Insight Fundamentals of Hydrology

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he availability of water is crucial to all living species and to maintaining the ecosystems of our precious blue planet. As said before, the existence or lack of water at sufficient quantity and quality could significantly have an effect on the sustainability of life. With that statement, it is very important for the engineers and environmental personnel to have a concrete understanding of our water source and its allocation in nature. Our world contains about 70 percent of water and our own body also with the same percentage, thus very important for survival!

Hydrology is a multi-disciplinary subject that deals with the question of how much water can be expected at any particular time and location. A practitioner of hydrology is a hydrologist, working within the fields either the Earth or environmental science, physical geography or civil and environmental engineering. The application of this subject is important to ensuring adequate water for such purposes as drinking, irrigation, agricultural and industrial uses, as well as flooding prevention.

The surface water hydrology focuses on the distribution of water on or above the Earth’s surface. It encompasses all water in the rivers, lakes, and streams, on land and in the air. Whereas ground water hydrology deals with the distribution of water in the Earth’s sub-surface geological materials, such as rock, gravel, and sand.

Hydrological Cycle

The hydrological cycle is defined as the movement and the conservation of water on our world. This cycle includes all the water on and in the Earth, including salt, fresh water, surface water, groundwater, water from beneath the ground surface, and so forth.

Water is transferred to the Earth’s atmosphere through two distinct processes: evaporation and transpiration. However, the third process is derived from the two terms and is named as evapotranspiration. Evaporation converts liquid water from rivers, lakes, streams, and other bodies of water to water vapour (gases form). Transpiration is the process by which water is emitted from plants through the stomata, small openings on the underside of leaves connected to the vascular tissue. It occurs predominantly at the leaves while the stomata are open for the passage of carbon dioxide and oxygen during photosynthesis. Because it is often difficult to differentiate between the true evaporation and transpiration, so that is how the hydrologist used the term evapotranspiration to best describe the combination of water losses due to evaporation and transpiration process.

Precipitation is the primary mechanism by which water is released from the atmosphere. It takes several forms and the most common of which in temperate climates is rain. Additionally, water can fall as snow, hail, sleet, and freezing rain. The ocean evaporation is the greatest source (approximately 90 percent) of precipitation. As the water fall to Earth’s surface, the droplets either run over the ground into streams and rivers (referred as surface runoff, overland flow, or direct runoff), move laterally just below the ground surface (interflow), or move vertically through the soils to form groundwater (terms as infiltration or percolation). The movement of water through several of the hydrological cycle is extremely complex because it is erratic in both time and location.

Among the most important terms for a water budget are:

• Evaporation (E)
• Transpiration (E_T)
• Precipitation (P)
• Infiltration (G)
• Interflow (F)
• Surface runoff (R)

Surface runoff is the water that flows across the land surface after a storm event that later will eventually developed rivers and streams due to long term effects. As rain falls over land, part of that gets infiltrated the surface as overland flow. Some portion of the precipitation that falls down on ground surface do not flows out as runoff will get stored as surface water bodies like lakes, reservoirs and swamps or as sub-surface water body, normally called groundwater. Groundwater storage is the water infiltrating through the soil cover of a land surface and traveling further to reach the huge body of water underground.

Applications of Hydrology

• Determination of the water balance of a region and agricultural water balance.
• Designing riparian restoration projects, irrigation schemes and operating agricultural productivity.
• Providing adequate supply for drinking water and other purposes at residential, commercial, and industrial zone.
• Design and construction of bridges, ports, dams (for water supply or hydroelectric power-plant), and drainage systems.
• Real-time flood forecasting and warning, plus part of the hazard module in catastrophe modeling.
• Mitigating and predicting flood, landslide, drought risk, and prediction of geomorphological changes, such as erosion or sedimentation.
• Studying by research the impacts of precursor moisture on sanitary sewer systems.

In conclusion, water is very important for our survival and keeping balance in temperature. In conjunction with understanding water resources, hydrology is one subject that we surely don’t want to miss (exciting and related to environmental engineering) as it provides the knowledge acquired in civil engineering.