 t per year, biomass from 2 ha can support one animal.
Similarly, biomass from irrigated fodder will support 2.5 animals per ha. Therefore a 100 ha plantation will support nearly 250 animals with good milk productivity..
It may be possible to enhance water and land use productivity by raising nursery plants and transplanting them so as to reduce on-field time. This has further advantage that 3-4 week plants transplanted with advent of monsoon will make more productive use of available soil moisture; similarly the second crop will make better use of season ending rains; and it may become possible to squeeze in two short duration crops or one extended Kharif crop.
Groundwater recharge guidelines
Groundwater recharge has always been an important part of the wish-list in water conservation programs. However, a systematic effort to develop a robust science of recharge has been lacking, in the absence of which it has only received a lip-service.
It is necessary to combine good science with good common-sense for effective recharge. The good science part is scientific demarcation of run-off, recharge and discharge zones. The run-off zones are areas where there is very poor potential for recharge through natural geomorphological formations. Recharge zones are areas where there is good potential for recharge through natural formations. Whereas, discharge zones are areas where aquifers actually release waters.
With this robust understanding of geomorphology with respect to groundwater recharge the good common sense is -
a. Construction of water conservation structures on recharge zones to effect recharge taking advantage of natural recharge facilitating conditions.
b. Construction of recharge shafts in storage areas of conservation structures where geomorphological formations don't support recharge.
It should stand to reason that conservation structures may cause evaporation loss of conserved water. Therefore it is necessary to evaluate different conservation structures with respect to potential to cause evaporation losses if above two conditions are not being met.
i. Check-dams: These will certainly cause evaporation losses. However, circumstances of dire necessity, such as very poor groundwater storage capacity, such structures will be necessary, though only as part of scientifically planned water management strategy.
ii. Continuous Contour and other Trenches: These will also most certainly cause evaporation losses and should not at all be constructed outside recharge zones. Such structures are not conducive to artificial recharge either. Continuous Contour and other Bunds should be preferred on areas outside recharge zones that are not conducive to natural recharge.
Enhancing renewable groundwater availability
It should stand to reason that aquifer should have some empty cavities if it is to accommodate recharged water. Recharge from rains takes place during monsoon. The general model would be -
• Run-off causing precipitation
• Filling up of conservation structures
• Recharge
This cycle will repeat itself if there is empty space in aquifer when the next run-off causing precipitation event takes place. Therefore either there has been a downstream flow from the aquifer, discharge in discharge zone and/or pumping from the aquifer whereby it can accommodate more recharge. The first two are slow processes. It should stand to reason that the win-win situation is where water is pumped out for protective irrigation repeatedly when aquifers are full. The last rains should fill up the aquifers and conservation structures so that some water is available for post monsoon use.
Minimizing groundwater pumping Energy requirement
A centrifugal pump gives best energy efficiency for a particular discharge rate and pumping head. The main variable in the latter is the water level in the water source. The key parameter in designing an energy efficient pumping system is the replenishment rate of the water source, i.e. the rate at which water flows in to the water source. If the discharge rate from the pumping system is matched with the replenishment rate the water level will remain steady and the system will give good efficiency.
If the discharge rate is higher than replenishment rate the water level will go down and their may come a point when the source is totally dried up. At this point the pumping system will have to be switched off and the user will have to wait till some replenishment takes place before it is switched on again.
When the pumping system is switched on the first time in the day the piped conveyance system will get filled up before it starts discharging water in the storage tank. When the system has to be switched off due to exhaustion of the source the water in the pipes is most likely to leak out, to an extent that depends upon the waiting duration, due to even minor leakages or air vents. Thereafter, when the system is switched on again the piped conveyance system will have to get filled again before it starts discharging. This cycle gets repeated the number of times the system is switched off and on during a pumping schedule. All the water that gets leaked out is at the least partially preventable loss if all the water requirement is pumped in one single session - which in turn is possible if the discharge rate is matched with replenishment rate.
Initiating water management projects
How a project is initiated determines the final outcome, i.e. equity, sustainability and cost to benefit ratio. Equity is an outcome of a protocol among beneficiaries to allocate available water equitably among all potential beneficiaries. Sustainability is an outcome of another protocol among beneficiaries where total withdrawal is equal to renewable water resource and effective repair and maintenance of conservation structures and other assets through direct labour as well as financial contributions. The best way of mobilising O&M costs is in the form of water charges for delivered water. Cost to benefit ratios depend upon the total value generated over the life span of assets as against total costs including initial investments, O&M over the lifespan and depreciation costs.
This calls for a comprehensive agreement among beneficiaries on protocols for sharing water, paying for the water service and making the most efficient use of available water. Such agreements are best evolved prior to making investments on conservation as it is nearly impossible to evolve them once water availability is enhanced and the new use pattern gets established. Even if a protocol is evolved prior to investments there is no guarantee of its survival if the protocol does not get translated in to enhancement of incomes to the extent that they meet expectations of the beneficiaries.
The key is to develop capabilities of farmers to efficiently cultivate and collectively market water efficient cropping patterns where net incomes are comparable to water intensive crops. This capability building should take place simultaneously with micro planning for conservation so that both, the water availability as well benefits from water efficient cropping pattern are clear to the beneficiaries at the time of formulating protocols and there is greater commitment towards them. The investments on conservation should only be taken up for small, homogenous groups of farmers who achieve discernible results from capability building inputs and accept protocols on equitable, sustainable and productive use of water. This will also send a clear message to the target area that performance will be rewarded and those who lack will be bypassed. This strategy has better chance to succeed.
The purpose of the investments should not be stated as “augmenting water resource” or “enhancing water availability” or “conserving water”, it should be stated as enhancing farmer incomes through enhancement of water and land use productivity and collective marketing”, and this should be the true objective: win-win situation where farmers benefit.
Measuring water resources and developing water balance model
If something is to be managed it is necessary to know how much of it there is and how it is being used and how it should be used, i.e. to measure it. Water balance model is all about estimating water availability, present uses and evaluating various options for water and land use.
Water balance requires knowing net water in the storages, inflows, outflows, consumption or use and losses.
Storages are in the form of surface storages, aquifer storages and soil moisture.
Consumption or use is by/for humans, livestock, industry, municipal bodies and vegetation.
Losses are mainly evaporation from surface storages & soils, transpiration by vegetation, and open channel conveyance.
Inflows are as precipitation, surface flows and groundwater flows.
Outflows are in the form of surface flows and groundwater flows.
Typically the data that may be commonly, historically available is rain gauge data, satellite sensors data, reservoir data, and river stage data, all from prefixed sources at specific points or in grids.
Typically the affordable and robust instruments that are available for measurements are - manual and automatic rain gauges, pan evaporimeters, water current meter, dug and bore well water level sensors, soil moisture sensors, and various weather sensors of which most important for water balance computations are precipitation, humidity, temperature, wind speed and solar radiation. The weather sensors can be available in a compact package called automatic micro weather station.
Additional but very important data necessary for evaluating evapotranspiration by vegetation is - a) land use classification and pattern with particular attention to vegetation and cropping pattern. A general classification as forests, wastelands, agriculture is grossly insufficient; an accurate estimation of lands under different crops and vegetation will enable a correspondingly more dependable water balance, and b) crop productivities. The former is best obtained from high resolution multichromatic imagery and the latter through participatory investigations.
Similarly estimation of rainfall and pan evaporation requires a high accuracy GIS platform and GIS tools for geographical analysis.
Also similarly, estimation of soil moisture, local water resource augmentation as also evaporation from surface flows requires GIS tools and ground information like soil types and other geomorphic patterns.
Making conservation work for poorly endowed farms & habitats
Poor endowment on a permanent basis is due to two natural settings - poor rainfall at the area or region level and upper catchments with respect to topography and surface hydrology. Drought as such is a temporary phenomenon due to temporary national (poor monsoon all over India) and regional scale (poor monsoon in some regions) conditions. Drought should not be confused with poor rainfall areas that receive relatively low rainfall as permanent climatic feature. In the central and peninsular India this occurs due to rain shadow effect of western ghats. The upper catchments of rain shadow regions are particularly poorly endowed. The lower valley regions are relatively better endowed due to natural surface and sub surface flows from upper areas to lower areas. In the lower areas the primary issue is sustainable and equitable management of available resources. Further, any effort for conserving water in the upper areas benefits the lower areas as a natural consequence. Therefore the primary issue is how to make conservation work for the poorly endowed areas!
It is assumed that all the issues discussed in all other advisories here above and elsewhere in the website are most relevant to such areas. The main remaining issue is bringing scientific and engineering excellence in surface water harvesting.
There are two key scientific applications required. The first is high vertical accuracy Digital Elevation Model and related products such as small basins demarcation, slope demarcation, drainage lines, etc.
The target areas will more often constitute the basins of lower orders of drainages, e.g. 1st to 4th order, which are normally not captured in the low vertical accuracy DEMs.
Slope demarcation is important for area level treatment (Continuous Contour Trenches, Contour Bundhs, etc.). Drainage line identification along with basin demarcation is important for optimised design of check dams to maximise trapping of available rainfall, locating water impounding, silt trapping and flow velocity reduction structures, and evaluating engineering parameters like maximum length of drainage, average slope, catchment area, etc. required for technically sound designs of structures.
The second key scientific application is estimating rainfall. This can be done using ground observatory data and/or satellite sensors based data. Interpolation using GIS platform is required for rainfall estimates. Rainfall estimates, number of run-off generating storm events, frequently occurring high rainfall intensity, etc. parameters are important for optimised drainage line treatment.
Inviting New Partners
We Invite more collaborative Partners to expand collective capabilities and bringing
in newer and newer aspects on the resource management agenda. Of particular
interest are fields like taxonomy, agronomy, energy and industrial biomass and
biomass based technologies. Also of much interest are livestock and livestock based
technologies and products.