Define Runoff.

Runoff refers to the movement of water over the land surface or through the soil, ultimately flowing into streams, rivers, lakes, or oceans. It occurs when precipitation, such as rain, snow, or sleet, exceeds the infiltration capacity of the soil, leading to excess water that cannot be absorbed and retained within the soil profile. Instead, this surplus water accumulates on the surface and begins to flow downhill under the influence of gravity, forming surface runoff.

Surface runoff can originate from various sources, including rainfall, snowmelt, irrigation, and stormwater runoff from impervious surfaces such as roads, parking lots, and rooftops. It plays a critical role in the hydrological cycle, transporting water, sediment, nutrients, pollutants, and organic matter across landscapes, influencing soil erosion, water quality, and ecosystem dynamics.

Factors influencing runoff generation include rainfall intensity, duration, frequency, soil characteristics, land use, topography, and vegetation cover. Intense or prolonged rainfall events, compacted soils, steep slopes, and land development can increase runoff rates by reducing infiltration capacity, promoting surface runoff, and accelerating water flow over the land surface.

Runoff is a key component of the water cycle, contributing to streamflow, groundwater recharge, and freshwater availability, while also shaping the physical and chemical properties of rivers, lakes, and coastal environments. Managing runoff is essential for sustainable water resources management, flood control, erosion prevention, and protecting aquatic ecosystems and water quality. Implementing practices such as green infrastructure, soil conservation, stormwater management, and land use planning can help reduce runoff rates, mitigate flood risks, and promote the sustainable use of water resources.