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North Central Chhattisgarh Region
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|GROUND WATER RESOURCES|
The state of Chhattisgarh has been divided into 16 districts and 146 blocks. Ground water resources of all the 146 blocks of Chhattisgarh were assessed based on GEC’84 methodology by Central Ground Water Board, North Central Region, Bhopal and State Ground Water Survey Department, Madhya Pradesh in 1994. Later, the draft figures were modified by Central Ground Water Board, NCCR, Raipur in the year 1998 based on the data made available by the state agencies. Groundwater resources of the state were again estimated for the year 2001-02, based on the revised methodology (GEC’97). Recently as per the recommendations of the standing Committee on R&D Advisory Committee for ground water resource estimation, ground water resources were projected to 31st March 2004 and the units were categorised as per the modified set of criteria. Information in this page are related to availability of resources and status of groundwater development in the state as on 31st March 2004.
State Level Committee
Estimation of Ground Water Resources has been carried out based on the methodology recommended by the Ground water Estimation Committee (GEC’97). Salient features of the methodology and norms adopted in this report are given below:
Ground water year: The resource computations presented in this report is for the ground water year 2001-2002 (1st June 2001 to 31st May 2002). Chhattisgarh experiences rainfall caused by SW Monsoon, which generally commences by second week of June. The monsoon period has been taken as 4 months i.e. from June to September. Rest 8 months (October to May) have been considered as non-monsoon period.
Unit of computation: The unit of computation proposed in the methodology is ‘watershed’. However, it also recommends block/tehsil as the unit for the first few years since there can be non-availability of data. In the present report, block- the smallest administrative unit is taken as the unit of computation. This is manly due to lack of data especially on number of ground water structures, draft, population and other vital figures on watershed basis.
Sub-units: The following sub-units are recommended for the computation of various figures in the methodology and they have been considered as detailed below:
(a) Hilly areas: - Area with more than 20% slope have been excluded for the recharge computation.
(b) Poor ground water quality area: - There is no mapable area, which can be demarcated as poor ground water quality asaarea in the state and hence not considered.
(c) Command and non-command area: - The methodology envisages computation of various figures separately for command and non-command area. The data were made available by the State Ground Water Survey of Water Resources Department, Chhattisgarh and the same were utilized for computations.
(d) Lithological sub-units: For the computation of recharge and other figures the units were divided into sub-units as decided above to the extent possible. Afterwards the area underlain by various formations were demarcated and the areas were measured separately.
Gross ground water draft : Ground water draft for various uses in the different subunits have been estimated according to the recommended methodology. The details are given below:
(a) Domestic draft: Ground water draft for domestic use has been estimated based on block-wise population. The population figures of the 1991 census have been projected to the year of assessment considering the decadal growth rate since the block-wise population as on 2001 was not available. The average per capita consumption has been taken as 60 litres per day assuming 100% dependence on ground water. Draft during monsoon and non-monsoon periods have been estimated separately taking 4 months as monsoon period and 8 months as non-monsoon period as mentioned earlier.
The unit drafts mentioned above are for the non-command area. For command area, the unit drafts have been taken as 50% of above as the wells in these areas are utilised only as a supplement to other sources.
(c) Industrial draft: Ground water in the state is mostly used for domestic and irrigation purposes. Ground water draft for industrial use is negligible and has not been included while assessing the ground water draft.
Recharge from monsoon rainfall: Recharge from monsoon rainfall has been estimated separately for command and non-command areas.
Recharge has been computed using both water level fluctuation method as well as rainfall infiltration factor method. For comparison of figures obtained from the above two methods, percent deviation has been computed and the recharge has been calculated according to the recommended methodology.
(a) Recharge computation by water level fluctuation method: Recharge from rainfall using water level fluctuation has been estimated using the following relation
Rrf = S + D – Rother
Rrf = Recharge from Rainfall
S = Change in Storage (Area x Water Level Fluctuation x Specific Yield)
D = Gross Draft
Rother = Recharge from other sources
Rnrf = NMR x Rrf / AMR
Rnrf = Normalised Rainfall Recharge
NMR = Normal Monsoon Rainfall
Rrf = Computed Rainfall Recharge
AMR = Actual Monsoon Rainfall in the year of assessment
(b) Recharge computation by rainfall infiltration factor method: Rainfall recharge during monsoon as well as non-monsoon periods have been computed using, normal monsoon rainfall (data obtained from IMD), rainfall infiltration factors and area. The rainfall infiltration factors for different formations have been taken as those recommended by GEC’97. Major rock types of the state and the respective rainfall infiltration factors are given in the following table. The equation used for computation of recharge is
Rrf = NMR x A x RIF
Rrf = Recharge from Rainfall
NMR = Normal Monsoon Rainfall
A = Area of the unit/sub-unit
RIF = Rainfall Infiltration Factor
The results from the above two methods (water table fluctuation and rainfall infiltration method) have been compared using Percent Deviation using the following relation:
P.D. = 100 x (Rrfwtf – Rrfrif) / Rrfrif
P.D. = Percent Deviation
Rrfwtf = Recharge from Rainfall (Normalised) as computed by Water Table Fluctuation Method
Rrfrif = Recharge from rainfall as computed by Rainfall Infiltration Factor Method.
After the computation of the percent deviation the following criteria as recommended by the methodology (GEC’97) has been used to compute the Recharge from rainfall:
i) if – 20 ≤ P.D ≤ + 20 then Rrf = Rrfwtf
ii) if P.D. < – 20 then Rrf = 0.8 * Rrfrif
iii) if P.D. > 20 then Rrf = 1.2 * Rrfwtf
Recharge from rainfall during non-monsoon period: Recharge from rainfall during non-monsoon period has been computed by Rainfall Infiltration Factor Method as described above.
Total annual recharge: Total Annual Replenishable Resource was computed as arithmetic sum of recharge from rainfall and recharge from sources other than rainfall.
Net annual ground water availability: Net annual ground water availability has been computed by deducting the unaccounted natural discharge from the total annual recharge. Unaccounted natural discharge has been taken as 5 to 10% of the total annual recharge as per the criteria recommended by GEC’97.
i) 5 % : if the recharge from rainfall has been computed by water table fluctuation method
ii) 10% : if the recharge from rainfall has been computed by rainfall infiltration factor method
Stage of ground water development: Stage of ground water development has been computed using the relation:
Water table trend: Linear Regression analysis (separately for premonsoon and post monsoon periods) of Depth to Water Table data was carried out using NHNS data of one decade (1992-2001) with the help of GWDES. If the linear regression coefficient so computed was found to be < – 5 cm per year the water table trend was designated as rising and if the coefficient was found to be > +5 cm per year the trend was designated as falling. If the regression coefficient lied between –5 and +5 then it was taken that there is no change (neither rise nor fall) in water table.
Categorisation: The sub-units have been categorised into 4 categories SAFE, SEMICRITICAL, CRITICAL and OVER-EXPLOITED using the following criteria as recommended by GEC’97
SAFE: If the stage of ground water development is ≤ 70% and the water level during at least one of the two intervals (pre or post-monsoon) does not show a falling trend OR if the stage of ground water development is ≥ 70% but ≤ 90% and water level does not show a falling trend in any of the periods (pre or post-monsoon)
SEMI- CRITICAL: The stage of development is more than 70% but less than or equal to 90 % and water table during only one of the two intervals shows a falling trend.
CRITICAL: Stage of ground water development is more than 90% and the water table during only one of the two intervals shows a falling trend. OR stage of development is less than or equal to 100% and water table during both the intervals (pre and post-monsoon) shows falling trend.
OVER EXPLOITED: Stage of ground water development is more than 100% and the water table in both the intervals shows falling trend.
TO BE RE-ASSESSED: Recently, the R&D advisory Committee has suggested that if there is not an agreement between water level trends and stage of development, then the data are to be rechecked and the resources are to be re-assessed.
Allocation for domestic and industrial water supply: Allocation of ground water for domestic use has been estimated upto the year 2025 based on the projected population in 2025. The population figures have been projected using the 1991 census data and the decadal growth rate.
Net annual ground water availability for future use: Net ground water availability for future use has been computed using the relation
R = A – (B + C)
R = Net annual ground water available for future irrigation use
A = Net available ground water resource
B = Gross ground water draft for irrigation
C = Allocation for domestic and industrial water supply
Irrigation potential: Irrigation potential of ground water resources is the area that can be irrigated from available ground water resources.
According to Gec’97, stage of development below 70% is considered safe under all circumstances whereas stage of development upto 90% is considered safe if the long-term water levels do not show any declining trends.
In this report block-wise irrigation potentials have been computed considering both 70% and 90% of the available resources as exploitable within safe limits. Since the principal irrigated crop in the state is paddy, the irrigation potential have been computed considering the crop water requirement of paddy for Madhya Pradesh i.e. 0.694 m . This figure is as per the studies of Agricultural research station, Sehore under Jawaharlal Nehru Krishi Vishwa Vidyalay, Jabalpur (CGWB, 1992).
The computational procedure followed is given below.
1. Considering 70% stage of development
Pi = ((0.7 X Ra) – DGi – Dd2025) / D
2. Considering 90% stage of development
Pi = ((0.9 X Ra) – DGi – Dd2025) / D
3. Ultimate irrigation potential
Pi = Ra – Dd2025 / D
Pi = Irrigation potential in ha
Ra = Available ground water resources (Total Resources – Natural losses) in ha m
DGi = Gross ground water draft for irrigation in ha m
Dd2025 = Allocation for domestic and industrial use in the year 2025 in ha m
D = Crop water requirement in m (here it is 0.694 m)
Additional potential recharge: Additional Potential recharge is computed for water logged, shallow water table or flood prone areas. Since there is no such area of mappable scale in Chhattisgarh, additional potential recharge has not been taken into consideration.
Static ground water resource: Block-wise static ground water resources have been computed taking the maximum depth of water level fluctuation, permissible depth of mining, specific yield (Sy) and the area suitable for ground water recharge. Out of the entire thickness of the formation between the deepest level of water table fluctuation and permissible depth of mining, 2% has been considered as the total fracture zone. The specific yield values have been taken as weighted average of specific yield values for different formations. The formula used for the computations is as follows
Rs = A X Sy X Tf
Tf = (Z2 – Z1) X 0.02
Rs = Static ground water resources in ha m
A = Area in ha
Sy = Specific yield
Tf = Total thickness of the fracture zone
Z1 = Depth of maximum water level fluctuation in m
Z2 = Permissible depth of mining in m
Total recharge to ground water has several components, rainfall being the major one. Other components include seepage from canals, return flow from surface water irrigation, return flow from ground water irrigation, seepage from tanks and ponds etc. In Chhattisgarh, recharge from rainfall is of the order of 1.3 million ha m whereas that from other sources is 0.16 million ha m. Comparison of recharge from rainfall and recharge from sources other than rainfall shows that in most of the districts, the later accounts for less than 20% of the total recharge. However, in the districts like Bilaspur, Dhamtari, Durg and Janjgir-Champa, recharge from sources other than rainfall is as high as 40% of the total annual recharge. This is due to the fact that these districts practise intensive irrigation from surface water as well as ground water resources. Canal network in the above districts is also comparatively large. Due to the above reasons seepage from canal and return flow from irrigation becomes substantial in the above districts. Of the various sources other than rainfall, return flow from ground water irrigation accounts for 56%, return flow from surface water irrigation accounts for 32%, recharge from tanks and ponds accounts for 10% and seepage from canals accounts for 2%. Distict wise ground water recharge from rainfall and other sources are given in the following graph.
Gross ground water draft for all uses (Irrigation,Domestic and Industrial) in the state is 279532 ha m. with Durg having the highest (50792 ha m) and Dantewara having the lowest (4139 ha m). Durg is the most developed district in the state in terms of agricultural production and dependence on ground water is very high in the district. Comparison of ground water draft for various uses reveals that draft for irrigation accounts for more than 83 % of the total ground water draft, whereas draft for domestic purposes accounts for 17 % of the total ground water draft in the state. Ground water draft for industrial uses in the state is negligible.
Stage of groundwater development on an average is low in the state. Out of 146 blocks, 16 blocks (11%) have stage of development within 30 to 50 %, 16 blocks (11%) within 50 and 70 %. Only 8 blocks (5.5%) have attained stages of development more than 70%. Rest 106 (78%) blocks have stage of development within 30 %.The state as a whole has a stage of development of only 20.41%.Durg district has the highest average stage of development (65.4) and Dantewara district has the lowest (2.36%) Out of 146 blocks, 8 have been categorised as semi-critical from ground water development point of view. Caution should be exercised while planning groundwater development in these blocks. Out of these 8 blocks, 6 fall in Durg, 1 in Dhamtari and 1 in Bilaspur District. Rest 138 blocks have been categorised as safe from groundwater development point of view.
Blocks categorised as semicritical are shown in the following map.