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USING

GEC-97 methodolog

y

WATER BALANCE

STUDY

Hydrogeological Map of India

Background First time in 1979, the ground water resources were estimated using a methodology

recommended by, 'Committee on Over-exploitation of Ground Water Resources‘ constituted by Agriculture Refinance and Development Corporation (ARDC).

In 1984, the methodology was modified by a committee known as 'Ground Water Resources Estimation Committee (GEC)'. Upon completion of the assessment of ground water resources of the country, GEC-1984 was used.

Again in 1997, the Ground Water Estimation Committee reviewed the previous studies and work done in various states and suggested a modified methodology in 1997 (GEC’97) for computation of ground water resources.

To get a more appropriate methodology for ground water resources estimation for hard rock terrain, which will supplement the GEC-1997, Ministry of Water Resources, Govt. of India, constituted a committee (and revised GEC-97) on 03.09.2001.

Source : Dynamics GW Resource 2011( CGWB, 2014) , Report on the Hard Rock Ground Water Estimation (CGWB)

Precipitation

reaching surface

Infiltration

Infiltration Rivers

Joints, depressions,

rivulets

Surface Runoff And

interflow

Infiltration

E

E

EE

Direct Recharge Indirect RechargeLocalized Recharge

E E

E = Evapotranspiration

Schematic representation of Recharge

Salient features of their recommendations are given below

Hard rock areas the assessment is made with respect to watershed unit.

The total geographical area is divided into subareas such as hilly regions (slope > 20%), saline groundwater areas, canal command areas and non-command areas, and assessment is made separately for all these subareas

During the non-monsoon period recharge from rainfall and other sources is based on the Rainfall Infiltration Factor and other prescribed norms

Norms for return flow from groundwater and surface water irrigation are revised taking into account the source of water (groundwater/surface water), type of crop (paddy/non-paddy) and depth of groundwater level

There should be at least 3 spatially well-distributed observation wells in the unit, or one observation well per 100 sq. km. whichever is more

Categorization of assessment unit is to be governed by long term water trends besides the stage of development

Source: GROUNDWATER ASSESSMENT METHODOLOGY - C. P. Kumar Scientist ‘F’, National Institute of Hydrology, Roorkee, Report on the Hard Rock Ground Water Estimation, By CGWB

WATER BALANCE EQUATION The following equation is a generalized form of water balance equation, which applies to any

assessment unit irrespective of it being an administrative unit, a watershed or an aquifer. This water balance equation holds good for any part of the year and for the annual water balance as well.

ΔS=𝑅𝑟𝑎𝑖𝑛𝑓𝑎𝑙𝑙 + 𝑅other − − 𝐵 𝐺𝐸𝑎𝑙𝑙 − ± ± 𝐸𝑇 𝐿 𝑂 /𝑖𝑛𝑓𝑙𝑜𝑤 𝑜𝑢𝑡𝑓𝑙𝑜𝑤

ΔS =Change in storage in ground water reservoir𝑅𝑟𝑎𝑖𝑛𝑓𝑎𝑙𝑙 =Recharge from rainfall𝑅other =Recharge from other sourcesB = Base flow𝐺𝐸all = Ground water draft for all uses𝐸𝑇 = Evapotranspiration losses𝐿 =Leakage to or from deeper aquifers

O /𝑖𝑛𝑓𝑙𝑜𝑤 𝑜𝑢𝑡𝑓𝑙𝑜𝑤 =Net inflow/outflow across the boundary of the assessment unit or

ΔS=𝑅𝑟𝑎𝑖𝑛𝑓𝑎𝑙𝑙 + 𝑅other − 𝐺𝐸 𝑎𝑙𝑙 ± 𝑉𝑜𝑢𝑡𝑛𝑒𝑡𝑉 𝑜𝑢𝑡𝑛𝑒𝑡 =The net inflow/ outflow from the unit which is the resultant of base flow, evapotranspiration losses, leakage from or to the deeper aquifers, net flow across the boundaries etc

Source -Assessment of Ground Water Resources : A Review of International PracticesRana Chatterjee, Scientist ‘D’ Ranjan Kumar Ray, Scientist ‘C’

BUT Why do we study water balance , development and management of groundwater resources?

Methodology The methodology used for estimating the annual replenishable groundwater resources is known as Groundwater resources estimation methodology—1997(GEC-1997), involves estimation of annual groundwater recharge from rainfall and other sources including irrigation, water bodies and artificial recharge and determination of present status of groundwater utilization.(Recommended by government of India for all states and Union territories)

Groundwater recharge estimation in GEC-1997 is computed season-wise(i.e. monsoon and non-monsoon season)

Source:- Dynamic groundwater resources of National Capital Territory, Delhi: assessment, development and management options Rana Chatterjee ,B. K. Gupta , S. K. Mohiddin

P. N. Singh ,Shashank Shekhar , Rajaram Purohit

NON MONSOON

SEASON

MONSOON SEASON

Water level fluctuation method (WLF) and empirical norms are used

FOR RECHARGE ESTIMATION THE FOLLOWING METHODS ARE USED.

Empirical norms

Total annual recharge =Recharge in monsoon season (from rainfall + other sources)+ Recharge in non-monsoon season (from rainfall +

other sources)

Source :- 1) Hydrology and Water Resource Of India by Sharad K. Jain, Puspendra K. Agarwal and Vijay P. Singh2) Dynamic groundwater resources of National Capital Territory, Delhi: assessment, development and management options

Rana Chatterjee ,B. K. Gupta , S. K. Mohiddin P. N. Singh ,Shashank Shekhar , Rajaram Purohit

Recharge (R) = Sy(dh/dt)(Scalnon et al: 2002; Healy and Cook 2002)

where Sy is specific yield, h is water table height and t is time

Considering the heterogeneity of the hydrogeological setup and complexities in the GW flow hydrodynamics, the estimations using GEC-1997 should be followed by micro-level studies before a large scale GW management plan is contemplated.

Recharge estimation using GEC-1997

Estimation of recharge involves following steps:

1.Work out recharge during monsoon season (July to October) using WLF method

----------------------------------- (2)R= h X Sy X A + DG

Where,R= possible recharge, which is gross recharge minus the natural discharges in the area in the monsoon season (hectare metre)H= WLF between pre-monsoon (May) and postmonsoon (November)A= area of computation of recharge (hectare)Sy= specific yieldDG= groundwater draft during monsoon season (hectare metre)



2.Segregate the resultant recharge [arrived at Eq. (2)] into recharge from rainfall and recharge from other sources.



------------

Where,RMrfi = recharge from rainfall during monsoon for the ith particular yearRMc= recharge due to seepage from canals during monsoon for the ith particular yearRMsw =recharge from surface irrigation during monsoon for the ith particular yearRMt =recharge from storage tanks and ponds during monsoon for the ith particular yearRMgw =recharge from groundwater irrigation during monsoon for the ith particular yearRMwc =recharge from water conservation structure during monsoon for the ith particular year

3. Normalize rainfall recharge for estimating recharge corresponding to the normal monsoon rainfall.

This was done in order to neutralize the effect of excessive or less than average rainfall on groundwater recharge estimation of a particular year.



------------

WhereRMrf (normal)= normal monsoon rainfall rechargeRMrfi =monsoon rainfall recharge for the ith particular yearr (normal)= normal monsoon rainfallri =monsoon rainfall of the ith particularyear



4. Compute rainfall recharge using RIF

Where, f is RIF and,

----------------

A =area of computation of recharge (hectare) and rM normal rainfall in monsoon season (metre)

5. Compare the rainfall recharge figure arrived at Eq. (4) [RMrf (WLF)] with rainfall recharge figures using RIF [RMrf (RIF)] for normal monsoon rainfall arrived atEq. (5).

PD Difference in WLF & RIF estimate expressed as a percentage of RIF estimateIf,a) if PD is within ±20%, RMrf = RMrf (WLF)b) if PD is<-20%, RMrf = 0.8xRMrf (RIF)c) if PD is>20%, RMrf = 1.2xRMrf (RIF)

-------------------------



6. Work out the total normal recharge during monsoon period.

------------------

----------------

7. Work out the normal rainfall recharge during non monsoon period (November to June of Next year) using RIF.

8. Compute recharge from other sources during non monsoon season.

9. Work out total recharge during non-monsoon season.

----------

----------



10. Annual replenishable groundwater resource is the sum total of monsoon and non-monsoon recharge.

----------

11. Deduct the allocation for natural discharge from replenishable resource to obtain net groundwater availability for utilization.

Net annual groundwater availability = annual replenishable groundwater resource - allocation from natural discharge during non monsoon season

Groundwater budgeting

In order to assess the status of utilization of groundwater resources in an assessment unit, the annual groundwater draft for irrigation, domestic and industrial uses are estimated. The percentage of annual groundwater draft for all uses to the Net annual groundwater availability gives the stage of groundwater development.Stage of groundwater development = 100*(annual groundwater draft/ net annual groundwater availability )

Stage of Groundwater Development

Annual Replenishable GW-432.72 BCM

45%

Natural Discharge- 34.6 BCM4%

Remaining26%

Irrigation - 222.36 BCM23%

Domestic and Industrial use- 22.71 BCM

2%Units in BCM

STAGE OF GROUND WATER DEVELOPMENT = 62% (AS ON MARCH 30TH, 2011)

Data Source : Dynamics GW Resource 2011( CGWB, 2014) Source- Dynamic GW resource -2011, Ministry of earth sciences,1997

Values in meter

Categorization Of The Sub-UnitStage Of Ground Water

Development (%)Ground Water Level trend Category

<=70 Either Pre-monsoon or Post Monsoon Water levels does not show a Falling Trend

SAFE

70-90 Both the trends during Pre and Post Monsoon Seasons do not show a Falling Trend

SAFE

70-90 Either Pre Monsoon or Post Monsoon water levels shows a Failing Trend

SEMI-CRITICAL

>90 Either Pre-monsoon or Post Monsoon Water levels Shows a Falling Trend

CRITICAL

<100 Both the trends during Pre and Post Monsoon Seasons show a Falling Trend

CRITICAL

>100 Both the trends during Pre and Post Monsoon Seasons show a Falling Trend

OVER- EXPLOITED

Source:- GROUND WATER RESOURCES ESTIMATION USING GEC-1997 METHODOLOGY By A.V.S.S.Anand Scientist, Central Ground Water Board Visakhapatnam

Categorization of Sub-Units

69%11%

3%16%

1%

TOTAL UNITS = 6607, AS ON MARCH,2011

SAFE- 4530 SEMI-CRITICAL- 697

CRITICAL - 217 OVER EXPLOITATION- 1071

Saline-92

SAFE

SEMI C

RITICAL

CRITICAL

OVER- EXPLO

ITED

SALIN

E0

1000

2000

3000

4000

5000

AS ON MARCH,2009

AS ON MARCH,2011

LegendsN

o of

ass

esse

d un

its

Data Source : Dynamics GW Resource 2011( CGWB, 2014)

North East states are in safe category Punjab , Haryana, Delhi, Rajasthan have around 75% over-exploited unitsUttarakhand ranks top in having highest no of semicritial units

Depth to water Level and Distribution of Percentage of Wells for the Period – Pre Monsoon and Post-Monsoon

0-2 mbgl 2-5 mbgl 5-10 mbgl 10-20 mbgl 20-40

mbgl >40 mbgl

05

1015202530354045

4.21

24.67

41.03

23.21

5.241.64

34.7230.82

19.38

10.1

3.281.69

Pre-Monsoon (total wells-12,492) Post-Monsoon (total wells-12,673)

Data Source:- GROUND WATER YEAR BOOK- INDIA 2013-14, CGWB, MOWS,GOI, JULY 2014

Perc

enta

ge

Recommended norms for the Assessment of Recharges fromOther Sources

Parameters Sources ofRecharge

Range of Parameters

Canal seepage factor Unlined canals 15 to 30 ham/day/million sq.m. of wetted area

Lined canals & canals in hard rock terrain

20% of above value suggested for unlined canals

Return flow factor Surface waterIrrigation

0.10 – 0.50*

Ground waterIrrigation

0.05 – 0.45*

Source :1) Dynamic GW resource -2011, Ministry of earth sciences,1997 2)Dynamic groundwater resources of National Capital Territory, Delhi: assessment, development and management options

Rana Chatterjee ,B. K. Gupta , S. K. Mohiddin P. N. Singh ,Shashank Shekhar , Rajaram Purohit

Water bodies(tanks and ponds) 0.00144 m/day/ha of water spread area

Water conservation structures 50% of the Gross Storage#

*Paddy : 20–50% of irrigation water, and Wheat, fruits/ vegetables: 5–30% of irrigation water#Out of this,50% is during monsoon season and the remaining 50% during non-monsoon season

CASE STUDY

Dynamic groundwater resources of National Capital Territory, Delhi: assessment, development and management options Rana Chatterjee , B. K. Gupta ,S. K. Mohiddin , P. N. Singh, Shashank Shekhar , Rajaram Purohit

INTRODUCTIONLatitude - 28024’15’’ and 28053’00’’ NLongitudes: 78050’24’’ and 77020’30’’ E

Area of NCT of Delhi- 1483 Sq. Km.

Population- 9.879 million(2011)

Average Annual rainfall: 611.8 mm

Divided into 9 districts

Annual Ground Water Draft- 1435 MCM

Bounded by the Gangetic alluvial plainin the north and east, the Thar desert in the west and Aravalli hill ranges to the South.

Covered with alluvium deposits occasionally traversed by linearly elongated quartzite ridges.

Hydrogeological map of National Capital Territory of Delhi

Thickness of alluvium has been recorded up to 300 m depth.

Itconsist of alternate layers of silt, clay, sand and Kankar

The major water bearing horizon is fine to coarse grained sand with Kankar.

Occurrence of sandy zonesdecrease with depth.

The thickness of fresh waterzone varies from 30 to 85 m. Transmissivity of the Older alluvial formation varies from 1 to 134 m2/day.

Transmissivity of the aquifer system of Younger alluvium varies between 730 and 2,100 m2/day

Data Source:- GROUND WATER YEAR BOOK- INDIA 2014-2015, CGWB,

Groundwater withdrawal pattern

Groundwater is predominantly being extracted for drinking and domestic purposes by the civic authorities namely Delhi Jal Board for city water supply and also by private individuals. Tubewells and handpumps are favourite modes of groundwater abstraction

Annual groundwater draft in NCT Delhi for 2004 has been estimated as 479.45 mcm, out of which 200.02 mcm (42%) is for irrigation purposes and 236.44 mcm (49%) is for domestic purpose. Groundwater withdrawal for industrialpurposes are comparatively less, about 43.00 mcm(9% of total groundwater draft) (CGWB 2006a).

Groundwater budgeting

The net annual groundwater availability is therefore 282 mcm. Since annual groundwater draft is around 480 mcm, the stage of groundwater development becomes 170%

Out of nine districts, seven districts are ‘over-exploited’ and two districts, i.e. North and Central are ‘safe’.

Hence, though at district level, seven out of nine districts in NCT Delhi are categorized as over exploited, micro-level studies have indicated that there are limited scope for ground water development in the Yamuna flood plain areas in NCT Delhi to meet the partial demand of domestic water. The underlying concept for groundwater utilization in Yamuna flood plain is that the flood waters which are available for short period of time during monsoon can be utilized for replenishment of de-saturated aquifers on account pre-monsoon groundwater withdrawal.

In the northern part of Yamuna flood plain in Palla well field in North Delhi (Fig. 11) 90 tube wells were constructed by Central Ground Water Board to augment the drinking water supply of NCT Delhi.

Depleting groundwater resources in the overexploited districts can be augmented through rainwater harvesting in the hydrogeologically suitable areas. Groundwater regulatory measures to be imposed in severely over-exploited areas through pro-active approach

Similar studies needs to be carried out in other areas within Yamuna flood plain for exploringthe scope for establishing additional well fields for augmenting the city’s water supply programme.

Groundwater development prospects in Yamuna flood plain

Image courtesy: www.banthebottle.net/articles/15-how-to-tips-to-conserving-water/

Thank You..!Source:- www.dropbydrop.eu/25571

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