Groundwater Hydrology

Engineering, Planning, and Management

Mohammad Karamouz, Azadeh Ahmadi, Masih Akhbari

• Editorial: CRC Press
• Año: 2020
• ISBN:
  9780429560682
• Edición: 2
• Categoría: Biological Sciences
• Categoría: Environmental Science

Increasing demand for water, higher standards of living, depletion of resources of acceptable quality, and excessive water pollution due to urban, agricultural, and industrial expansions have caused intense environmental, social, economic, and political predicaments. More frequent and severe floods and droughts have changed the resiliency and ability of water infrastructure systems to operate and provide services to the public. These concerns and issues have also changed the way we plan and manage our surface and groundwater resources. Groundwater Hydrology: Engineering, Planning, and Management, Second Edition presents a compilation of the state-of-the-art subjects and techniques in the education and practice of groundwater and describes them in a systematic and integrated fashion useful for undergraduate and graduate students and practitioners. This new edition features updated materials, computer codes, and case studies throughout.

Features:

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• Discusses groundwater hydrology, hydraulics, and basic laws of groundwater movement

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• Describes environmental water quality issues related to groundwater, aquifer restoration, and remediation techniques, as well as the impacts of climate change \

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• Examines the details of groundwater modeling and simulation of conceptual models

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• Applies systems analysis techniques in groundwater planning and management

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• Delineates the modeling and downscaling of climate change impacts on groundwater under the latest IPCC climate scenarios

Written for students as well as practicing water resource engineers, the book develops a system view of groundwater fundamentals and model-making techniques through the application of science, engineering, planning, and management principles. It discusses the classical issues in groundwater hydrology and hydraulics followed by coverage of water quality issues. It also introduces basic tools and decision-making techniques for future groundwater development activities, taking into account regional sustainability issues. The combined coverage of engineering and planning tools and techniques, as well as specific challenges for restoration and remediation of polluted aquifers sets this book apart.

1	Introduction

1.1 INTRODUCTION

Increasing demand for water, higher standards of living, depletion of resources of acceptable quality, and excessive water pollution due to urban, agricultural, and industrial expansions have caused intensive environmental, social, and political predicaments. In the last century, the population of the world has tripled, nonrenewable energy consumption has increased by a factor of 30, and the industrial production has multiplied by 50 times. Continuously, we are seeking a balance between our physical being, ability to manage our water resources, and the limitations imposed by the environment. Although progress has improved the quality of life, it has caused significant environmental destruction in such a magnitude that could not be predicted. Now “the environment” is fighting back. The impacts of climate change on natural water resources have been devastating in many regimes around the world. More frequent and intensive floods and droughts have changed the ability of the man-made system to operate and provide services to the public. Also, it has changed the way we have planned and managed our surface and groundwater resources.

A question that should be answered is whether development in the next decades could be done in a way that is economically and ecologically sustainable. We cannot answer this question unless we have a vision of the future and our planning schemes are environmentally responsible and sensitive toward the major elements of our physical environment, namely, air, water, and soil. Water among these elements is of special importance. Excessive use of surface and groundwater, and misusing and polluting these vital resources by residential, agricultural, and industrial wastewater have threatened our well-being. Groundwater is more vulnerable to pollution because it is invisible to monitor and regulatory issues related to groundwater misuse, and laws against contaminating groundwater are not easy to enforce.

Planning for sustainable development of water resources means water conservation, waste and leakage prevention, improved efficiency of water systems, improved water quality, water withdrawal and usage within the limits of the system, water pollution within the carrying capacity of the streams, and water discharge from groundwater within the safe yield of the system. It is not easy to determine and monitor the safe yield of the aquifers. Aquifer safe yields cannot be enforced for many technical, operational, and political resources. So, the aquifers are subject to conditions of over expectation in many parts of the world, especially in arid and semiarid regions, where groundwater is widely used for irrigation.

Water is a sustainable resource and the need for integrated water resources management (IWRM) is in every state and national agenda. Water, as a key element in the formation and conservation of the environment, is receiving global attention more than ever. Water security and water disaster preparedness are the subjects of many global concerns. Figure 1.1 shows a global map of nations’ vulnerability to water scarcity using a composite index based on available water resources and current use, reliability of water supply, and the national incomes (World Resources, 1998).

FIGURE 1.1 Nations’ vulnerability to water scarcity. (From WRI World Resources Institute, World Resources, 1998–1999: A Guide to the Global Environment, Oxford University Press, New York, 384, 1998.)

Approximately 45% of the total irrigated lands in the United States are irrigated by groundwater. In Asia and Africa, more than 60% of land mass is irrigated by groundwater. Libya’s irrigated farming is primarily from low-quality groundwater resources, several kilometers deep.

1.2 WATER AVAILABILITY

Groundwater is one of the main components of the environment that is relatively less affected by short-term climate and hydrologic variability. According to a global model of irrigation requirements, Water Global Assessment and Prognosis (WaterGAP) (Doll, 2002), 36% of the total river runoff is formed by groundwater. Therefore, separating groundwater shares from surface water resources is not easy to assess. The primary input for estimating the volume of water naturally available to a given nation is an information database (AQUASTAT) that has been developed and maintained by the Food and Agriculture Organization of the United Nations (FAO, 2007). It is based on a water balance approach for each country and the quantity of available water resources (FAO, 2003). This database has become a common reference tool used to estimate each nation’s renewable water resources. The FAO has compiled an index called Total Actual Renewable Water Resources (TARWR). This index is a measure of the water resources availability for development from all sources within a region. It is a total-volume figure expressed in km³/year; divided by the total population. The index estimates the total available water resources per person in each country, considering a number of individual resources as follows:

• Adding all internally generated surface and groundwater from precipitation falling within a country’s boundaries

• Adding flow entering from other countries, both surface and groundwater

• Subtracting any potential shared resource from surface and groundwater system interactions

• Subtracting the water that leaves the country through surface and groundwater resources, required by an existing treaty and/or a set by international guidelines.

TARWR gives the maximum amount of water that could actually be available for a country on a per capita basis. From 1989, this method has been used to assess water scarcity and water stress. It is important to note that the FAO considers what is shared in surface and groundwater resources. However, as discussed by the United Nations Educational Scientific and Cultural Organization (UNESCO, 2006), these volumes do not consider the socioeconomic criteria that are applied to societies, nations, or regions that are developing those resources. Water pricing and net costs can vary when developing surface and groundwater sources. Therefore, the reported renewable volume of water will be less available for a variety of economic and technical reasons. Simply, a lot of water is not used because of the circumstances that control the supply and the demand. The following factors should be considered when using the TARWR index (UNESCO, 2006):

• Roughly 27% of the surface water runoff is floods, and this share of water is not considered as a usable resource. Despite that, floods are counted in the nations’ TARWR as part of the available, renewable annual water resource.

• Seasonal variation in precipitation, runoff, and recharge, is not well reflected in annual figures. However, it is important in the assessment of supply and demand spatial and temporal distribution for basin-scale decision-making and strategy setting.

• Many sizable countries have different climatic zones as well as scattered population, and the TARWR does not reflect the ranges of these factors that can vary in different regions in that country.

• TARWR has no data to identify the volume of water that sustains ecosystems, namely, the volume that provides water for forests, direct rain fed agriculture, grazing, grass areas, and environmental demand.

It is also documented that not all of the renewable freshwater resources can be used and controlled by the population of a country. It is estimated that only about one-third of the renewable freshwater resources can potentially be controlled even with the most technical, structural, nonstructural, social, environmental, and economic means. The global potentially useable water resources of the renewable freshwater resources are estimated to be around 9000–14,000 km³ (Secker, 1993; UN, 1999). A part of the primary water supply (PWS) is evaporated, other parts return to rivers, streams, and aquifers and in many instances withdrawn again for different uses. This is known as the recycled portion of the PWS. The PWS and the recycled water supply adds up to 3300 km³ that constitute the water used in different sectors such as agriculture, industry, public, and water supply.

1.2.1 GROUNDWATER AVAILABILITY

Groundwater is by far the most abundant source of freshwater on continents outside polar regions, followed by ice caps, lakes, wetlands, reservoirs, and rivers. In 2012, UNESCO reported that about 2.5 billion people depended solely on groundwater for their drinking water supply (WRI, 1998). It is estimated that about 20% of global water withdrawals come from groundwater (WMO, 1997).

According to the United Nations Environment Programme, annual global freshwater withdrawal has grown from 3790 km³ in 1995 to about 4430 km³ in 2000. The annual global water withdrawal is expected to increase with a rate of 10%–20% every 10 years, reaching approximately 5240 km³ in 2025. The share of groundwater is expected to increase at a slower rate due to already over drafted aquifers in many points of the world.

There are many advantages in storage of groundwater compared to the surface storage:

1. Minimum evaporation losses—it is limited to

a. Groundwater close to the surface by capillary fringes.

b. “Phreatophytes”—plants feed on capillary fringe.

2. Quality may benefit from filtering action (however, may be too high in dissolved solids). There is general improvement of water quality because of the porous media filtration of airborne and surface runoff contaminants and pathogens.

3. Outflow is gradual (good regulation in underground reservoir).

4. No other massive structure such as dams is needed (however, may involve high pumping costs).

5. Land use above the groundwater resources can be continued without change (there is no submergence of houses, abstraction to infrastructure, and property development and agricultural development).

Groundwater quality is under continuous threats. Unless protected, groundwater quality deteriorates from saline intrusion, pollution from agricultural and urban activities, uncontrolled wastewater, as well as solid and hazardous waste disposal. The following activities should be undertaken:

• Improve the understanding of groundwater contribution to the hydrologic cycle and evaluate changes to groundwater storage and water table fluctuations.

• Raise the awareness of decision-makers, water users, and public on the importance of groundwater in order to encourage protection and sustainable use.

• Assess the impacts of economic development on groundwater resources and support international collaboration for nations and regional needs.

• Quantify climate change impacts on groundwater resources including sea levels rise and intrusion of saltwater.

1.3 GROUNDWATER SYSTEMS

The groundwater system is a part of the hydrologic cycle and should be studied on a watershed scale. Combination of many elements and factors affect groundwater, requiring a holistic view to groundwater challenges within a hydrologic cycle.

Groundwater systems are traditionally developed as sources of water for different uses of domestic, industrial, or agricultural purposes. The generally good quality of the water and its accessibility in many regions of the world, where surface water is nonexistent or extremely costly to develop, have been important factors in stimulating the development of this relatively low-cost, ...