PINSTECH/RIAD-132 ISOTOPIC STUDY OF WATERLOGGING AND SALINIZATION IN PESHWAR VALLEY R. M. QURESHI M. I. SAJJAD M. AHMED S. D. HUSSAIN M. A. TASNEEM P. FRITZ RADIATION AND ISOTOPE APPLICATIONS DIVISION Pakistan Institute of Nuclear Science & Technology P. O. Nilore, Islamabad April, 1992 PINSTBCH/RIAD-132 ISOTOPIC STUDY OF WATERLOGGING AND SALINIZATION IN PESHAWAR VALLEY R. M. QURE8HI M. I. 8AJJAD M. AHMED S. D. HUSSAIN M. A. TA8NEEM P. FRITZ * RADIATION AND ISOTOPE APPLICATION DIVISION PAKISTAN INSTITUTE OF NUCLEAR SCIENCE AND TECHNOLOGY P. O. NILORE, ISLAMABAD April, 1992 * Scientific Director General, Umwelt Forschungzentrum, Liepzig, F. R. Germany inil*n** .* f \ ABSTRACT A detailed account of the application of isotope and geochemical techniques in the study of waterlogging and salinization of agricultural lands in the Peshawar valley area is presented. Precipitation samples, surface/groundwater samples and aqueous sulphate were analysed for tritium and stable isotope ratios of hydrogen, oxygen and sulphur. The data show that the artesian aquifer is recharged by the precipitation at high mountains whereas local precipitation and irrigation canal waters are mainly responsible for the recharge and waterlogging in the unconfined aquifer. In some parts of the valley, upward leakage from artesian water is found to cause waterlogging. The valley area contains water recharged after 1953. The chemical quality of the shallow groundwater is quite poor as compared to that of deep groundwater. 1 "™^»! CONTENTS 1. INTRODUCTION 1 2. PROJECT AREA 1 3. ISOTOPIC AND HYDROCHEMICAL INVESTIGATIONS 3 3.1 FIELD AND LABORATORY METHODS 3 4. RESULTS AND DISCUSSION 4 4.1 ISOTOPE INPUT FUNCTIONS 4 4.2 ISOTOPIC COMPOSITION OF GROUNDWATER 5 4.2.1 SPATIAL DISTRIBUTION OF ISOTOPIC DATA 5 4.2.2 VERTICAL DISTRIBUTION OF ISOTOPIC DATA 6 4.2.3 RELATIVE CONTRIBUTIONS FROM DIFFERENT INPUT SOURCES 6 4.2.4 SULPHUR ISOTOPE COMPOSITION OF SULPHATE 7 4.2.4.1 34S INSULPHATES OF SOIL CORES 8 4.3 CHEMICAL QUALITY OF SURFACE AND SUB-SURFACE WATERS 8 5. CONCLUSIONS 9 6. REFERENCES 10 ISOTOPIC STODY OF WATERLOGGING AND 8ALINIZATION IN THE PESHAWAR VALLEY 1. Introduction A detailed account of the application of isotope and geochemical techniques in the study of waterlogging and salinization in the Peshawar valley is presented. Water samples from the irrigation canals, open wells and pumping wells were analyzed for tritium and stable isotope ratios of hydrogen and oxygen. Aqueous sulfate from water samples and sulfate (soluble as well as adsorbed)extracted from the soil cores were also analyzed for £3AS. In addition, precipitation samples have been collected to determine the isotopic index of rain water. These analyses were used to determine : a) the potential sources of recharge in the shallow unconfined aquifer and the artesian aquifer, and b) the extent of mixed waters in the Peshawar valley in terms of effects on the chemical quality of shallow groundwaters. 2. Project Area The Peshawar Valley with a gross area of 911 square kilometer (of which 773 square kilometer are culturable) is situated between longitutdes 7l°-23' to 71°-55'E and latitudes 33°-50 to 34°-10'N (figure 1). The area has a subtropical and semi-arid climate. Summers are hot and dry in June and and very humid in July and August. Winters are relatively cold with light frost in December and January. The mean monthly maximum and minimum temperatures range from 17-40 °C and 4-26 °C respectively. The average annual precipitation amounts to about 380 mm. The Peshawar valley is tectonically unstable and has many faults and folds. The mountain ranges bordering the valley area on the west, southwest and southeast consist of a complex and highly indurated and structurally deformed sedimentary and metamorphic rocks ranging in age from Precambrian to Tertiary. The extension of these mountains form the bed rock under the alluvium of the valley area. Simultaneous deposition of the alluvium and erosion gradually changed the land surface. The land altitude varies from 290 m to 442 m above the mean sea level with a general slope of 3 m per kilometer towards north-east. Hydrologic characteristics of the sediments in the valley were obtained by the Water and Soil Investigations Division (WASID) of the Water & Power Development Authority (WAPDA). The average porosity determined from the repacked drill cuttings is about 42.4 percent. Groundwater in the valley mainly occurs in the alluvial deposits of quarternary age. The rocks on 1 the west, southwest and south form the impermeable boundary of the groundwater reservoir. The groundwater occurs under water table conditions and also under artesian conditions. The general movement of the groundwater is from the southwest towards the river Kabul. The exact extent of the artesian zones is not yet defined and it appears to extend from the Khyber hills towards the city of Peshawar where it has been observed at shallow depths of 15 m [WAPDA, 1973]. History of canal irrigation in the valley dates back to some 300 years - the time of Moghul Emperor Aurangzeb. Regulated canal system came into being with the construction of the Kabul river canal in 1893 and with the development of Warsak Dam high level canal system (Gravity flow canal and the Lift canal). Several small inundation channels known as Kaphas offtake from the Kabul and the Bara rivers. Also, the valley is traversed by numerous torrents locally known as Khawars coming down from the hill ranges in the south and southwest. In the Peshawar valley, the geological formations contain extensive clayey deposits with shingle beds, silt and clayey stratifications. The sandy beds in the area are also not as much water yielding as under the Indus plains. The water table and soil salinity levels of the valley have been continuously increasing since the development of canal irrigation system. This irrigation scheme has resulted in the rise of water table within a meter or so of the general land surface in some parts of the irrigated areas of the valley alongwith the development of soil salinity which retards the crop growth considerably. According to a study by WASID the water table was rising by 1.5-2.5 m per year adjacent to the Warsak canal system. Nearly 10 percent (91 square km ) of the area was affected by salinity of which 4.1 percent was severely saline. Since 1979-80, WAPDA installed more than 200 pumping wells (tube wells) and a number of dug wells in the area, under the SCARP program to pump groundwater continuously from depths of 15-60 meter in order to decrease the water table [WAPDA,1973]. However, the water table has not significantly dropped and a considerable portion of the valley still shows patches of surface water. A number of open wells in the area show water table 1 meter below general land surface. A number of tube wells are flowing under artesian conditions. Although the surface salts have been washed down at many places due to the recycling of canal-fed irrigation waters, the SCARP programme, in general, has not yet resulted in a perma­ nent solution to the problem [Mushtaq, 1985]. In many areas, the continuous pumping by the tube wells has not proved efficient in lowering the water table and the salts reappear on surface in the early winter season. Previous studies by the WAPDA indicated that a major emphasis was given to the physical hydrology of the Kabul river basin for water resources development for agricultural purposes and no particular attempt was made to look at the origin of salinity and the long term consequences of the 2 extensive unlined canal irrigation practices towards waterlogging. In this report an attempt is made to utilize i sot ope- geochemical techniques in order to identify various hydrological and hydrogeochemical features developed after the completion of SCARP programme in the Peshawar valley. 3. Isotopic and Hydrochemical Investigations 3.1 Field and Laboratory Methods a) Water Samples: Figure 2 shows the location of sampling points in. the Peshawar valley. Water samples from open wells, pumping wells (tube wells) and irrigation canals were collected on quarterly basis. Only those open wells were sampled which are frequently used by the local population for drinking/irrigation purposes. Canal samples were taken at specific locations during each sampling trip. All water samples were collected in doubly stoppered bottles to avoid evaporation losses. These samples were used for isotopic and chemical analyses. pH, EC and temperature of all samples were measured in the field. Aqueous sulphate was precipitated in the field as barium sulphate by the addition of barium chloride in mildly alkaline water samples. Precipitation samples after each rain event were collected at a permanent station located in the Peshawar city. Due to the sensitive nature of the area it was not possible to install a proper meteorological station in the mountainous areas. Therefore, all the isotopic data for precipitation correspond to the single sampling station. Precipitation samples were collected with a simple funnel-and-bottle arrangement. 180,2H,3H in water molecules and all hydrochemical analyses were performed in the Isotope Hydrology Laboratories at PINSTECH. All stable isotope analyses are expressed in the conventional s%o(delta per mil) notation and referred to the standard SMOW (Standard Mean Ocean Water) for all 180, 2H analyses and to CDT (Canon Diablo Troilite) for all 3t,S analyses of sulphate. Measurements of standards and samples indicate the overall analytical error below + 0.1 %o for 180 and ± 1 %o for ZH in case of water samples. 34S composition of the aqueous sulphate was performed at the Isotope Geochemistry Laboratory, Department of Earth Sciences, University of Waterloo, Canada. Measurements of sulfate standards and samples indicate the overall analytical error below ± 0.3 %o for3 *S.