Water indicators
Water quality: The criteria for good water quality for irrigation are: low salinity or low ratio of Na+ to Ca2+ Mg2+ to prevent the development of sodicity; and small concentrations of those ions which may have specific toxic effects. The index used most often to characterize the quality of irrigation water with respect to its influence on the exchangeable sodium percentage is the sodium adsorption ratio (SAR) which is defined as follows:
SAR = [Na+] / {([Ca2+] + [Mg2+])/2** (1/2).
This is the ratio of the sodium ion (Na+) concentration to the square root of the average concentration of the divalent calcium (Ca2+) and magnesium (Mg2+) ions. The concentrations are expressed in moles per litter. Electrical conductivity can be used as an easy measurement for the purpose of this project. The following classes are used <400 , 400-800, 800-1500, >1500 μS.
Water quantity: Knowledge of water resources of a region are of great importance for the local economy. The hydrological regime of a region or a watershed is a crucial prerequisite for any hydrological work. Groundwater resources include deep and shallow aquifers that are connected to rivers, streams or seas. For a quantitative analysis it is important to have sound estimates of the recharge of the aquifer over a given time period as well as its interactions with surface waters (recharge and discharge). For an assessment of groundwater resources it is essential to have repeated observations of groundwater levels at a relatively large number of observation wells, since groundwater systems respond to short-term and long-term changes in climate, groundwater withdrawal and (artificial) recharge and land uses. Surface waters encompass both rivers and lakes and can quantitatively be assessed by long term averages of the available water resulting from endogenous precipitation. Temporal variations also have to be taken into account.
Ground water exploitation: can be estimated by "the exploitation index" that is defined as withdrawal of conventional freshwater resources (surface and groundwater) over total renewable resources (expressed in %). Ground water over-exploitation describes the degree to which the amount of water pumped from aquifers is sustainable in relation to the water that is available. This indicator considers the potential supply in relation to what is actually used. Over-exploitation can be quantitatively analysed by comparing groundwater recharge amounts with the amount of water actually used, but it can also be seen from undesirable effects such as the drop in well levels, disappearance of rivers and springs, and salinization. This indicator is estimated by assessing: (a) water consumption by various sectors, (b) the decrease in river and spring flow, ground water monitoring and (c) comparing by an appraisal of the recharge rate in a certain hydrological area.
Water consumption/water demands: The amount of water used and the corresponding demands by domestic, industry, agriculture and other sectors (that includes private and public services) are computed. The percentage of total consumption by each sector dividing the total consumption or by the corresponding demands for each sector determines the indicator. In this project, the total consumption in all sectors versus the total demands is used. The following classes are used for this indicator: low (water consumption/water demands (WC/WD <0.5), moderate (WC/WD = 0.5-1), high (WC/WD = 1-2), and very high (WC/WD >2).
