1.1. What is hydrology?

Hydrology is the study of the origin, occurrence, and behavior of water in all its forms on and beneath the Earth’s surface. Additionally, hydrology forms the foundation for water management, which makes the hydrological cycle useful for society, both in terms of quantity and quality. Over the past few decades, hydrology has undergone significant development. In addition to the quantitative approach, the qualitative perspective has also become increasingly important. At a certain point, the field of hydrology became so broad that specialists divided it into subfields. This led to areas such as surface water hydrology, geohydrology, ecohydrology, environmental hydrology, agrohydrology, and more. However, this division is not ideal. Hydrology is the science that studies the entire water cycle, with the interconnectedness of these subfields being essential. Groundwater and surface water cannot be separated, and ecology, agriculture, water quality, and the environment are inherently linked to both groundwater and surface water.

Hydrology in Civil Engineering

Hydrology plays a pivotal role in civil engineering, offering essential insights and data for various aspects of infrastructure development and management. It is integral to hydraulic engineering, enabling the design of flood control systems and stormwater management solutions for community safety. Hydrology’s contributions extend to optimizing water supply and distribution systems, wastewater treatment, and irrigation systems for efficient water resource utilization. Additionally, it facilitates collaboration between hydrologists and civil engineers in sustainable urban planning and environmental conservation efforts, addressing issues like urban runoff and pollution control to create healthier environments.

In practice, the hydrologist’s task is to determine the inputs and outputs of a hydrological system, such as a river, lake, or water-bearing layer in the ground (aquifer). They also describe the movement of water through the system. The work of a hydrologist can be categorized into three areas of focus: water usage, water management, and water pollution.

1.1.1. Water usage

Water usage involves extracting water from a river, lake, or aquifer to supply water to cities, industries, and agriculture. Major water users include facilities like power plants that require significant amounts of cooling water. Water is also used for energy generation (hydropower), recreation, and protecting the flora and fauna in an area. The hydrologist can determine the water supply to a system under various conditions, such as during a period of drought.

1.1.2. Water management

Water management involves all measures aimed at coping with hydrological extremes. Traditionally, this primarily concerns high river discharges (floods) along with accompanying sediment transport. In recent years, there has been renewed focus on low river discharges (droughts) and their consequences. These measures often manifest as civil engineering projects such as dams and dikes, as well as policies and planning for the development of flood-prone areas.

1.1.3. Water pollution

Water pollution involves preventing the spread of contamination and pollutants in natural waters and the removal of existing pollutants. The hydrologist must be able to identify the source and extent of the pollution. Additionally, it is important to understand how quickly and how far the pollution will spread and where it will ultimately end up.

The hydrologist plays a crucial role in addressing various water-related issues. Hydrology aims to quantify the effect of various changes in a watershed. In hydrology, measurements are taken from the natural system, discharge values are determined, and time series of precipitation data are analyzed. In short, efforts are made to quantitatively describe the water system based on physical laws or statistical relationships. Having access to measurement data over a sufficiently long period is essential. However, measuring is expensive, and budget constraints have led to reductions in measurement activities, especially when rare events like waterlogging or floods occur. Moreover, measuring is often not considered the most attractive scientific work. Fortunately, there is currently a noticeable trend where the observation, collection, and preservation of measured data are being increasingly valued. This is evident in the willingness to collaborate in monitoring efforts on both national and international levels.