TOEFL Complete the Words: Hydrology (Intermediate)
Hydrology in TOEFL
Hydrology is the study of how water behaves once it enters the environment. Rather than treating rain, rivers, or floods as separate topics, the field tries to explain the connection between them. It asks what happens after water reaches the ground, why some of it moves quickly toward a channel, and why some of it remains in place for a time before appearing elsewhere. The central concern is not a single event but the sequence through which water is stored, delayed, and eventually released.
In TOEFL passages, hydrology often appears through a process-based explanation. A passage may begin with rainfall or rising river levels, then shift toward the hidden movement that links one stage to the next. Because of that, the key to reading well is to follow the chain of cause and effect carefully. The main point is often not the visible outcome itself, but the mechanism that produced it.
Practice Questions
Question 1
Heavy rain can produce a flood long after the storm itself has weakened. In hydrology, that timing matters because water m_ _ _ _ through a basin step b_ step before it reaches the main cha_ _ _ _. A portion runs o_ _ _ the surface, while another portion enters the soil and stays there temporarily. The ri_ _ of a river may therefore reflect movement that began much earlier. Hydrologists study this l_ _ closely, since flood risk de_ _ _ _ _ not only on rainfall but on the speed with which stored water is released into the channel. A basin that ret_ _ _ _ water can slow the river’s response. A basin that drains quickly can make peak flow much more severe.
Explanation
Complete passage
Heavy rain can produce a flood long after the storm itself has weakened. In hydrology, that timing matters because water moves through a basin step by step before it reaches the main channel. A portion runs over the surface, while another portion enters the soil and stays there temporarily. The rise of a river may therefore reflect movement that began much earlier. Hydrologists study this lag closely, since flood risk depends not only on rainfall but on the speed with which stored water is released into the channel. A basin that retains water can slow the river’s response. A basin that drains quickly can make peak flow much more severe.
Hydrology examines how water moves after it reaches the ground. The subject is concerned not just with rainfall itself, but with the delay between rainfall and the response of a river. Water follows more than one path through a landscape, so the visible rise of a channel may come from processes that started some time before.
That delay is important because it affects flood intensity. When water remains in soil or other forms of storage, the river responds more slowly. When stored water reaches the channel quickly, flow can increase sharply. In passages like this, the key idea is usually the timing of movement. The visible result matters, but the real explanation lies in the process that produced it.
Question 2
Groundwater moves so slowly that its importance can be easy to overlook. In hydrology, however, water st_ _ _ _ below the sur_ _ _ _ plays a major role _ _ shaping river behavior during dry per_ _ _ _. A stream fed by groundwater may con_ _ _ _ _ flowing even after rain has become sca_ _ _, because water from under the ground enters the channel gradually. This steady input is called baseflow. Hydrologists study it closely because it he_ _ _ explain why some rivers shrink quickly while others remain relatively stable. The answer often l_ _ _ in the material beneath the surface. Permeable rock can store water and release it over time, whereas dense layers restrict mov_ _ _ _ _ and reduce that long-term support.
Explanation
Complete passage
Groundwater moves so slowly that its importance can be easy to overlook. In hydrology, however, water stored below the surface plays a major role in shaping river behavior during dry periods. A stream fed by groundwater may continue flowing even after rain has become scarce, because water from under the ground enters the channel gradually. This steady input is called baseflow. Hydrologists study it closely because it helps explain why some rivers shrink quickly while others remain relatively stable. The answer often lies in the material beneath the surface. Permeable rock can store water and release it over time, whereas dense layers restrict movement and reduce that long-term support.
This passage deals with groundwater and its influence on rivers. Hydrology is concerned with visible water such as streams and lakes, yet a great deal of attention is also given to water hidden below the surface. During a dry spell, that underground supply can become especially important because it enters a river slowly and helps sustain flow after recent rain is gone.
The key term here is baseflow. It refers to the portion of streamflow supported by groundwater rather than by immediate surface runoff. Rivers with strong groundwater input often change more gradually, while rivers with limited underground support can weaken much faster. That is why hydrologists care about soil and rock conditions beneath a basin. Those hidden features influence how long water is stored and how steadily it reaches the channel.
Question 3
Warm weather can lower the amount of water that remains available in a drainage basin even when rainfall has been adequate. One reason is evapotranspiration, the pr_ _ _ _ _ through which water returns to the atm_ _ _ _ _ _ _ from land and vegetation. When temp_ _ _ _ _ _ _ _ rise, soil moisture may disappear faster, and plants may dr_ _ more water upward before releasing it through their leaves. As a result, less water remains near the surface to support later streamflow. Hydrologists study this process carefully because it can inf_ _ _ _ _ how quickly a basin becomes dry after a rainy period. A region with high atmospheric dem_ _ _ may lose water rapidly, which leaves rivers more valn_ _ _ _ _ _ to seasonal decline.
Explanation
Complete passage
Warm weather can lower the amount of water that remains available in a drainage basin even when rainfall has been adequate. One reason is evapotranspiration, the process through which water returns to the atmosphere from land and vegetation. When temperatures rise, soil moisture may disappear faster, and plants may draw more water upward before releasing it through their leaves. As a result, less water remains near the surface to support later streamflow. Hydrologists study this process carefully because it can influence how quickly a basin becomes dry after a rainy period. A region with high atmospheric demand may lose water rapidly, which leaves rivers more vulnerable to seasonal decline.
This passage focuses on a process that removes water from the land rather than adding it. In hydrology, that process matters because the amount of rainfall alone does not determine how much water will remain in a basin. Part of that water returns to the atmosphere after reaching the ground, and the loss can become especially important in warm conditions.
The key term here is evapotranspiration. It combines evaporation from soil or other surfaces with transpiration from plants. Once that process becomes stronger, soil moisture can fall more quickly, and less water may remain available to support rivers later. That is why hydrologists pay attention to temperature and vegetation as well as rainfall. A basin may receive enough rain for a time, yet still become water-stressed if losses to the atmosphere continue at a high rate.
