Date of Award

1-2005

Document Type

Thesis

Degree Name

Master of Science (MS)

Department

Civil and Environmental Engineering

First Advisor

Mohsen Sherif,

Second Advisor

Warren W. Wood

Third Advisor

Dr. Abdel-Mohsen Onsy Mohamed

Abstract

The UAE has achieved remarkable progress in transformation from separated small emirates to a modern union country with a high standard of living. The country is however, considered an extreme arid region.

In spite of these harsh conditions, The UAE government has encouraged plantation in towns, villages and country side. This has led to sharp increase in the agricultural sector particularly during the last three decades. As the irrigated land kept increasing, there was a deep concern about the water demand and the impact of agriculture activities on groundwater systems. Al-Khatim area is considered one of the most important agricultural areas in Abu-Dhabi emirate with 1300 farms covering an area of 2405 ha that has been affected by the decline in groundwater levels over the last years. Additionally the groundwater salinity has increased to 33,000 µS/cm in some places.

The main objective of this study is to assess the quantity and quality of groundwater in AL-Khatim area as an example of the effect of groundwater pumping and agriculture activities on the shallow aquifer. To achieve this aim, previous studies and investigations were reviewed. The required information and data about geology, hydrology, hydrogeology, and hydrochemistry were gathered and several tests have been conducted to evaluate the groundwater conditions in Al-Khatim area.

Well lithologies were drawn using Ground Water software for Windows (GWW) program from 19 newly drilled wells. From these wells several cross sections were developed. The Digital Elevation Model (DEM), developed by USGS, was used to draw elevation map for the study area. Measurements of water depth throughout the study area were conducted which were then used to draw contour maps of water level. The contour maps of water levels were presented for the years 1997, 1999, 2002, and 2003 to elaborate the drop in the water levels over the time.

The shallow unconfined aquifer in the study area was investigated by applying 2 step drawdown tests and 42 continues pumping tests. All data collected from these tests were evaluated using GWW program. The Transitivity and Storability of the aquifer in the study area were evaluated.

Two 2D resistivity profiles were conducted and oriented along the strike direction to intersect the maximum possible number of geologic features: The subsurface profiles were evaluated using a single channel Memory Earth Resistivity and IP Meter. Each profile consisted of 36 electrodes spaced 10 m apart which penetrate to about 60m. Wenner array was used in this survey and apparent resistivity data were collected and inverted to create a model of subsurface resistivity that approximated the true subsurface resistivity distribution and displayed as a cross section. Geophysical data Interpretation was constrained with the available drilling and groundwater quality information.

Ground water-quality assessment in the study area was done by collecting 28 groundwater samples from different locations in the study area. The ground water samples were analyzed in Abu Dhabi Municipality laboratory to determine the concentration of major cations (Ca2+, Mg2+, Na+, K+), major anions (SO42-, Cl-, CO3-, HCO3-, NO3-), Total dissolved solids (TDS), Electrical conductivity (Ec) and pH. To follow the trend of each substance, contour maps for each element were prepared. Nitrate levels in the groundwater of Al-Khatim area were presented as it is considered the most common contaminant due to agricultural activities. In addition chemical analysis diagrams (Piper and Stiff), two hydro chemical profiles were developed. The chemical data of Al-Khatim groundwater gave an indication about the origin of the groundwater in the study area. WHO standards were used to determine the suitability of Al-Khatim groundwater for different purposes such as drinking and irrigation.

Groundwater flow model "MODFLOW" was used to simulate the groundwater conditions in Al-Khatim area. The study domain was discretized in to 129 columns and 69 rows. The modeled area was divided into two regions, the outside region with a course grid with cells of 250,000 m2 and the region of interest with a detailed grid where each grid cell has an area 10,000 m2. The period 1997-2002 was chosen as the calibration period until good match between the observed and simulated groundwater levels was obtained. The model was used to predict the hydraulic head and drawdown for the year 2010 assuming same groundwater extraction rates.

Utilization of the groundwater in Al-Khatim area should be rationalized to stop its deterioration. Extraction rates of the groundwater in Al-Khatim area should be reduced and controlled by the concerned authority. Increasing farmer's awareness about environmental impact of different agriculture practices on groundwater should be considered. Further development of the present numerical model might be essential to better simulate the groundwater sustainability.

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