A watershed, also called a "drainage basin" in North America, is an area in which all water flowing into it goes to a common outlet or body of watersuch as the same estuary or reservoir. Watersheds themselves consist of all surface water and include lakes, streams, reservoirs, and wetlands, as well as all groundwater and aquifers. The water in a watershed originates via precipitation that is collected on the surface and groundwater.
However, it is important to note that not all precipitation falling in an area exits the watershed.
Some of it is lost through evaporation and transpiration and some is used by people and some soaks into the soil and groundwater. At the boundaries of watersheds, there are drainage divides usually in the form of ridges or hills.
Here the water flows into two separate watersheds and does not always end up in a common outlet. In the United States, for example, there are many different watersheds, but the largest is the Mississippi River basin which drains water from the Midwest into the Gulf of Mexico.
This water does not enter the Pacific Ocean because the Rocky Mountains act as the drainage divide.
The Mississippi River basin is an example of an extremely large watershed, but watersheds vary in size. Some of the world's largest ones contain smaller watersheds within them depending on where the final water outlet is.
The second is called a major drainage divide. In this situation, waters on each side of the boundaries do not meet via the same river or stream, but they do reach the same ocean.
For example, there is a drainage divide between the Yellow River Huang He basin and the Yangtze River in China but both have the same outlet. The final type of drainage divide is called a minor drainage divide. In these, waters separate at the divide but later rejoin. An example of this situation is shown with the Mississippi and Missouri Rivers. The second feature is the drainage divide or watershed boundary, such as a mountain range. This plays a role because it helps in determining whether the water in the watershed is flowing toward or away from an area.
The next feature is the topography or terrain of the watershed's land. If the area is steep, the water there is likely to flow quickly and cause flooding and erosion, whereas flat watersheds have often had slower flowing rivers.
The final feature of a watershed's physical landscape is its soil type.
Overview of Watersheds and Watershed Management
Sandy soils, for example, absorb water quickly, while hard, clay soils are less permeable. Both of these have implications for runoff, erosion, and groundwater. By studying the key watershed features in addition to activities along waterways scientists, other researchers and city governments can work to keep them healthy because a small change in one portion of a watershed can drastically affect other parts.
Watershed pollution occurs in two ways: point source and nonpoint source.
Point source pollution is pollution that can be traced to a specific point such as a disposal site or leaking pipe. Recently, laws and technological advances have made it possible to detect point source pollution and its problems are being reduced.
Nonpoint source pollution occurs when pollutants are found in water running off of crops, parking lots and other lands. In addition, it can also be caused when particulates in the atmosphere fall onto the land with precipitation.
Humans have also impacted watersheds by reducing the amount of water flowing within them. As people take water out of a river for irrigation and other city-wide uses, the river's flow decreases and with this decreased flow, natural river cycles such as flooding, may not occur.Science Explorer. Frequently Asked Questions. Multimedia Gallery. Park Passes.
Employees in the News. Emergency Management. Some or all of this iron can precipitate to form the red, orange, or yellow sediments in the bottom of streams containing mine drainage. The acid runoff further dissolves heavy metals such as copper, lead, and mercury into groundwater or surface water.
The rate and degree by which acid-mine drainage proceeds can be increased by the action of certain bacteria. Acid mine drainage AMD consists of metal-laden solutions produced by the oxidative dissolution of iron sulfide minerals exposed to air, moisture, and acidophilic microbes during the mining of coal and metal deposits.
The pH of AMD is usually in the range of 2—6, but mine-impacted waters at circumneutral pH 5—8 are also common. Mine drainage Historical mining has left complex problems in catchments throughout the world. Land managers are faced with making cost-effective plans to remediate mine influences. Remediation plans are facilitated by spatial mass-loading profiles that indicate the locations of metal mass-loading, seasonal changes, and the extent of biogeochemical processes Mercury contamination from historic gold mines represents a potential risk to human health and the environment.
This fact sheet provides background information on the use of mercury in historic gold mining and processing operations in California, and describes a new USGS project that addresses the potential risks associated with mercury from these Acid drainage from abandoned coal mines is affecting thousands of miles of rivers in the eastern United States. Geological Survey USGS scientists are finding that neutral drainage is sometimes being mistaken for acidic drainage because both involve the formation of iron oxide-rich materials.
USGS scientists are adapting microbialYard drainage problems can wreak havoc on a garden or lawn, especially after a heavy rain. When you take steps to improve soil drainage, you can improve the overall health of your lawn and garden.
Most minor garden and lawn drainage issues are caused by clay soil.Improve Drainage in the Garden and Containers
A minor issue will be that you have standing water after a heavy rainfall for less than a day. Clay soil is more dense than sandy or loamy soil, and therefore, is slower to allow rainwater to filter through it. Minor yard drainage problems like this can usually be corrected by taking steps to improve clay soil. For more serious lawn and garden drainage problems, there are several things you can try to improve soil drainage. A more serious drainage issue means that you have standing water after light to moderate rainfall or if the standing water stays for more than a day.
These drainage issues can be caused by high water tables, low grading compared to surrounding properties, layers of hard materials like stone below the soil and extremely compacted soil. One solution for yard drainage issues is to create an underground drain. The most common underground drain is a French drain, which is essentially a ditch that is filled with gravel and then covered over. Drainage wells are another common underground solution for compacted soil or hard sub-layers that allows the water somewhere to run after rainfall.
Another way to improve soil drainage is to build up the soil where you are having the drainage issue or create a berm to redirect the water flow. This works best for garden drainage where specific beds may be getting flooded. Be aware, though, that when you build up a bed, the water will run somewhere else, which may create drainage issues elsewhere. Creating a pond or a rain garden has started to become popular as solutions for yard drainage problems.
Both of these solutions not only help collect excess rainwater, but also add a lovely feature to your landscape. Rain barrels are another thing that can be added to help with drainage.
Oftentimes, yards that have drainage problems not only have to deal with the rainwater that falls into the yard, but rainwater from nearby buildings as well. Rain barrels can be attached to downspouts and will collect rainwater that would normally run into the yard. This collected rainwater can then be used later when rainfall is low to water your yard. Yard drainage problems do not need to ruin your lawn or garden.Sustainable Soil Management. Departmentof Agriculture. These organizations do not recommend or endorse products, companies,or individuals.
ATTRA staffprefer to receive requests for information about sustainable agriculture via thetoll-free number Abstract Abstract: This publication covers basic soil properties andmanagement steps toward building and maintaining healthy soils. The publication isdivided into three distinct sections, each with its own purpose.
Section 1 dealswith basic soil principles and provides a understanding of living soils and how theywork. In section 1 you will find answers to why soil organisms and organic matterare important.
Section 2 covers management steps to build soil quality on your farm. The last section covers farmer stories of people who have successfully built up theirsoil.
A large resource section of other available information concludes the publication. Part I. Any farmer will tell you that a good soil: drains well and warms up quickly in the spring does not crust after planting soaks up heavy rains with little runoff stores moisture for drought periods has few clods and no hardpan resists erosion and nutrient loss supports high populations of soil organisms does not require increasing fertilizer for high yields has that rich, earthy smell produces healthy, high quality crops 1.
All these criteria indicate a soil that functions effectively today and will continueto produce long into the future. Creating soils with these characteristics can be accomplished by utilizing management practices that optimize the processes foundin native soils. Sustainable: the ability to keep in existence; maintain or prolong; to provide sustenance for. How does soil in its native condition function? How do forests and native grasslandsproduce plants and animals in the complete absence of fertilizer and tillage?
Whatare the principles by which these soils function? The answers to these questionsassure that the soil will be productive and profitable now and for future generations.Strictly speaking, the term data refers to measurements or observations, and the term information refers to results of analysis or synthesis of data.
Both data and information are needed for hydrologic studies, and the terms are used interchangeably here.
How does mine drainage occur?
To determine what data are needed, the designer must determine which hydrologic analysis method s will be used. The major task of a hydrology study is to compute design flow. There are conceptual methods and empirical methods for computation of design flow.
Conceptual methods in this category simulate, with a mathematical model, channel flow and watershed runoff processes. Movement and storage of water through the watershed are simulated at varying time and space scales, with varying degrees of complexity, omitting, including, or combining elements, depending on the model used and the requirements of the study.
Conceptual methods that TxDOT designers may use include the Rational method loosely classified as a conceptual method here and the hydrograph method. Like conceptual methods, empirical methods also use a mathematical relation that predicts the design flow, given properties of the watershed, channels, rainfall, or streamflow. However, the relationship does not represent explicitly the physical processes.
Instead, the relationships are derived with statistical analyses. Some analysts even refer to empirical methods as black box methods because the presentation of the process is not visible and obvious.
Empirical methods that TxDOT designers may use include flood frequency analysis of streamflow observations and regression equations. With flood frequency analysis, the empirical relationship predicts the design flow from statistical properties of the historical streamflow in the watershed.
With regression equations, the design flow is predicted with an equation that has been developed by correlating flows observed with watershed, channel, and rainfall properties. Data and information required for hydrologic analysis vary from method to method.
The conceptual methods require somewhat detailed information about the watershed and channel properties, whereas the empirical methods require streamflow data to establish the relationships and only limited data on watershed and channel properties to use the derived relationship.
Specific requirements for the different methods are called out in later sections of this Chapter, but broad categories of data required include the following:. All hydrologic analyses for TxDOT studies require collection of data about the geographic and geometric properties of the watershed. These data include, but are not limited to, the following:.
Data that describe the watershed properties are needed for the conceptual models, and to a limited extent, by certain empirical models. A conceptual model of watershed runoff, with components as illustrated in Figurerepresents processes of infiltration and overland flow. To do so, the model must be configured and calibrated with knowledge of the properties of the watershed that will affect infiltration and overland flow.
Those include:. These data are needed with conceptual models that do not seek to represent in great detail the physical processes. For example, with the rational methoda runoff coefficient relates runoff rate and rainfall rate. That coefficient is related to land use within the watershed.
And knowledge of land use, particularly knowledge of presence or absence of impervious area, is critical for assessing the applicability of regression equations. Channels, ponds, reservoirs, culverts, and other natural or constructed drainage features in a watershed affect the runoff from the watershed.
Thus data that describe those must be collected. For a conceptual model, data about the features are needed to make a decision about which model to use and configure the model appropriately.
For example, with a hydrograph methoddata describing channels are needed to select, calibrate, and use a routing method that accounts for the impact of a channel on the design flood peak. For an empirical model, data on drainage features is needed first to enable wise decisions about which model s to use, and second, to estimate model parameters. For example, flood frequency stream gauge analysis procedures require that the streamflow records be without significant regulation. To determine if this is so, the designer must have information on regulation in the watershed, including descriptions of ponds, reservoirs, detention structures, and diversions in the watershed.Water flowing across the land surface overland flow during or after a rainfall event.
Runoff: Surface and Overland Water Runoff
Water infiltrating into the soils or porous rock at the land surface during a rainfall event. Next Question. Can erosion of the land surface by flowing water occur if there is not enough rainfall to produce runoff?.
Yes B. No Next Question. What is necessary in order for Runoff to occur across the land surface? Rainfall events must be slow and gentle such that all precipitation infiltrates or soaks into the land surface or soils.
The duration of a rainfall event must be long enough, or produce a sufficient volume of precipitation to saturate the soils or rock at the land surface such that the excess water will flow overland across the land surface. Runoff is only possible after torrential downpours of rain. What is the definition of a drainage network or drainage system? A single river channel that flows across the land surface. A series of short unconnected stream segments or gullies that can be seen along a sloping land surface.
An integrated branching arrangement of smaller streams joining together to feed larger streams that then feed one or more main river channels. A random arrangement of streams that may or may not connect and that flow in seemingly random directions.
How long does it take a complex integrated drainage system such as those seen on the surface of the Earth and Mars to develop? The entire drainage system can develop within a few years. The entire drainage system can develop in short periods of time, essentially with in the time frame of a human life span. They can develop over the time span of a few centuries. They develop over long periods of geologic time, from thousands to millions of years.
They can compress time so that during a brief model run you can observe the evolution of a drainage system that would take place over long periods of geologic time. They allow you to explore and appreciate the effects of different factors on landform evolution by setting different parameter values C. They allow you to study the evolution of a drainage system in front of computer thus eliminate the need to do field work D.
Both A and B. When flowing water erodes the land surface to create a drainage network, do these drainages always develop at the same rate everywhere in nature or in a computer model?
The degree to which a surficial material is resistant to erosion by flowing water. Some rock types and soils are easily eroded and some are very resistant to erosion. The rate at which streams transport eroded sediments down slope or down stream. The degree of steepness for slopes and stream channels in a drainage system D. The change in slope from one portion of a drainage to another Next Question. The form of an entire drainage basin. The slope of the land surface. The process by which drainages form D.
Which of the following do you think would be the primary variable that controls the rate of drainage network development? Climate; including the amount of rainfall and the vegetation cover. The durability of the surface rock or soil and how easily it can be eroded. The steepness of the slope over which the streams flow and erode.
All of the above are primary or important variables. How do you think climate change would affect drainage morphology?Drainagein agriculturethe artificial removal of water from land; drainage is employed in the reclamation of wetlands, in the prevention of erosionand as a concomitant of irrigation in the agriculture of arid regions. A brief treatment of drainage follows. For full treatment, see irrigation and drainage. Drainage is an ancient practice, but apparently until recent times it was regarded as less important than irrigation.
The first drains were most likely ditches for channelling floodwaters back to the rivers. The addition of linings of less porous materials greatly improved drainage efficiency. The most significant 20th-century development in drainage technology was the application of land-grading techniques to facilitate uniform runoff.
Land may be smoothed with proper slopes and ditches so as to remove excess water before it enters the soil and thus prevent erosion, leaching of nutrients, and standing pools of water on the surface, and to permit early spring planting. If carefully planned, this smoothing also can prepare the land for surface irrigation, thus serving two purposes by one earth-moving operation.
After excess water enters the soil, its removal is an expensive and specialized undertaking that is not directly connected with irrigation, although it sometimes may be necessary for irrigated land. Modern drainage systems may be divided into two categories, surface and subsurface. The typical surface system consists of field drains, field ditches, a main collection ditch, and an outlet.
As the term implies, a surface system is designed to remove water that collects on top of the soil. Surface drainage is especially important for soils that absorb water slowly. The field drains vary in configuration according to topographyparallel drains being indicated for uniform surfaces and site-specific ones for areas of uneven accumulation.
Subsurface drainage systems consist of small conduitsa submain, a main, and an outlet. The conduits, equivalent to the field drains in a surface system, collect the water in the soil and drain it into the larger arteries. Factors determining the most efficient drainage system design for a particular property include soil type, land configuration, amount and pattern of rainfall, and types of crops to be grown.
Soils of high sand or silt content are generally suited to subsurface drainage, while soils of high clay content generally require surface systems. Article Media. Info Print Cite. Submit Feedback. Thank you for your feedback. Drainage agriculture. See Article History. Read More on This Topic. The planning and design of drainage systems is not an exact science. Although there have been many advances in soil and crop science, techniques….
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Although there have been many advances in soil and crop science, techniques have not been developed for combining the basic principles involved into precise designs. Irrigation and drainageartificial application of water to land and artificial removal of excess water from land, respectively. Some land requires irrigation or drainage before it is possible to use it for any agricultural production; other land profits from either practice to increase production.