1.1 Groundwater in Bari Doab
The alluvial sediments that comprise of the aquifer exhibit considerable heterogeneity both laterally and vertically. Despite this, it is broadly viewed that the aquifer behaves as a single contiguous, unconfined aquifer. The study of the lithologic logs of boreholes (180 to 300 m depth) and test wells (30 to 110 m depth) indicates that Bari Doab consists of unconsolidated sand, silt and silty clay, with variable amounts of cankers. The sands are principally grey or greyish-brown, fine to medium grained and sub-angular to sub-rounded. Very fine sand is common for most of the bores: finer grained deposits generally include sandy silt, silt and silty clay with appreciable amounts of canker and other concretionary material. Re- evaluation of the original data (WAPDA, 1980) and geological sections (Unites States Department of the Interior, 1967) suggests that in the area between Lahore and Okara, there is a moderately persistent and alternate layers of finer materials (clay, silt) of about 15-30 m thickness without any regularity or continuity, and that these finer materials are more prevalent towards the Balloki side i.e. head of the irrigation systems. The near surface layer of clay/silt, 6-15m thick, is also prominently evident. However, thick layers (40 m of very fine to medium sand) were also found at deeper depths of the Bari Doab aquifer. Within the Middle Zone, as represented by the cross section near Sahiwal, silt/clay layers tend to be thinner and distributed unevenly, both vertically and horizontally. More importantly, the section shows that the aquifer characteristics tend to be very much sandy towards Harrapa town. Also, detailed study of lithologic logs of boreholes of BARI DOAB have shown sandy aquifer without any marked clay lenses. The Lower Zone, as represented by the cross section near Mianchannun (Chichawatni to Khanewal), appears to be as described above, with a greater predominance of sand, and rare clay/silty materials. Except for a few local lenses, that too are a few feet thick, beds of hard rock, compact clay are rare in the area, rather beds of hard rock could not be found in BARI DOAB commands during 1954-62 test drillings. Gravels of hard rock are not found within the alluvium and coarse or very coarse sands are uncommon. According to pumping test results as reported by Bennett et al., (1967), lateral permeability results for the tests in and around the BARI DOAB area varies from 28.96 to 255.45 m/day with an average of 84.09 m/day for these test. Specific yield values as reported for four of these tests were 0.06 (Renala Khurd), 0.24 (Pakpattan), 0.04 (Harrapa) (however the value of 0.04 is very less to yield any groundwater in contrary to the wells installed in the area) and 0.31 (Arifwala) and vertical permeability values were 1.01, 3.95, 11.06 and 21.06 m/day, respectively for these four locations. Bennett (1967) has mentioned an average anisotropy ratio of 25 to 1, on whole Punjab basis.
The aquifer under Bari Doab irrigation system is characterized by its unconfined behaviour i.e. water is mostly derived from storage by drainage of pores. The watertable location in the aquifer is space and time dependent due to its unsteady state nature as result of varying recharge and discharge rates both with respect to location and time in the area. Most of the aquifer water is discharged by pumping out for irrigation and/or drinking in the area. Surface water is added to the unconfined aquifer through seepage from canals, watercourses and field irrigation losses or by surface infiltration due to rainfall events and rivers in the adjoining area.
The area is divided by partition in India and Pakistan. The area is a part of a vast stretch of alluvial deposits worked by the tributary rivers of the Indus. The parent material is of mixed calcareous alluvium derived from a variety of rocks during the Pleistocene period. The general slope of the area is mild towards the south-westerly direction with average slopes ranging from 1 in 4,000 to 1 in 10,000. The area lies in the Bari Doab between Rivers Ravi and Sutlej. Agriculture in the area is sustained through surface water supplies and pumped groundwater. Extensive groundwater development facilitated the increase in cropping intensity by addressing shortages in canal supplies and also lowering the watertable which resulted in declining soil salinity in the area. It is estimated that about 50% of crop water requirements are met by groundwater extraction. Bari Doab is therefore a very good conjunctive use farming system.
According to post monsoon 2014 situation, more than 59.1% area of Bari Doab was having depth to watertable (DTW) below 12 m, another 27.3 % was having DTW between 6 to 12 m (Basharat and Basharat, 2019). Based on groundwater levels of 2002 and 2012, it was estimated that groundwater mining of 2.33 BCM (1.89 MAF) per year was taking place in Bari Doab (Basharat and Basharat, Basharat,2019). Thus, only 13.59% area of Bari Doab was in normal range of DTW (< 6m). Keeping in view the continuous depleting conditions in Bari Doab, drainage Section, IWASRI studied the feasibility of "Developing Sukh-Beas as Potential Recharge Site during Wet Years for Bari Doab". For recharging the Bari Doab aquifer, the proposal is to divert the flood water from the Balloki-Sulemanki (BS) and Sidhnai-Mailsi-Bahawal (SMB) Link canals into the Sukh-Beas channel, depending upon flood water availability in the river system and the carrying capacity of the channel itself (Basharat and basharat, 2019). According to past figures and current watertable contour map most of high watertable areas lie towards head-end except Lahore where watertable is deep due to pumping for water supply, as shown in Figure 1. This high or shallow watertable towards head-end is due to high rainfall in the area.
Figure 1: Depth to watertable map of Bari Doab for 2014.
1.2 Canal Water in Bari Doab
The most important and less dependable water resource is the canal water supply in the area. After the Indus Water Treaty in 1960 which gave India the water rights on the rivers Ravi, Beas and Sutlej, the Bari Doab falls under the Mangla Command receiving water through inter-river transfer links from the rivers Jhelum and Chenab, as shown partly in Figure 1 above. The irrigation water deliveries to the several canal commands in this large and complex national irrigation system are determined by the capacity of the physical infrastructure, i.e. reservoirs, barrages and inter-river link canals, as well as by legal agreements[1]/ and historic rules for the allocation of water. Cropping intensity in the Bari Doab area has steadily increased from the designed (60 percent) to the present about 200 percent. Canal supplies contribute up to 56 percent of the total supplies available at crop root zone. The other major contributor is the groundwater i.e. pumped by farmers themselves, however without any management by the government.
The groundwater supplies in many regions around the world are being rapidly reduced to meet growing irrigation demands and other needs in the face of diminishing surface water supplies e.g. USA and India (Rodel et al., 2009). The depletion of these groundwater supplies is expected to intensify as a result of climate change. These impacts are likely to be particularly severe in regions such as Bari Doab, where the groundwater is already being depleted at a very rapid rate. As the groundwater depletes the cost of pumping increases, and the risk of water quality deterioration also increases.
Nowadays, the potential of diverting surplus river flows has nearly been exhausted, and there are signs that surface water resource availability is dwindling, particularly in Bari Doab. This is due to decreasing online storage, population increase, and larger per capita water use with the passage of time. Until a few decades earlier, in addition to surface water utilization, increased groundwater use have provided a big boom for meeting additional water requirements. The exploitation of groundwater, mostly by private farmers, has brought numerous environmental and economic benefits to the agriculture sector in Pakistan. Share of groundwater is now almost half of all crop water requirements in the irrigated environment, at least in Punjab.
Groundwater is used for a variety of purposes in Pakistan, particularly including irrigation and drinking. A groundwater model is simplified representation of an actual groundwater system in the area. A range of computer codes (modeling software) exists for application to different problems. However, free software is only available from USGS in the form of MODFLOW and ModelMuse which is a Graphical User Interface (GUI) for MODFLOW.
1.3 STUDY AREA DESCRITION-CANAL COMMANDS:
This steady state groundwater model was developed in ModelMuse GUI developed by USGS, for irrigated areas of Bari Doab with a total area of 2.95657 Mha GCA. There are seven canal commands in the study are viz. Central Bari Doab Canal (CBDC), Lower Bari DOAB Canal (LBDC), Sidhnai, Depalpur Upper, Depalpur lower, Pakpattan and Mailsi as shown in the Figure 2 and Table 1 with salient features.
Table 1: Salient features of canal commands in BARI DOAB.
Canal
|
Year of Const.
|
CCA (000 ac)
|
GCA (000 ac)
|
Designed Intensity
|
Water Allowance
|
Discharge Capacity (000 cfs)
|
Length (Canal Miles)
|
Perennial
|
Non-Perennial
|
Perennial
|
Non-Perennial
|
Main
|
Total*
|
Lower Bari Doab
|
1913
|
1670
|
1789
|
60-67
|
66
|
3.00
|
3.30
|
9.20
|
129.90
|
1522.00
|
CBDC
|
1859
|
659
|
709
|
75-100
|
|
3.22
|
|
2.50
|
|
804.60
|
Upper Depalpur
|
1928
|
350
|
384
|
|
60
|
|
5.50
|
2.40
|
52.90
|
481.20
|
Pakpattan
|
1927
|
1049
|
1177
|
54-60
|
70
|
3.60
|
5.50
|
5.20
|
183.10
|
1143.20
|
Lower Depalpur
|
1928
|
612
|
654
|
|
60
|
|
5.50
|
4.00
|
6.40
|
779.00
|
Sidhnai Canal
|
1886
|
1017
|
1166
|
60-80
|
60
|
3.00
|
4.80
|
5.20
|
36.40
|
1145.20
|
Mailsi
|
data not available
|
|
|
|
|
|
|
|
Figure 2: Assumed HSUs and canal commands in Bari Doab.
In each HSU meteorological & hydrological parameters were assumed to be uniform for the development of MODFLOW Model. All the geographical features were digitized using geographic coordinate system (WGS-1984) in ArcGIS using Google Earth, which were subsequently transformed to the projected coordinate system (Kalianpur India Zone I, 1962) for calculations of areas and other linear measurements.
The study area has associated limitations e.g., there is not any comprehensive data regarding aquifer characteristics, groundwater availability and irrigation water use by the farmers in such a big area; except poor estimation of annual groundwater pumping for agriculture purposes only by NESPAK (2005) and Basharat (2012) for LBDC only. The study is based mostly on data collected from secondary sources e.g. aquifer characteristics, groundwater depth, and annual average irrigation supplies for last 10 years in canals.
1.4 Groundwater Modeling
Groundwater modelling is a helpful tool that can help analyze many groundwater problems in the area of interest. It begins with a conceptual understanding of the physical groundwater problem. The next- step in modelling is translating the physical system into mathematical terms. In general, the final results are the familiar groundwater flow and transport equations. These equations, however, are often simplified, using site-specific assumptions, to form a variety of equation subsets. An understanding of these equations and their associated boundary and initial conditions are necessary before a modelling problem can be formulated. This is also called conceptual model for the area.
Groundwater modeling, also called numerical modelling is a powerful tool to solve groundwater flow problems under varied and complex hydrogeological conditions and non-uniform recharge and discharge stresses. The flow domain is discretized into cells, nodes, and elements. The basic governing partial differential equation is transformed into a difference equation and applied recursively over the model domain. This results in a set of simultaneous linear equations which are solved with appropriate numerical analysis techniques e.g. using MODFLOW.
1.4.1 Finite Difference Method:
There are basically two distinct forms for numerical modeling: Finite Difference Method (FDM) and Finite Element Method (FEM). ModelMuse uses FDM approach for discretization of area. Both of these numerical modeling approaches require that the aquifer be discretized into a grid and analyzing the flows associated within a single zone of the aquifer or nodal grid of the model. Finite difference methods convert ordinary partial differential (PDE) equations, which may not be necessarily linear, into a system of linear equations that can be answered by matrix formation. Modern computers can perform these linear algebra operations efficiently, which along with their relative luxury of implementation, has led to the widespread use of FDM in modern numerical analysis. Today, FDM are one of the greatest common tactics to deal with the numerical answer of PDE.
1.4.2 MODFLOW:
Groundwater modeling by using computer / numerical approach have become a widespread tool for analyzing various groundwater issues in the area of interest. Thus, much commercial software has become available in the industry. USGS had developed a modular groundwater modeling package in FORTRAN language under the name MODFLOW. The pre- and post-processors has made the software more user friendly, thus inducing a tremendous boost to the utility and adoption of the MODFLOW package. The USGS original software i.e. MODFLOW is a public domain now and have become the industry standard, while most commercial software in the form of GUI for application of MODFLOW model are licensed and available at a cost from various vendors. These commercial software differ mostly in the pre-and post-processing of the data capabilities for the MODFLOW model application.
1.5 Graphical User Interface
A number of the codes have Graphical user interfaces (GUIs), which help for MODFLOW in the creation of input files for the model code to read and for visualization of the model output. As a matter of fact, the basic concept of all models e.g. Visual MODFLOW, Groundwater Vistas, GMS, PMWIN is the same. There is no significant difference between them except software environment. ModelMuse is also the pre and post-processing platform developed by the USGS that implements MODFLOW model. However, this platform has a high performance due to its "design by objects" that optimizes the conceptualization of boundary conditions and other elements of the model, reducing the time needed to build the model and improving the interpretation of the output data of the area.
[1]/Water Accord, March 1991.