Wednesday, March 30, 2011


Groundwater is prime natural resources in the earth .Not only it supported almost all types of life form to evolve, but also helped in growth of human civilization. It quenches thirst and meets the household demands. Used in the fields for production of food grains .Lastly the industries catering to the various needs and luxuries of human being have started consuming voluminous quantity of Water .Groundwater is therefore a precious national asset and planning, development and Management of water resources need to be governed by national perspectives.
In the beginning, water from rainfall and snow and rivers were only source of water to mankind. As these surface water sources were dependent on rainfall, localized shortage was often witnessed. With primitive technologies men was not able to build sustainable water reservoir to see them through the drought period .But once man came to know of groundwater, his dependence on it increased with the advent of civilization. At present about two billion people in the world is dependent on groundwater. Fortunately, groundwater is a renewable resource that is recharged every year through rainfall. However, this recharging process is not entirely dependent on rainfall but on various other natural factors that differ from region to region and within space and time. Therefore, recharge of groundwater is never a constant factor .When the average quantity of draft exceeds recharge for repeated years we face the situation of over exploitation.
The manner and the scale in which the use of groundwater has accelerated, human being has become so much dependent on the assured source that no sign of the over increasing demand for groundwater stabilizing.
Beginning of 20th century witnessed demand for groundwater in industrial sector rising phenomenally at a faster rate than that in agriculture and domestic sector.
West Bengal is the only state in India that stretches from Mountain to the Sea and truly a “Asamudra himachalam” state as the meaning goes. West Bengal has a very good groundwater potential. The reason of such affluence is due to her geographical location, high rainfall and favorable geological setting .The state have land area of about 2.7% but have about 6% of total replenishible groundwater resources of India. Groundwater is the most exploited resource in west Bengal particularly in agriculture sector With the introduction of water intensive high yielding variety , the need for groundwater have skyrocketed. Quinquennial census of minor irrigation structures indicated a 64% growth in number of STWs over last 16 years,@4% annually.
Table Showing Number of Groundwater Structures from 1986 to 2001

Name of Structure 1986-87 1994-95 2000-2001
Dug Well 63387 55983 39377
Shallow Tubewell 368316 504638 603667
Deep Tubewell 3122 4039 5139

Hydrogeological Condition
Geologically West Bengal can be divided into two broad units (A) Consolidated or semi consolidated formation occurring in the northern most and western part of West Bengal and (B) Unconsolidated formation in the rest of West Bengal.
(A) Consolidated/ semi consolidated formations:
These formations cover the western and the northern part of the state. These are comprised of Archaean crystalline rocks and Gondwana group of rocks including Rajmahal traps covering part of Purulia, Bankura Paschim Medinipur, Birbhum and Burdwan.. Archaean metamorphics, Siwalik and Gondwana covers part of Darjeeling and Jalpaiguri District. In the western part and in some part of Darjeeling district , these hard and semi consolidated rocks are overlain by weathered residuum and laterite capping.
(B) Unconsolidated formations:
These formations belonging to the Tertiary and Quaternary age and covering rest of West Bengal. These formations may be subdivided into (a) Secondary laterite (b) Older alluvium and (c) Recent alluvium.

Secondary laterite occurs at the marginal area between the Consolidated/ semi-consolidated rock and older alluvium mainly in the districts of Bankura, Paschim Medinipur, Burdwan and Birbhum. Older alluvium occurs mainly in the elevated terraces fringing the lateritic margin of the Chhotonagpur plateau in Bankura, Pascim Medinipur, Burdwan, Birbhum, Hoogli and Murshidabad district and in the Barind region of North Bengal. Recent sediments occupy the river courses and flood plains.

Depletion of groundwater
In spite of having high groundwater reserve, exploitation of the resources in West Bengal shot up to such level that 80’s decade first witnessed the sign of depletion of groundwater level in some blocks of Murshidabad, Burdwan, Medinipur, Hoogly where pre-monsoon water level dropped below the centrifugal pumping limit and hand tubewells went dry. Introduction of Submersible motor driven pump though came as a blessing to the cultivators, for it can draw water from far deeper depth – caused further lowering of groundwater level.
Depth to water level data analyzed by the State Water Investigation Directorate, Govt. of W. Bengal, indicated significant average annual fall in pre monsoon depth to water level during the period 1995 to 2004 to the tune of 16 to 70 centimeters in some blocks of Murshidabad, Burdwan, Purba Medinipur and Hoogly districts. In some parts of Hooghly, Burdwan and Murshidabad districts, significant fall was noticed in both pre and post monsoon period.

Case 1 No change

Case 2- Post monsoon no change but pre monsoon falling trend

Case 3 both pre & post monsoon show falling trend

Case 4: Pre monsoon rising trend, post monsoon falling.

Groundwater Quality
In addition to the phenomenon of lowering of water level, deterioration in Chemical quality of groundwater was noticed in some parts of the state that took place in the form of Arsenic and Fluoride contamination. On the basis of preliminary survey 81 blocks in the state have been identified where Arsenic was found in groundwater above permissible limit. Similarly, presence of Fluoride beyond permissible limit in groundwater was detected in 49 blocks of the State.
It was observed that the entire younger and recent alluvium formation east of Bhagirathi River is arsenic bearing and reason for such occurrence is solely Geogenic. Arsenic held by the solid phases within the sediments, especially iron oxides, organic matter and sulphides might constitute the primary arsenic sources in groundwater under condition condusive to arsenic release from solid phases.
Occurrence of Fluoride, in groundwater is generally recorded from hard rock areas. The subsurface water may be contaminated with dissolved substance due to disintegration and dissolution of bed rock that rendered water unfit for drinking due to presence of certain toxic constituents. Fluoride is one such chronic toxic substance, that have affected large number of people causing Skeletal or Dental fluorosis. Fluorite (CaF2), Cryolite (Na Al F6) is the rock forming minerals which contribute Fluoride to the groundwater. Wastewater containing Fluoride originating from various industries viz phosphate fertilizer, ceramic industry brick kiln and pharmaceutical industries may find its way to the groundwater and elevate the Fluoride level.

Assessment of Groundwater Resources
Apprehending phenomenal increase in extraction of Groundwater, Government of India considered that quantitative assessment of these resources is necessary for planning and sustainable development. Accordingly , Ministry of water Resources formed Groundwater Estimation Committee , which came out with a methodology based on reasonably valid scientific principles and reliable data .The first assessment of the resources was carried out in 1984. Meanwhile, Central Groundwater Board and different State Water investigation Organizations carried out further detailed studies and generated additional database which along with the ever-rising Groundwater utilization through the country, indicated need for modifying the methodology for more precise assessment. Another Estimation Committee was set up in 1995 came out with modified methodology in 1997 known as GEC ’97 methodology. Assessment of Groundwater resources of all the States were carried out jointly by the Central Groundwater Board and the respective State groundwater Organizations with block as unit and 2004 as base year.
The assessment revealed that the national average for stage of groundwater development is 58% whereas the same for the State of West Bengal is 42%.The assessed blocks were categorized, on the basis of stage of development and long term significant decline of groundwater level, as ‘Safe’, ‘Semi-Critical’, ‘Critical’ and ‘Over exploited’ .In the national scenario, 4078 blocks are Safe out of total 5723 blocks.
In West Bengal assessment was carried out in 269 blocks out of total 341 blocks leaving aside 13 hilly blocks in the north and 59 Saline blocks of coastal region. As per the assessment carried out by application of GEC’97 methodology, 231 blocks have been found to be Safe .28 blocks were assessed to be Semi-Critical and 10 blocks as Critical. However State committee on groundwater assessment is reviewing assessment and categorization of this 10block.
Based on the assessment carried out the net groundwater availability in West Bengal was calculated to be 27.46 BCM, whereas existing groundwater draft in all sectors –irrigation , domestic and industrial , is 11.65 BCM, leaving 15.81 BCM of dynamic resources reserve for further use.
Planned approach for Groundwater development
The groundwater scenario at national level and that of West Bengal reveal that exploitation of groundwater in the state has not yet reached alarming critical stage .The national water policy 2002 states that exploitation of groundwater should be limited to the extent of annual recharge. Although the average stage of groundwater development is 42% in the state , adverse effects like water level depletion and chemical degradation have been noticed in some areas in scattered manner. Government is concerned about incidents of suffering of the local population in such areas due to shortage of water in peak summer and from diseases due to consumption of arsenic and fluoride contaminated water.
It was apprehended that if indiscriminate use of water go on unabated, adverse effects of degrading hydrogeological regime of the state, will amplify and will engulf the whole state in such a manner that the whole agriculture and industrial development process will suffer a set back. The Government had determined view not to allow such situation and decided to promulgate suitable Act to control and regulate the use of groundwater in the State.

Groundwater Act
West Bengal Groundwater Resources (Management , Control & Regulation ) Act 2005 was promulgated with effect from 15th September ‘2005.This act stipulates obtaining mandatory permit for installation of groundwater extraction structures operated by engine or motor driven pump .This act also , stipulate registration of all such structures existed before the act came into force.
Apart from West Bengal, other states viz. Himachal Pradesh, Kerala, Goa and Tamil Nadu have already passed suitable acts for control and regulation of groundwater .Andra Pradesh had enacted Water , land and tree act in 2002. Maharashtra enacted groundwater (regulation for drinking water sources) Act in 1993 for limited purpose of regulating public drinking water. For the remaining states either the groundwater bill is under drafting or draft bill is under consideration of the respective government.

Crisis of Water is probably the worst curse any civilization would like to face. It will be tragic for the next generation facing this crisis due to lack of foresight in part of the present generation. The groundwater resources, although renewable, are limited and vulnerable. Crisis of water may not be only quantitative; quality degradation may also add a different dimension to the problem.

West Bengal, which is considered to have tremendous groundwater potentialities, is no exception. Crunch is already felt in drinking water sector in rural west Bengal during Boro cultivation season precipitating a situation of artificial draught in almost every year. Unpredictable monsoons, destruction of green coverage, siltation of rivers, uncontrolled urbanization have compounded this problem. Area under arsenic and fluoride are increasing day by day. Failures in part of the authority to implement the Groundwater Act and lack of awareness in part of the users have failed to check unrestricted growth of tubewells in the state. Stages of groundwater development with 2004 as base year that show a meager 42% stages of groundwater development in the state as against a national average of 58% , needs to be upgraded .The 4th Minor Irrigation Census is presently underway and results might reflect a higher Stages of groundwater development for this state. The act for controlling extraction of groundwater is probably not adequate in itself for total management of groundwater resources unless people is made to aware about the adverse situation which may arise from unplanned and indiscriminate use of groundwater. The other strategies involve co-ordinate approach to conservation, augmentation and conjunctive use of groundwater, wherever possible. This can be successfully achieved through rain water harvesting and artificial recharge that make it possible to:
1. Restore supply in aquifer, depleted due to overexploitation.
2. Improve chemical quality
3. Prevent salinity ingress.
4. Increase hydrostatic pressure against land subsidence

To implement rain water harvesting and artificial recharge to be implemented , it is necessary to adopt policy decisions like mandatory installation of roof top rain water harvesting and artificial recharge structures in urban areas and restoration of all derelict tanks in the villages , building check dams etc in high slope areas.
Groundwater is not an isolated resource. It is a phenomenon within the hydrological cycle. So depending on the hydrogeological condition, water level condition and stage of development proper measure for augmentation of groundwater should be taken.

When the Fukushima Meltdown Hits Groundwater

When the Fukushima Meltdown Hits Groundwater

The Fukushima disaster may take a new turn if it strikes groundwater. The concrete material being poured on it to cover the radioactive emission is of no use, because the nuclear reaction in the plant could not be stopped. The temperature in the reactor would melt the concrete and it would act like lava. The molten material may reach the groundwater table. If it happens there will be more violent explosion and this may be a nightmare beyond Chernobyl.

Saturday, March 12, 2011

Does Gas Drilling Put Radiation in Texas Water?

Does Gas Drilling Put Radiation in Texas Water?

  • With new shale discoveries in south-central Texas, the state's natural gas production is poised to grow, as The Texas Tribune reports today.

    A variety of environmental concerns have arisen over shale drilling, however. The best-known of these involve chemical pollution of aquifers and the air. A recent New York Times series, focused on Pennsylvania's Marcellus Shale, raised additional questions about whether or not radioactive materials are ending up in that state's waterways as a result of wastewater from drilling operations. (State findings released subsequent to the article show that the radiation levels are at or below normal in some streams near drilling operations, but investigations are continuing.)

    The Tribune asked the Texas Railroad Commission, which oversees the natural gas drilling industry, and the Texas Commission on Environmental Quality, the state's main environmental regulator, whether Texans need to worry about radioactivity in their water. 

    Here are their e-mailed responses (edited slightly for clarity):

    From Ramona Nye, Texas Railroad Commission spokeswoman:

    In Texas, unlike Pennsylvania, where [hydraulic fracturing] fluid is treated and then discharged to surface waters, the majority of the frac flowback water and produced water in Texas from the oilfield is disposed of in injection disposal wells and back into underground, geologically confined intervals. The commission has issued one authorization to the Barnett Shale Water Conservation Company to dispose of oilfield wastewater in the city of Fort Worth’s water treatment plant. The commission authorizes this proposed disposal provided the TCEQ (which permits discharges from water treatment plants) and the facility owner or operator concur.

    Additionally, the commission’s wellbore construction regulations also protect groundwater by requiring several layers of steel casing protection when these injection or disposal wells are built.

    While indications are that flow-back fluid from hydraulically fracturing the Marcellus Shale in the northeast, including Pennsylvania, can contain elevated levels of radium-226, Oil and Gas Division Commission staff inform me that they have no indication that radium-226 levels are above regulatory levels in the Barnett Shale or the Eagle Ford Shale in Texas, which are geologically different shales than Pennsylvania Marcellus shale.

    Gas wells can bring Naturally Occurring Radioactive Material (NORM) to the surface in the cuttings, flow back fluid and production brine, and NORM can accumulate in pipes and tanks (as scale on pipe after long periods of time).

    Oil and gas NORM waste must be managed in accordance with the provisions of the Railroad Commission’s rules at 16 TAC Chapter 4. Operators are required to monitor for the presence of oil and gas NORM, and if the levels exceed the permissible level of activity at a particular site, the site must have requisite placards alerting persons to its existence. NORM waste may only be disposed of at sites that are specifically permitted for oil and gas NORM waste disposal.

    From Terry Clawson, TCEQ spokesman:

    The TCEQ Water Supply Division ensures that all community public water systems are tested for radiation in accordance with the federal Radionuclides Rule. The TCEQ does not have jurisdiction to regulate private water wells; therefore, we do not monitor them for Raionuclides. The TCEQ Water Supply Division sampling has not detected elevated levels of radionuclides in public water systems located near gas-drilling sites. The Railroad Commission of Texas has the authority and responsibility to oversee drilling and related disposal activities in the state of Texas.

    This article originally appeared in The Texas Tribune at

    Saturday, March 5, 2011



    A systematic hydrogeological study was carried out in the project area covering about…6500…ha. The survey includes geological and geomorphological mapping, periodic monitoring of water levels in a network of observation wells. 100% dugwells in the area have been selected as monitoring stations. Lithological log upto a depth of 10m (bgl) were obtained in certain areas to determine the geometry of the aquifers. Geomorphological and structural mapping was carried out in a larger area to determine the regional geology and trends of lineaments.

    Complete geological mapping has been done on this area. The geology of the area is it is a granitic region with minor variation in the grain size. There is a pegmatite outcrop in the Sarenga Fulberia. There are basic intrusions in granite, which has a foliation dip and strike.

    Geomorphologically the area can be subdivided as:

    1. Denudation terraces

    2. Shallow buried pediments

    3. Moderately buried pediments

    4. Valley fill deposits

    The above four categories of geomorphological surfaces have been separately dealt with in the hydrogeological investigations as follows.

    1. Pumping tests : Pumping tests to determine the aquifer parameters were carried out in a number of dugwells in the area. The wells were essentially situated in the Baid and Kanali area. The recuperation test data were analysed in G.W.W. programme and Kd (Transmissivity) value was determined.

    2. Infiltration experiment: Infiltration experiments were carried out in the project area for determination of infiltration capacity. The infiltration capacity values are determined to classify the watershed in terms of infiltration capacity.

    3. Monitoring of water level: From 160 nos. observation wells of water table below ground surface has been monitored every month. From these data pre-monsoon and post- monsoon depth to water level maps and water level fluctuation maps have been prepared.

    4. Reduced level connection of wells: All wells have been connected by land level survey and reduced level (RL) of each well was determined. Thus RL of water table at each well point in each season was computed. Seasonal water table contour maps have been prepa- red to determine the groundwater flow direction and the geometry of the saturated surface.

    5. Stream discharge measurements : At the mouth of the Chaggalkuta stream gauging station has been set up to measure the stream discharge continuously.

    6. Meteorological Observations: Primary meteorological data have been generated at the weather station set up at Teghori village. Daily precipitation, sunshine, wind speed, rate of evaporation, maximum and minimum temperature, humidity etc. are continuously recorded at this station. With the help of necessary meteorological data daily PET (Pennman) has been computed with the help of a programme prepared for this purpose.

    7. Soil Moisture: Monthly soil moisture percentage has been gauged at every land situation at 15 cm and 30 cm depth. With this data monthly change in soil moisture has been determined.

    Aquifer Condition: The basement rock of Chagalkutta watershed is mainly granite along with some pegmatite and basic intrusive. Fractures in this rock system generated the secondary porosity. The weathered residuum and the thin alluvium cover that lie over the basement rock contain water and these along with the fractured part of the basement rock developed the treatic aquifer system. This area has a single unconfined aquifer and thickness is between 15 to 30m as revealed from local information of dug wells and hand tube wells. But these tube wells and dug wells are mostly confined to the ridge, back slope and rarely to the toe slope and valley region. There is hardly any well in the valley fills.

    212 (100%) dug wells are monitored every month. It is very difficult to take water level from the drinking water tube wells because the local people do not allow opening of those hand pumps. So the present observations are totally based on the data available from those 212 wells.

    It is observed that the wells are in most cases occur as clusters in settlement areas in some cases spacing between two wells is very small to generate contour lines between them. So 50 wells have randomly been selected for water level map generation water table contour maps have also been generated by RL connection data of those wells.

    All contour maps and depth to water level zonation maps have been prepared with the help of SURFER-6 software and for better interpolation and extrapolation kriging method has been adopted for grid generation. Each depth to water level grid file and each contour grid file have been blanked with watershed.bln.

    Depth to water level condition: Pre-monsoon and post-monsoon depth to water level maps have been prepared using the table (well.xls). The map shows that in the chhagalkuta watershed there is wide variation in the pre-monsoon water level (April 1999). The maximum depth to water level condition has been observed at Lakhanpur (well no. Lak 1) where the water level is 14.30 mbgl. At Golghori wide variation in water level is observed (5.05m to 11.05m) bgl. At Siromanipur, Danga, Kurchibedia, Kasibedia, etc. area water level is between 8 to 9m bgl. But it is observed that in most of the wells other than those described above major area of the watershed has depth to water level between 6 to 7m bgl. At Gopaldihi, Panjangora, one well at Kendsar (ken 1) shows water level below 5m and 2 wells at Gopaldih (Gop 1 and Gop 5) show water level within 4m bgl. The depth to water level map divided the watershed in depth to water level zones.

    1) Between 3-6m bgl i.e. within centrifugal pumping limit

    2) From 6-7m bgl i.e. sump well is possible

    3) From 7-10m bgl i.e. beyond centrifugal pumping limit but within low HP submersible

    Pumping limit.

    4) Above 10m bgl i.e. special pumping device or high HP submersible pump is required.

    Post monsoon depth to water level map (November) shows a remarkable rise in water level. It is to be mentioned that at Lakhanpur the rise is maximum (11 to 12m approximately). During the post monsoon period major part of the watershed show depth to water level between 2 to 3m bgl. Only at Kasibedia, Poirasol, Kanudih and Ghutia. Post-monsoon water level is between 3 and 5.5m. In the western ridge area i.e. at Dangra Lari and Kendsar and Panjangora in the south, the fluctuation is minimum (75m). There are some isolated patches showing fluctuation between 7 and 9m (at Danga).

    Groundwater flow direction

    Water table contour maps generated during pre and post monsoon period show the major trend in groundwater flow. Pre-monsoon water table rises upto 160m amsl at the southwestern corner of the watershed and comes to 99m amsl at the month of the Chhagalkota stream. The overall groundwater flow direction is from southwest to northeast in conformity with the surface.

    During the post-monsoon period overall flow direction does not change much excepting with a rise in level. In the southwestern corner the R.L. of water table is about 165m amsl. In the northernmost corner of the watershed i.e. near the mouth of Chhagalkuta this value is about 103m amsl.


    1. Purpose and scope:

    Hydrological analysis carried out in Chagalkuta watershed started from February 1999. All investigations were conducted from the field station situated at Teghari in Chhatna block of Bankura district. The field station is equipped with all types of meteorological and hydrological gauging provisions

    2. Parameters:

    For detailed hydrological analysis the following parameters had been analysed in details.

    i) Precipitation

    ii) Potential evapotranspiration

    iii) Soil moisture

    iv) Pond water volume

    v) Groundwater dynamic storage

    vi) Runoff

    vii) Groundwater draft

    viii) Actual evapotranspiration

    3. Basic data Generation:

    For calculation of each of the above-mentioned parameters primary data have been generated from field and then computed. The table below shows the list of field database and frequency of reading behind each of the parameters mentioned above.

    Table showing List of field database behind each hydrological parameter

    Sl No.


    Field Data base

    Reading frequency



    Potential evapotranspiration

    Sunshine hour


    Wind speed

    Mean air temperature

    Relative humidity



    Rain gauge reading



    Soil moisture

    Soil moisture %



    Pond water volume

    Field measurement from pond



    Evaporation from pond

    Pond surface area



    Groundwater dynamic storage

    Depth to water level




    Measurement from stream



    Groundwater draft

    Human use / irrigation draft/



    Actual evapotranspiration

    Crop area for each crop


    4. Method of data collection.

    The methods of collection of different types of field data are described below.

    I. Daily sunshine hour is recorded from sunshine recorder installed at Teghai field station.

    II. Daily maximum and minimum temperature is recorded using maximum-minimum thermometer and Stevenson’s screen. Mean daily air temperature is calculated from the readings.

    III. Daily relative humidity is collected using hygrometer.

    IV. Anemometer is used to collect the wind velocity. Daily two readings are collected and daily average wind speed is calculated.

    V. Daily reading from rain gauge is collected at the hydro-meteorological station at Teghari..

    VI. Daily evaporation rate is measured using pan evaporimeter.

    VII. There are dug wells within the watershed area. Depth of water level from ground level is measured from each well every month.

    VIII. The wet area and depth of each pond is measured every month to calculate the monthly pond volume.

    IX. There is a gauging station at the confluence of Chagalkutta with Arkosa. At that point the daily stream flow is measured using flow meter.

    X. The population of each mouza is an indicator of groundwater draft. In this area people depend mostly on ground water for their domestic use. Multiplying the population with the daily water use and the number of days in a month the groundwater draft is calculated.

    XI. Soil moisture data are collected from the field using soil moisture meter, which gives the percentage of available water.

    XII. Area of each crop is recorded in every month.

    5. Computation

    a) Computation of Potential evapotranspiration: this is calculated using Penman’s equation:-

    PET= (AHn + Eag)/(A+g)

    Where PET = daily potential evapotranspiration in mm per day

    A= slope of the saturated vapour pressure vs. temperature curve at the mean air temperature, in mm of mercury per oC. This value is achieved from the Table M1

    Hn = net radiation in mm of evaporable water per day

    Ea = parameter including wind velocity and saturtion deficit

    g = psychrometric constant = 0.49 mm of mercury / oC

    The net radiation is expressed as Hn= Ha (1-r) [a+bn/N] -st4a ( 0.56-0.092ea )[0.10+0.90n/N]

    Where Ha= incident solar radiation outside the atmosphere on a horizontal surface, expressed in mm of evaporable water per day ( it is a function of latitude and the period of the year as computed in table M2)

    a = a constant depending upon the latitude Φ and is given by a= 0.29 cos Φ

    b = a constant with an average value of 0.52

    n = actual duration of bright sunlight in hour

    N = maximum possible hour of bright sunshine (it is a function of latitude as indicated in table M3)

    r = soil albedo

    s = Stefan- Boltzman constant= 2.01 X 10-9 mm/day

    Ta = mean air temperature in degrees Kelvin = 273 + oC

    ea = actual mean vapour pressure in the air in mm of mercury

    The parameter Ea is estimated as Ea = 0.35 [1+ u2/160] (ew-ea] in which

    u2 = mean wind speed at 2m above ground in km/day

    ew = saturation vapour pressure at mean air temperature in mm of mercury this is defined as a function of temperature and the equation is = 4.584 exp [17.27t/ ( 273.3+t)]

    ea = actual vapour pressure

    For computation of PET the following basic data are necessary:- Latitude, Elevation, Mean temperature, Mean relative humidity, Observed sunshine hour, Wind velocity at 2m height, Nature of surface cover, Date of observation.

    b) Computation of Soil Moisture volume: Soil moisture was monitored periodically. Soil moisture percentage data have been gauged from every mouza and every land situation in every month. For computation of monthly water balance, monthly average soil moisture percentage for every land situation was calculated first. From monthly soil moisture percentage soil depth of each land situation and soil character, soil moisture depth and volume have been computed. The following conditions hereby apply. For determining field capacity and wilting point a graph (fig 3.8) of page 65 from the book Hydrology and Management of Watershed by Keneth. N. Brookes, Peter F. Ffolliott , Haus. M Gregersen and Leonardo F Dabauo have been consulted. The table shows the average root depth, field capacity, wilting point and soil water holding capacity.

    Soil water holding capacity (mm)=Root zone soil depth (m) x {Field capacity (mm) –Wilting point (mm)}

    Land situation

    Average Root Zone Soil Depth (m)

    Field capacity (mm)

    Wilting point (mm)

    Soil moisture holding capacity (mm)






    Back Slope





    Toe Slope





    Valley Fill





    From soil moisture % soil moisture depth of each land situation for each month has been calculated.

    Soil moisture volume (in ham) was calculated as = Soil moisture percentage x Soil moisture holding capacity (in mm) x area (in ha) x .001

    c) Computation of Groundwater recharge/ discharge: Ground water level (depth to water level) has been measured in every well in every month. Water level fluctuation of each well for each month with respect to previous month was calculated.

    From mouzawise average fluctuation groundwater recharge and discharge have been calculated using the equation; Recharge / Discharge = Fluctuation x Area x Specific Yield

    Since the total area falls within a granitic country and the aquifer mainly comprises of weathered and fractured granite the specific yield has been assumed as 0.05.

    d) Computation of Pond volume:

    Actual pond water volume of every month was measured (average depth x area) for every pond. Monthly total pond water storage was calculated from that value.

    e) Computation of Actual Evapotranspiration:

    Actual evapotranspiration (AET) has been calculated from the potential evapotranspiration (PET) using the following equation :

    ET (vol ) in ham = PET (mm) x S Crop & other vegetation Area (ha ) x Crop Coefficient (kc) for each crop x (0. 001)

    f) Computation of evaporation from surface water bodies: Evaporation from surface water bodies is calculated using the following equation.

    Evaporation in a month = pond surface area (Ha)* evaporation from pan evaporimeter (mm)* pan factor

    In this case the pan factor is 0.70


    The fundamental water balance equation used in this project is a modification of the Thornthwith Mather model in which groundwater recharge/ discharge and groundwater draft have been included. Thus the principal water balance equation is

    P + surplus water of previous month + I = AET+ D Sm. + DGW + D Pond + evaporation + GW Draft + Runoff + Surplus water retained in the system at the end of the month.

    Here P= precipitation volume

    I = Irrigation input

    AET = actual evapotranspiration

    D Sm = change in soil moisture volume

    DGW = Change in groundwater storage (recharge/ discharge)

    D Pond = Change in pond storage

    Table Showing the parameters and their mathematical relations involved in calculating the water balance

    Item No





    Water retained in the system at the end of previous month (+ve value=surplus, -ve value = deficit)



    Precipitation measured for the month * area of the watershed



    Actual irrigation input in the field, calculated on the basis of irrigated crop pattern and area



    Total of Water retained in the system at the end of previous month+ precipitation volume+ Irrigation input



    Soil moisture volume of previous month - soil moisture volume of current month



    Pond volume in the previous month – pond volume in the current month



    Average change in groundwater level * area of watershed* specific yield

    [+ve value means recharge into, -ve value means discharge from the reserve]



    Total of Abstraction of water in reserves= soil moisture change+ pond volume change+ groundwater recharge/ discharge



    Actual evapotranspiration based on Crop area* crop coefficient*PET



    Evaporation from wetlands






    Total of AET+EVAP+RUNOFF




    Total water input-Total abstraction of water in reserves-Total water loss[+ve value means water surplus and -ve value means water deficit ]

    6. Water Estimation:

    Water estimation is done to achieve at a conclusion that for a particular time and space there must be a tool for assessing the available water at any part of the whole system.

    Thus the whole system is divided into three parts, i) water gaining system, ii) Water storage system and the iii) discharging system (water loss)

    Water gain of the system is Precipitation, Irrigation (in case of the Chagalkutta watershed it is nil as no irrigation is being received from outside), and cumulative change of soil moisture storage, change in pond water volume, change in ground water volume. Total water loss from the system occurs as Evaporation loss, Actual ET, ground water seepage loss, and run off. The difference in water gain and water loss is the quantum of water that remains impounded within the system through various water harvesting structures excluding the traditional pond/tank system. It was found that some surplus water is generated within the system. It is explained that a huge amount of water is kept stored in the field (impounded) by the local people from the very first month of the monsoon to minimize runoff. But, how much water is stored cannot be quantified. Soil moisture is also measured from comparatively dry areas; therefore the surplus water is actually the artificial and temporary impoundment, which subsequently drains into streams or groundwater. So, for rational calculation the surplus water found in a month is added to the total water input of the next month.