Role of Rivers

A river basin is a natural unit for water and land management. Planning should consider the whole basin together.

During a flood, river water spreads beyond its banks and loses velocity. Relatively heavier sand and silt are deposited first near the banks, while finer particles are carried farther onto the floodplain. Repeated floods build raised natural levees along the channel. Sea-wave erosion is a coastal process, and wind deposition forms dunes in dry regions. Exam tip: remember that natural levees are depositional landforms found beside a river on its floodplain.

Rivers are a base for many organisms and wetland systems. Do not see a river only as a water source.

Sand helps keep the river bed and banks balanced. Excess mining increases erosion and instability.

Polluted water entering a river can contain harmful substances, disease-causing organisms, excess nutrients, or other unwanted materials. Such water may no longer be safe for direct drinking. Before it is supplied for human consumption, it generally needs suitable treatment, such as removing suspended matter, reducing harmful organisms, and checking its quality. The exact treatment depends on the type and amount of pollution. Pollution can therefore increase the cost, effort, and importance of water purification, even though treatment may make some water usable again.

Option A is correct because contamination increases the need for treatment before river water can be used as drinking water. The other choices do not follow from pollution. Polluted water does not automatically become safer, a river does not immediately dry up, and silt does not completely disappear. The answer also does not claim that treatment always removes every contaminant; it states the practical consequence that more purification is required. Safe drinking-water use depends on testing, proper treatment, and protection of the source.

An estuary forms where a river meets the sea and freshwater mixes with saltwater in a tidal, funnel-shaped mouth. Strong tides, waves, or coastal currents can carry suspended sediment away instead of allowing it to build outward. When deposition is not strong enough to create distributaries and a growing sediment body, an estuary is more likely than a delta.

Option B is correct because tides and waves removing deposits prevent large amounts of silt from settling at the river mouth. High silt supply and a calm sea would favour delta formation, so option A describes the opposite situation. A river must have a mouth to meet the sea, and ending in a lake does not describe a marine estuary.

As a river flows downstream, larger fragments are repeatedly broken by abrasion and are deposited relatively earlier when the river lacks enough energy to carry them. Finer materials such as sand, silt and clay remain in transport for longer distances. Therefore, sediment generally becomes finer downstream. Option A is not the main reason; a loss of water alone does not explain sorting by particle size. Exam tip: remember—coarser sediment in the upper course and finer sediment in the lower course.

Many communities and uses depend on river water. Equitable use needs both balance and responsibility.

Soil eroded from the catchment increases silt in the river. Therefore soil conservation is linked to river health.

Wetlands beside rivers act like natural sponges: they temporarily store excess rainwater or floodwater. This can reduce the peak flow and pressure of water in the river, making them important for flood management. They do not dry up rivers or stop all deposition. Exam tip: Remember wetlands for water storage, groundwater recharge, and reducing flood impacts.

A flood line marks, or helps estimate, the area that may be reached by floodwater under a particular flood level or probability. Planned settlements consider it so that houses, roads, public services, and other valuable structures are not placed in areas likely to be inundated. Therefore, option C is correct. Using flood-line information can reduce danger to people and limit damage to property, although it cannot remove all flood risk.

The other choices are unrelated. A flood line does not measure sea depth, determine the age of mountains, or turn a river into minerals. Its purpose is connected with water spread during floods. A planner can compare the line with proposed building locations and maintain safer setbacks or restrict construction in high-risk zones. Thus the phrase “possible water spread area” gives the direct reason for considering a flood line, making C the correct answer.

A river’s course is linked to natural slope and flow. Unplanned changes can increase disaster risk.

A river keeps depositing silt at its mouth and can create new land. This is the basis of delta formation.

River valleys provide both resources and connectivity. This can increase trade activities.

In the lower course the river slows down and deposits more material. Link deposition with lower energy.

Cities have higher domestic and industrial needs. Therefore urban pressure is important in river management.

Bank erosion can affect fields, roads and houses. It is necessary to understand erosion risk near river settlements.

Water storage and crop planning must match seasonal flow. This is more important in monsoon-fed rivers.

Reduced flow affects aquatic organisms and wetlands. Maintaining environmental flow is necessary.

A floodplain is a relatively flat area beside a river that may receive rich deposits of soil when the river overflows. These deposits can make the land productive for farming, but the same location can be exposed to future floods. When water levels rise, the river may spread across the plain, damaging homes, crops, roads and other property. Therefore, option C is correct. Fertility offers an advantage, but it does not remove the physical risk of flooding.

The reasoning requires considering both benefits and hazards. River flooding can leave nutrient-rich sediment, which explains why people may value floodplain land. However, a floodplain is formed or affected by the river’s overflow, so it remains a natural area of possible water spread. The choices saying water never reaches the area or that fertile land is always safe are clearly incorrect. Soil does not normally become rock simply because the land is a floodplain. Thus, option C gives the accurate reason for settlement risk.