Water resources development and management
In river basin studies, the
applications of averages for hydrological parameters are meaningless
since supply and demand are not evenly distributed over time and
space in river basin. Following are to be done for a rigorous
assessment. An intervention model for average ten day stream flow
forecast and synthesis. The digital simulation of a drainage basin
to convert rainfall into abstractions and surface runoff. The exact
and approximate evaluations of the storage distribution in a water
reservoir are not rigorous. The likely performance of water
resources systems is often described by the mean of various
benefits, pollutant concentrations or some operating variable. Take
for instance the case for a groundwater system. Quantum of water
which can be extracted economically from under ground every year is
generally reckoned in engineering circles as groundwater potential.
This implies that water extracted in any year should be returned to
the aquifers in the form of recharge from the succeeding
precipitation or recharge, so that over a cycle of two, three or
five years the groundwater table does not go down progressively. In
these cases also simple averaging do not help in resources
assessment.
With RS technology being
the major source of spatial data on natural resources and when
combined with other data sets - conventional maps, GPS data, census
data and so on, will offer an information packet, hitherto
unavailable to the decision maker. With the availability of
information packet, GIS technology and applications will impact most
of our resource management and decision making in a major way.
Remote sensing based water quality assesment
Remote Sensing with its unique capabilities of synoptic coverage, repetitively and capturing features of inaccessible areas like reservoir water contours and crop water use zones (CWZ) has been effectively used in monitoring reservoir water use (water budgeting) and irrigated crop water use to assess the performance of main system management aspects of large scale irrigation systems.
Reservoir water use budgeting in a typical multipurpose reservoir
The following procedure was used to arrive at actual/realisable amount of water that is available for use in the reservoir-command during the time interval of satellite overpasses. Reservoir water spread area (water contours) obtained from satellite data every fortnight during rabi/summer season are used in assessing water quantity available between satellite overpasses. Water budgeting is carried out.
Reservoir working tables can thus be updated once in 22 days/15 days - till such time as all the components of water balance into a "stochastic reservoir" are arrived at using time series/intervention models and "phase" of lake budget is calculated. The above procedure results in actual amount of water that is available for use in the command during the time interval of satellite overpasses.
The results of the above procedure helps in assessing the following in a river basin/part of a river basin. The possible effect of negative inflows in a river as arrived at in daily water budgeting tables used in operation of a reservoir. The above has a bearing on upstream water utilisation (being less than actually recorded utilisation).
The working tables used for water balancing at sub-basin level gets a check on their parameter values if satellite data is used at appropriate times. The check on carry-over storage at basin level will become precious for correct valuation of water utilisation at both upstream and down stream users.
Remote sensing derived crop water use zones
The characteristic spectral signature of
vegetation in the visible and near infrared bands was recognised early in the history of remote sensing. It is perhaps surprising that satellite remote sensing techniques have found few "real world" application in agriculture (irrigated or dryland both). Satellite systems that have the resolution to recognise individual fields are constrained to repeat cycles that are too long to characterise the growing season of a typical annual/seasonal crop. The problem becomes much more complicated in small land holdings, having mixed cropping and multiple cropping systems with varied agricultural management practices.
A water quantity variable namely crop water use zone (CWZ) has been delineated using remotely sensed IRS images. It includes consumptive use by crops and land. Three CWZ describing heavy, medium and light water use zones in a CCA can be mapped with it. These CWZ have been used to define four irrigation performance indicators which represent the uniformity, adequacy, equity and dependability of irrigation water distribution at main system level in a large scale irrigation system.
Using the above, the following can be assessed which helps in river basin/sub-basin water use assessment in a rational manner. The water utilisation (not water requirements of crops) in each command (a part of sub-basin) can be had from satellite imageries when one establish relations.
The satellite derived water utilisation helps in assessing irrigation performance of each command area projects with water as the main input. These maps of water utilisation helps in planning for better conjunctive use. Farmers participation in irrigation management increases because the current method(s) of measuring discharges only at distribution head and gauging water height at sub-distribution or pipe-outlet level - and a whole of lot of statistics for the season wise distribution of water are not comprehensible by farmers. A map depicting water use is going toincrease their awareness and hence better participation. It helps in comparing financial and irrigation performance of divisional/sub-divisional jurisdictions.