Inflow (hydrology)

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Torrente Pescone, one of the inflows of Lake Orta (Italy). Pescone alla foce.jpg
Torrente Pescone, one of the inflows of Lake Orta (Italy).
Visual description of Hydrologic Cycle Watercyclesummary.jpg
Visual description of Hydrologic Cycle

In hydrology, the inflow is the water entering a body of water. It can also refer to the measure of average volume of incoming water per unit time. It is contrasted with outflow.



Inflow [1] is a process within the hydrologic cycle that helps maintain the water levels within all bodies of water.

All bodies of water have multiple inflows, but often, one inflow may predominate and be the largest source of water. However, in many cases, no single inflow will predominate and there will be multiple primary inflows. For a lake, the inflow may be a river or stream that flows into the lake. Inflow may also be, strictly speaking, not flows, but rather precipitation, like rain.

Inflow can also be used to refer to groundwater recharge.

Hydrologic Cycle

The hydrologic cycle, [2] or water cycle, has no true starting point. However, it’s easiest to start with the ocean, as the ocean makes up the majority of Earth’s water. The sun is the main aspect of the hydrologic cycle, as it is responsible for warming the water and causing evaporation. As water evaporates into the air and the rising air currents take the evaporated water into the atmosphere. Once the evaporated water reaches high enough in the atmosphere, it reaches cooler temperatures, which cause the vapor to condense into clouds.

Air currents are capable of moving clouds around the globe, but typically cloud particles collide and fall out of the sky as precipitation. Even though precipitation can fall in many forms and in many locations, most precipitations either ends up back into a body of water or on land as surface runoff. [3] A portion of runoff enters back into streams and rivers, which over time lead back to the ocean. Another portion of runoff soaks into the ground as groundwater seepage, and are stored in freshwater lakes. [4] The other portion of runoff soaks into the ground as infiltration, some of this water will infiltrate deep into the ground and replenish aquifers. [2]

Inflow and the Hydrologic Cycle

So how does inflow play a role in the hydrologic cycle? Inflow is the adding of water to the different aspects of the hydrologic system. Consequently, outflow is the removal of water from the hydrological cycle. Inflow adds water to different aspects of the hydrologic cycle that returns water storage to an even level. Water storage is the retention of water throughout different aspects of the hydrologic cycle. Due to the fact that water movement is cyclical, [5] inflow, outflow, and storage are all aspects of the hydrologic cycle.

Inflow = Outflow +/- Changes in Storage [5]

Related Research Articles

Hydrology The science of the movement, distribution, and quality of water on Earth and other planets

Hydrology is the scientific study of the movement, distribution, and management of water on Earth and other planets, including the water cycle, water resources, and environmental watershed sustainability. A practitioner of hydrology is called a hydrologist. Hydrologists are scientists studying earth or environmental science, civil or environmental engineering, and physical geography. Using various analytical methods and scientific techniques, they collect and analyze data to help solve water related problems such as environmental preservation, natural disasters, and water management.

Water cycle Continuous movement of water on, above and below the surface of the Earth

The water cycle, also known as the hydrologic cycle or the hydrological cycle, describes the continuous movement of water on, above and below the surface of the Earth. The mass of water on Earth remains fairly constant over time but the partitioning of the water into the major reservoirs of ice, fresh water, saline water and atmospheric water is variable depending on a wide range of climatic variables. The water moves from one reservoir to another, such as from river to ocean, or from the ocean to the atmosphere, by the physical processes of evaporation, condensation, precipitation, infiltration, surface runoff, and subsurface flow. In doing so, the water goes through different forms: liquid, solid (ice) and vapor.

Endorheic basin Closed drainage basin that allows no outflow

An endorheic basin is a drainage basin that normally retains water and allows no outflow to other external bodies of water, such as rivers or oceans, but drainage converges instead into lakes or swamps, permanent or seasonal, that equilibrate through evaporation. They are also called closed or terminal basins or internal drainage systems or basins. Endorheic regions contrast with exorheic regions. Endorheic water bodies include some of the largest lakes in the world, such as the Caspian Sea, the world's largest inland body of water.

Fossil water or paleowater is an ancient body of water that has been contained in some undisturbed space, typically groundwater in an aquifer, for millennia. Other types of fossil water can include subglacial lakes, such as Antarctica's Lake Vostok, and even ancient water on other planets.

Ecohydrology is an interdisciplinary scientific field studying the interactions between water and ecological systems. It is considered a sub discipline of hydrology, with an ecological focus. These interactions may take place within water bodies, such as rivers and lakes, or on land, in forests, deserts, and other terrestrial ecosystems. Areas of research in ecohydrology include transpiration and plant water use, adaption of organisms to their water environment, influence of vegetation and benthic plants on stream flow and function, and feedbacks between ecological processes and the hydrological cycle.

The United States Environmental Protection Agency (EPA) Storm Water Management Model is a dynamic rainfall–runoff–subsurface runoff simulation model used for single-event to long-term (continuous) simulation of the surface/subsurface hydrology quantity and quality from primarily urban/suburban areas. It can simulate the Rainfall- runoff, runoff, evaporation, infiltration and groundwater connection for roots, streets, grassed areas, rain gardens and ditches and pipes, for example. The hydrology component of SWMM operates on a collection of subcatchment areas divided into impervious and pervious areas with and without depression storage to predict runoff and pollutant loads from precipitation, evaporation and infiltration losses from each of the subcatchment. Besides, low impact development (LID) and best management practice areas on the subcatchment can be modeled to reduce the impervious and pervious runoff. The routing or hydraulics section of SWMM transports this water and possible associated water quality constituents through a system of closed pipes, open channels, storage/treatment devices, ponds, storages, pumps, orifices, weirs, outlets, outfalls and other regulators. SWMM tracks the quantity and quality of the flow generated within each subcatchment, and the flow rate, flow depth, and quality of water in each pipe and channel during a simulation period composed of multiple fixed or variable time steps. The water quality constituents such as water quality constituents can be simulated from buildup on the subcatchments through washoff to a hydraulic network with optional first order decay and linked pollutant removal, best management practice and low-impact development removal and treatment can be simulated at selected storage nodes. SWMM is one of the hydrology transport models which the EPA and other agencies have applied widely throughout North America and through consultants and universities throughout the world. The latest update notes and new features can be found on the EPA website in the download section. Recently added in November 2015 were the EPA SWMM 5.1 Hydrology Manual and in 2016 the EPA SWMM 5.1 Hydraulic Manual and EPA SWMM 5.1 Water Quality Volume (III) + Errata

Surface runoff Flow of excess rainwater not infiltrating in the ground over its surface

Surface runoff is the flow of water occurring on the ground surface when excess rainwater, stormwater, meltwater, or other sources, can no longer sufficiently rapidly infiltrate in the soil. This can occur when the soil is saturated by water to its full capacity, and that the rain arrives more quickly than the soil can absorb it. Surface runoff often occurs because impervious areas do not allow water to soak into the ground.Furthermore, runoff can occur either through the natural or man-made processes.Surface runoff is a major component of the water cycle. It is the primary agent of soil erosion by water. The land area producing runoff that drains to a common point is called a drainage basin.

Water balance Looks at how water moves in a closed system

The law of water balance states that the inflows to any water system or area is equal to its outflows plus change in storage during a time interval. In hydrology, a water balance equation can be used to describe the flow of water in and out of a system. A system can be one of several hydrological or water domains, such as a column of soil, a drainage basin, an irrigation area or a city. Water balance can also refer to the ways in which an organism maintains water in dry or hot conditions. It is often discussed in reference to plants or arthropods, which have a variety of water retention mechanisms, including a lipid waxy coating that has limited permeability.

Streamflow, or channel runoff, is the flow of water in streams, rivers, and other channels, and is a major element of the water cycle. It is one component of the runoff of water from the land to waterbodies, the other component being surface runoff. Water flowing in channels comes from surface runoff from adjacent hillslopes, from groundwater flow out of the ground, and from water discharged from pipes. The discharge of water flowing in a channel is measured using stream gauges or can be estimated by the Manning equation. The record of flow over time is called a hydrograph. Flooding occurs when the volume of water exceeds the capacity of the channel.

Open and closed lakes refer to the major subdivisions of lakes – bodies of water surrounded by land. Exorheic, or open lakes drain into a river, or other body of water that ultimately drains into the ocean. Endorheic basins fall into the category of endorheic or closed lakes, wherein waters do not drain into the ocean, but are reduced by evaporation, and/or drain into the ground.

Subsurface flow, in hydrology, is the flow of water beneath earth's surface as part of the water cycle.

Perennial stream type of river

A perennial stream or perennial river is a stream or river (channel) which has constant stream throughout the year through parts of its stream bed during years of normal rainfall. In the absence of irregular, prolonged, or extreme drought, a perennial stream is a watercourse, or segment, element, or emerging body of water which continually delivers groundwater. For example, an artificial disruption of stream, variability in flow or stream selection associated with the activity in hydropower installations, shall not affect the measurement. Perennial streams do not consist of stagnant water for the wetlands, reservoirs, and ponds that occur all the period. All other streams, or portions thereof, should be considered seasonal rivers or lakes. The stream can cycle from broken to perpetual through multiple iterations, to intermittent through its mechanism.

Surface water

Surface water is water located on top of the Earth's surface such as rivers, creeks, and wetlands. This may also be referred to as blue water. The vast majority is produced by precipitation and water runoff from nearby areas. As the climate warms in the spring, snowmelt runs off towards nearby streams and rivers contributing towards a large portion of our drinking water. Levels of surface water lessen as a result of evaporation as well as water moving into the ground becoming ground-water. Alongside being used for drinking water, surface water is also used for irrigation, wastewater treatment, livestock, industrial uses, hydropower, and recreation. It is recorded by the Environmental Protection Agency (EPA), that approximately 68 percent of water provided to communities comes from surface water. For USGS water-use reports, surface water is considered freshwater when it contains less than 1,000 milligrams per liter (mg/L) of dissolved solids.

Water resources Sources of water that are potentially useful

Water resources are natural resources of water that are potentially useful. 97% of the water on the Earth is salt water and only three percent is fresh water; slightly over two thirds of this is frozen in glaciers and polar ice caps. The remaining unfrozen freshwater is found mainly as groundwater, with only a small fraction present above ground or in the air. Natural sources of fresh water include surface water, under river flow, groundwater and frozen water.

Stream Body of surface water flowing down a channel

A stream is a body of water with surface water flowing within the bed and banks of a channel. The flow of a stream is controlled by three inputs – surface water, subsurface water and groundwater. The surface and subsurface water are highly variable between periods of rainfall. Groundwater, on the other hand, has a relatively constant input and is controlled more by long-term patterns of precipitation. The stream encompasses surface, subsurface and groundwater fluxes that respond to geological, geomorphological, hydrological and biotic controls.

Hydrology (agriculture)

Agricultural hydrology is the study of water balance components intervening in agricultural water management, especially in irrigation and drainage.

The following outline is provided as an overview of and topical guide to hydrology:

Droughts in California Overview of the occurrence, presence and intensity of droughts in the U.S. state of California

Throughout history, California has experienced many droughts, such as 1841, 1864, 1924, 1928–1935, 1947–1950, 1959–1960, 1976–1977, 1986–1992, 2006–2010, 2011–2017, 2018 and 2020 which continues to this day. As the most populous state in the United States and a major agricultural producer, drought in California can have a severe economic as well as environmental impact. Drought may be due solely to, or found in combination with, weather conditions; economic or political actions; or population and farming.

Fresh water naturally occurring water with low amounts of dissolved salts

Fresh water is any naturally occurring water except seawater and brackish water. Fresh water is generally characterized by having low concentrations of dissolved salts and other total dissolved solids. Though the term specifically excludes seawater and brackish water, it does include mineral-rich waters such as chalybeate springs. Fresh water may include water in ice sheets, ice caps, glaciers, icebergs, bogs, ponds, lakes, rivers, streams, and even underground water called groundwater.


  1. "The Hydrologic Cycle | Freshwater Inflows". Retrieved 2020-12-09.
  2. 1 2 "Precipitation and the Water Cycle". Retrieved 2020-12-09.
  3. DOC, NOAA. "Description of the Hydrologic Cycle". Retrieved 2020-12-09.
  4. "Groundwater Flows Underground". Retrieved 2020-12-09.
  5. 1 2 "Water Research Center - Watershed and Water Resource Budgets". Retrieved 2020-12-09.

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