Groundwater recharge in a limestone belt

The limestone belt of Jodhpur-Nagaur district of Rajasthan extends from Bilara (SE of Jodhpur) to

Rajdhal

Nimla

Bhadka

Nagurda JOgaSar Bheemda

BARMER SAMPLES

Ratari

Mahabar

SPsinghh

Mahabar

SPsinghh

o

TW/'87

DW/'87

*

TW/'96

-A-

DW/'96

A

Ratari

■oBhiyar

Bhiyar

DKDhani

Bhiyar

DKDhani

Fig. 13. Plot of 14C versus S18O for all samples collected from Barmer area.

72» 15' 72*30' 72*45' 73*00' 73*15' 73*30' 73*45' 74*<OT 74*15'

Fig. 14. Sample location map in the limestone belt of Jodhpur-Nagaur district of Rajasthan.

72» 15' 72*30' 72*45' 73*00' 73*15' 73*30' 73*45' 74*<OT 74*15'

Fig. 14. Sample location map in the limestone belt of Jodhpur-Nagaur district of Rajasthan.

Phalodi (north of Jodhpur) shown in Figure 14. In the southern part of the study area a controlling fault has channelized the flow of groundwater in the cavernous and fractured limestone. Caverns are widespread and have large dimensions in some parts, and are the source of copious ground-water. A number of tube wells are located in Ransi-gaon, which supply water to Jodhpur town. Groundwater contours in the area in April (UNDP 1971) show that the general flow of groundwater is southwards in the dry season, and the controlling fault acts as a sump. Groundwater contours for October indicate that the recharge during and after the monsoon is temporarily from the Luni river, which is located in the southern parts of the area (i.e. the flow is northwards). The Tertiary alluvium to the east of the limestone area partially contributes groundwater inflow to the limestone aquifer. The main source of recharge to the limestone aquifer is rainfall falling within the drainage basin of the Luni river and its tributaries.

Groundwater samples were collected mainly from tube wells for environmental 3H and 14C analysis. The results obtained are presented in Table 2. The 3H results show that the tube well sample from Pichiyak (located in the southern part of the area) has high 3H of 10 TU showing modern recharge. The tube well is located near the Pichiyak lake which is fed by the Luni river, and hence lake water contribution to groundwater is possible. Other tube wells from Ransigaon, Borunda, Amba Jatan in the southern part and Jhu-janda, and Rol in the northerneastern part of the limestone belt show 3H contents of 2-4 TU, indicating some component of present-day recharge. Tube well samples from northern and northwestern parts such as Khimsar, Beraltal, Jakhan, Laxmanna-gar, Moriya, Phalodi and Choti Benti show negligible 3H, indicating absence of modern recharge.

The 3H data of samples collected in 1992 for Borunda, Gotan, and Khimsaar are lower than those collected in 1990. This may be due to over-exploitation of groundwaters in the Borunda area leading to the influx of older waters from the neighbouring areas.

Model 14C ages (Pearson's model) are also given in Table 2. In Ransigaon and Borunda in the southern part, 14C data show that they represent waters younger than 1000 years. Recent waters are also found in the northern parts at Jhujanda and Rol. In Phalodi area the groundwaters are old with 14C ages in the range of 2500-4000 years. These groundwaters were probably recharged during the last pluvial episode. The 14C ages of the groundwater in Beratal and Jakhan in the central part are 1750 and 1900 years, respectively, and the 3H content is about 1.1 TU, suggesting that they are a mixture of young and old waters (Nair et al. 1993).

It may thus be concluded that modern recharge to the groundwater in the limestone belt occurs mostly from the southern parts. In the Phalodi area, the groundwaters are about 2500-4000 years old and were probably recharged during a pluvial period in the past.

Thus isotope techniques are useful in understanding groundwater recharge processes in arid

Table 2. 3H and I4C data of groundwater samples collected from the limestone belt (Jodhpur - Nagaur)

Location

Date sampled

3H (TU) ( + 0.5)

14C (PMC) (+1)

13C (%<,) ( + 0.2)

Age (years)

Pichiyak

August 1990

10.3

_

-

_

Ransigaon

August 1990

3.4

-

-

-

Borunda

August 1990

3.9

-

-

-

January 1992

2.8

64.6

-8.6

900

Hariadana

January 1992

1.9

60.1

-9.7

2400

Amba Jatan

August 1990

2.7

-

-

-

Gotan

August 1990 January 1992

1.5 0.5

-

-

-

Rampuria

January 1992

1.4

-

-

-

Asop

January 1992

1.0

-

-

-

Khimsar

November 1989

2.0

-

-

-

January 1992

1.0

50.7

-8.1

2400

Beratal

January 1992

1.1

54.3

-8.0

1750

Jhujanda

January 1992

3.3

82.9

- 10.0

Modern

Rol

January 1992

4.3

71.1

-9.5

900

Kapuria

November1989

2.0

-

-

-

Jakhan

April 1992

1.2

55.2

-8.3

1900

Laxmannagar

April 1992

0.5

45.5

-7.0

3100

Moriya

April 1992

0.8

54.6

-8.9

2500

Phalodi

November 1989

1.3

-

-

-

April 1992

1.2

54.8

-8.9

2500

Choti Bhenti

April 1992

0.5

44

-8.6

4000

areas. The absence of modern recharge and overexploitation of aquifers observed in some of the above studies stress the need for proper management of this scarce resource.

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