The total volume of water that leaves a watershed as streamflow over the course of a year. The majority of these investigations have been conducted in tiny research catchments (less than 1 km.sup.2) but some large-scale studies have also been done.
Catchment-scale studies can provide information about the relationship between land use and streamflow that is not available from smaller-scale investigations. They can also indicate potential problems with groundwater management if significant flows are found to come from surface sources.
In general, the more impervious (dirt or concrete) the land cover within the study area, the lower the estimated yield will be. Forested areas often have water yields higher than agricultural lands because they retain more precipitation. Urban areas tend to have very low water yields because they are dominated by impervious surfaces such as streets and roofs which prevent rainwater from percolating into the ground. Streams in urban areas generally carry only filtered sunlight and heat energy imparted to them by winds. This is different from streams in rural or suburban areas where they usually contain some small amount of runoff from surrounding properties.
Water yields can also be affected by climate change. For example, rainfall patterns may change due to environmental effects like increased atmospheric temperature or changes in land use.
Water yield is computed by dividing the mean annual volume of streamflow generated in a nested watershed (in cubic meters per year) by the nested watershed's area (expressed in square kilometers). Water yield is defined as the average yearly volume of streamflow (produced in a nested watershed) divided by the area of that same nested watershed.
The water yield for a given site cannot be directly observed because most sites are not monitored by sensors that measure streamflow continuously. Instead, scientists use statistical methods to estimate the average monthly or annual flow from short-term observations made at different times of the year. They do this by relating the number of observations that exceed certain threshold levels of flow to samples taken over time. For example, if there were an observation every month of the year except July, then the total annual flow would be estimated by adding up all of the months' yields and dividing it by 12.
Scientists use the term "yield" to describe the amount of water that flows out of a watershed into adjacent areas when it is significantly affected by upstream developments. Yields can also be described as the capacity of a watershed to produce fluid volumes greater than some minimum threshold level. For example, the annual yield of a river is the average volume of runoff that flows down its channel each year. The more developed the surrounding land, the less likely it is to affect the rate at which it receives precipitation and thus the lower its annual yield will be.
Water yield is defined as the discharge of a stream at a specific cross section determined during a specified time period: a day, a month, a season, or a year, or a series of such intervals. The term is used to describe the amount of water that flows from a reservoir or other storage area into another body of water or channel system. It includes the water that runs off from land and pools in gullies, canyons, or other low-lying areas near the source of a stream; this water would not be available for other uses unless it was also included in the estimate of water supply.
The United States Bureau of Reclamation estimates the annual water yield from the Colorado River system at about 170 billion gallons. The actual yield will vary depending on such factors as rainfall, snowmelt, streamflow, and soil moisture content.
When you use the word "yield" in relation to plants, it means the amount of fruit or seeds produced by a single plant or crop field. For example, if a farmer has 100 acres of apples and only 50 of them bear fruit, then the yield is 50%. In the case of water, the term means the quantity of liquid that flows from a reservoir or other storage area into another body of water or channel system.
The material eroded from the whole region drained by a stream and its tributaries is carried by all of the water that reaches it and its tributaries. Sediment yield refers to the total quantity of erosional material exported from a drainage basin. It can be calculated by multiplying the average annual rate of sediment yield by the area of the drainage basin.
Sediment supply is the term used to describe the amount of sediment entering a river system relative to its capacity to carry it. The main source of sediment for most rivers is the erosion of upland areas through rainfall and snowmelt. Other major sources include glaciers, lava flows, and coastal erosion. A river's ability to transport sediment depends on many factors such as its size, shape, depth, and the type of soil it carries.
Sediment transport is the term used to describe the movement of sediment in a river system. It can be divided into two processes: suspended sediment transport, which includes silt and clay particles that are held together by surface tension or electrostatic charges; and bedload transport, which includes large rock fragments that are transported by the force of water flowing over them.
Suspended sediment transport has several important effects on aquatic ecosystems. It can change the color of waters by adding organic matter that is decomposed by bacteria.
The amount of sediment reaching or passing a site of interest in a particular period of time is characterized as "sediment yield," which is represented in m3/yr or t/yr. When considering the drainage basin's surface, the measurement is t/km2/yr. A common unit for reporting sediment yields is mg/m2/year. Values may be reported for an entire river system or for individual streams within that system.
Sediment yields can be divided into two categories: dry-season yield and wet-season yield. Dry-season yields are estimated when there has been no recent precipitation and no water flows are present. Wet-season yields occur when it has recently rained and stream levels are high. Satellite images often show clear differences between dry- and wet-season conditions with bare ground indicating no rain and green vegetation showing recent rainfall.
Dry-season yields are useful for estimating the impact of human activities such as mining or logging since these events do not affect water quality or quantity. Wet-season yields are used to estimate the effect of natural processes like flood erosion or snowmelt. Both types of yields are important for understanding how much sediment enters our lakes and oceans which could have environmental impacts if not removed.
Individual stream sediment yields range from less than 1 millimeter per year (mm/yr) to more than 10 meters per year (meters/yr).
Water yield evaluation gives trustworthy information on the availability of water resources (surface and ground water) for planning extraction and usage. This may be quite helpful when organizing water-related activities. It depicts the interplay of surface and groundwater in the watershed. Yield assessments provide information about the amount of water available to meet future needs as well as identifying opportunities to improve management practices that can increase supply or reduce demand.
Water yield is the amount of water that flows from a river basin to its ocean or other bodies over time. It is usually expressed in cubic meters per second (m3/s). The term "water yield" can also refer to the total volume of water produced by a reservoir or aquifer during a given time period. This volume must then be divided by the area of influence of the reservoir to obtain the average rate of infiltration at which the reservoir is filling up (if not all of this water is being released into rivers, streams, or other bodies of water).
Water yield assessments involve collecting flow data at several locations within the basin and using these measurements to build a picture of how much water is flowing into and out of the basin. The location where the most flow is recorded determines the geographic center of the basin. From this point, a line is drawn east and west until it intersects another stream or body of water. The length of this line is called the basin perimeter.