Investigating the infiltration of saline water from Chah Jam desert to Damghan plain aquifer in Semnan province

Master's Thesis in Water Engineering - Water Resources Management

Abstract

The advance of salt water in fresh water aquifers is not limited to the islands and coasts of oceans, seas and salt lakes, but it is possible for salt water aquifers to advance through deserts, swamps and salt water pits in the adjacent fresh water aquifers, making it salty and unusable in critical conditions. Due to its dry climate, Iran has abundant deserts. Limitation of surface water sources and excessive exploitation of underground water has caused salt water to advance to fresh water aquifer in the border areas of the desert.

According to the statistics and information of the Semnan Regional Water Organization from Damghan plain, the quality of drinking and agricultural water in the villages in the northeast of the plain has decreased due to the infiltration of salt water from the Chah Jam desert, and [1] TDS observed in some villages is about 7000 milligrams per liter. reached and the continuation of this trend can lead to the advance of salinity towards the city of Damghan and the agricultural sector of the region, therefore, in order to provide a perspective of the future situation of this plain in case of continuing the current process of extracting underground water or reducing and increasing pumping, modeling of the plain was done and the future state of the plain in terms of the drop in the level of underground water and the level of salinity was predicted with the assumption of three scenarios. 3D simulation is placed. In order to predict the condition of the aquifer in 2015, the information of a 5-year period of quantitative and qualitative observation wells for the years 2016 to 2018 was recalibrated and verified for two years 2018 and 2019. The results showed that with the continuation of the current draining and feeding process, in 2015 the underground water level will drop the most by 16 meters in the western area of ??Damghan city and the salt concentration in quality wells will increase by an average of 150 mg/liter. Also, reducing the pumping of exploitation wells by 15% will cause the water level to drop by 14 meters and slow down the advance of salt water in the plain aquifer and increase the salt concentration by 82 mg/liter, which is 45% less compared to the assumption of continuing the current trend. On the other hand, increasing the pumping of exploitation wells by 15% will result in a drop in the water level of the aquifer by 20 meters and an increase in the average salt concentration by 464 mg/liter.

Key words: Groundwater, saltwater advance, interaction of saltwater and fresh water, Damghan Plain aquifer, modeling, simulation, Visual Modflow

Chapter 1

General

1-1 Introduction

About 97% of the total water on the planet is in the seas and oceans, whose salinity is high and cannot be used by humans under normal conditions. Another two percent is in the form of polar ice, which cannot be used in the current conditions. Most of the remaining one percent, which is fresh, is made up of underground water (Figure 1-1). With the expansion of settlements in areas where there is no surface water or its amount is low, the use of underground water resources as a safe alternative has been considered, so that in some areas, underground water is considered as the only source of water supply.

(Images are available in the main file)

The population growth and development of human societies has led to the demand for more water consumption, and due to the approximate stability of water supply sources, it should be managed with Sahih kept supply and demand in balance. This makes it necessary to protect water resources against pollutants (infiltration of salt water and other chemicals). The population concentration in the coastal areas and of course the growth of activities has caused an increase in the amount of groundwater withdrawal. This increase in harvesting has caused the movement of salty sea water towards the aquifers, and this has resulted in more salinity of these resources.

High salinity (more than 2 to 3%) makes it impossible to use water for drinking, and this problem must be overcome by processes such as purification or mixing with fresh water. Therefore, the protection of underground water resources is a fundamental issue in the conditions of increasing demand and decreasing these resources.

In most parts of the country, especially in areas where surface water does not exist, or is not permanent or exists in small amounts, the water needed by cities, industries, villages and livestock farms is supplied from underground sources. Even in places where rainfall is high and the weather is humid, such as Gilan and Mazandaran, where there is surface water and they are among the rainiest places in Iran.In order to achieve high production in agriculture and to compensate for the lack of required water, underground water is also used. In almost all cities of Iran, due to the lack or lack of surface water or because it is polluted, underground water is also used [9]. This issue has attracted attention in many countries that have coasts. Investigating the phenomenon of the inflow of saline water from Chahe Jam to Damghan plain aquifer is the main goal of this thesis.

In this thesis, an attempt has been made to investigate the possibility of the advance of saline water from the desert side to Damghan plain

regarding the beginning of the project period, and according to the existing conditions, the future has been predicted. Using the VISUAL MODFLOW software and the SEAWAT package, the saltwater advance is modeled. The conditions at the beginning of the project period are entered into the model as input data, and after the model is recalibrated, the saltwater advance is predicted for 10 years after the beginning of the project period, according to 3 hypothetical scenarios. 1-3 basic research questions. With the continuation of the current situation, How will the water level drop and salt concentration change in Damghan Plain?

With the successful implementation of management policies and reducing pumping by 15%, how will the water level drop and salt concentration change?  

If pumping is increased by 15% (which is the most likely assumption), how will the drop in water level and salt concentration in the plain change?

1-4 research assumptions

Based on available sources, during this research, assumptions have been made that in terms of physical characteristics, according to the report of the Semnan Province Regional Water Corporation regarding the plain, the aquifer of this plain is a three-layer free aquifer, and this free aquifer is in the The second and third are located. The storage coefficient (S) in the whole plain is 4% and the hydraulic conductivity coefficient (K) is assumed to be a constant value for each layer. Each aquifer layer is homogeneous and the density depends only on the salt concentration and other influencing factors are ignored. According to the data of the regional water joint stock company, statistics of pumping wells, and annual quantitative and qualitative observation wells were considered. In addition, the balance calculated by the Regional Water Organization of Semnan province was used. According to the balance calculations of this organization, the discharge of the spring in the water year of 85-86 was zero and the discharge of the aqueduct was about 2 million cubic meters per year, which is a small amount compared to the total discharge from the aquifer of 160 million cubic meters. Therefore, the effect of spring and aqueduct in Bilan was assumed to be zero.

1-5 reasons for using underground water

The advantages and advantages of underground water compared to surface water have caused the developed countries of the world to put more effort into providing drinking and consumption water in their urban and industrial areas from underground water.

On the other hand, the high consumption of underground water has caused that in many parts of the world, including the country The level of the underground water table will drop drastically, many aqueducts and other water sources will dry up, salt water will advance in the fresh underground water tables, and in the population and industrial centers, a significant part of the underground water will be polluted. Compared to surface water, it is less contaminated with microbes, parasites and harmful substances.

In many dry and desert areas of our country, due to the lack of access to fresh surface water, underground water is the only usable source.

In many cases, the cost of extracting underground water is lower than obtaining water from surface sources.

The temperature of underground water is almost constant. Therefore, underground water has a great advantage as a coolant.

Underground water sources are much less affected by drought than surface water sources.

In many parts of the world, including many dry and desert parts of our country where there is no surface water, or it is not usable or reliable, underground water is the only source of water consumption and the lives of the residents and animals of these areas depend on this source. [9].

1-6 Groundwater Pollution

The quality of underground water is an important issue in the development and management of water resources.