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40-641: The Emajõgi is sometimes called the Suur Emajõgi (Big Emajõgi), in contrast with the Väike Emajõgi (Little Emajõgi), another river which flows into the southern end of Lake Võrtsjärv. The Emajõgi is the second-largest river in Estonia by discharge and the only fully navigable river. The source of the Emajõgi is at the northeastern shore of Võrtsjärv at Rannu-Jõesuu , from where the river follows

80-470: A lake or ocean. This would disrupt the ecosystem. Streamflow is one important route of water from the land to lakes and oceans. The other main routes are surface runoff (the flow of water from the land into nearby watercourses that occurs during precipitation and as a result of irrigation), flow of groundwater into surface waters, and the flow of water from constructed pipes and channels. Streamflow confers on society both benefits and hazards. Runoff downstream

120-403: A percentage of total runoff. Plotted on a graph, these data from the unit hydrograph for that storm, which represents the runoff added to the pre-storm baseflow. To forecast the flows in a large drainage basin using the unit hydrograph method would be difficult because in a large basin geographic conditions may vary significantly from one part of the basin to another. This is especially so with

160-422: A river to rise, peak, and fall in response to a storm. Once a rainfall-runoff relationship is established, then subsequent rainfall data can be used to forecast streamflow for selected storms, called standard storms. A standard rainstorm is a high intensity storm of some known magnitude and frequency. One method of unit hydrograph analysis involves expressing the hour by hour or day by day increase in streamflow as

200-438: A roughly eastward course towards Lake Peipus. The course of Emajõgi is divided into three distinct sections. In the upper course, from Võrtsjärv to Kärevere bridge, the river flows through large, flat and marshy areas, which are part of Alam-Pedja Nature Reserve . In this heavily meandering section, Emajõgi lacks a clearly defined floodplain – the flooded area spans several kilometres at times and has no definite borders. In

240-529: A slow recession . Because the peak flow also corresponds to the maximum water level reached during the event, it is of interest in flood studies. Analysis of the relationship between precipitation intensity and duration and the response of the stream discharge are aided by the concept of the unit hydrograph , which represents the response of stream discharge over time to the application of a hypothetical "unit" amount and duration of rainfall (e.g., half an inch over one hour). The amount of precipitation correlates to

280-408: A stream, a short term forecast of discharge can be made for a given rainstorm using a hydrograph. This method involves building a graph in which the discharge generated by a rainstorm of a given size is plotted over time, usually hours or days. It is called the unit hydrograph method because it addresses only the runoff produced by a particular rainstorm in a specified period of time—the time taken for

320-422: A variety of ways to measure the discharge of a stream or canal. A stream gauge provides continuous flow over time at one location for water resource and environmental management or other purposes. Streamflow values are better indicators than gage height of conditions along the whole river. Measurements of streamflow are made about every six weeks by United States Geological Survey (USGS) personnel. They wade into

360-489: A waterway and trade route for centuries. In the past, it has also been an obstacle for land transport between Northern and Southern Estonia, because the river flows in a low-lying and swampy valley. Of the few suitable locations for crossing the river, Tartu has the most favourable conditions. Due to its location on the crossing of land and water routes, Tartu became an important trading center in Ancient Estonia . In

400-407: Is a means to collect water for storage in dams for power generation of water abstraction. The flow of water assists transport downstream. A given watercourse has a maximum streamflow rate that can be accommodated by the channel that can be calculated. If the streamflow exceeds this maximum rate, as happens when an excessive amount of water is present in the watercourse, the channel cannot handle all

440-399: Is a measure of the quantity of any fluid flow over unit time. The quantity may be either volume or mass. Thus the water discharge of a tap (faucet) can be measured with a measuring jug and a stopwatch. Here the discharge might be 1 litre per 15 seconds, equivalent to 67 ml/second or 4 litres/minute. This is an average measure. For measuring the discharge of a river we need a different method and

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480-536: Is good for environment, as stagnant water does not stay fresh and inviting very long. There are many factors, both natural and human-induced, that cause rivers to continuously change: Natural mechanisms Human-induced mechanisms Streamflow is measured as an amount of water passing through a specific point over time. The units used in the United States are cubic feet per second , while in most other countries cubic meters per second are utilized. There are

520-450: Is straightened, a line can be ruled drawn through the points. A projection can then be made by extending the line beyond the points and then reading the appropriate discharge for the recurrence interval in question. Runoff of water in channels is responsible for transport of sediment , nutrients , and pollution downstream. Without streamflow, the water in a given watershed would not be able to naturally progress to its final destination in

560-416: Is the sum of processes within the hydrologic cycle that increase the water levels of bodies of water. Most precipitation occurs directly over bodies of water such as the oceans, or on land as surface runoff . A portion of runoff enters streams and rivers, and another portion soaks into the ground as groundwater seepage . The rest soaks into the ground as infiltration, some of which infiltrates deep into

600-404: Is typically expressed in units of cubic meters per second (m³/s) or cubic feet per second (cfs). The catchment of a river above a certain location is determined by the surface area of all land which drains toward the river from above that point. The river's discharge at that location depends on the rainfall on the catchment or drainage area and the inflow or outflow of groundwater to or from

640-535: The Rhine river in Europe is 2,200 cubic metres per second (78,000 cu ft/s) or 190,000,000 cubic metres (150,000 acre⋅ft) per day. Because of the difficulties of measurement, a stream gauge is often used at a fixed location on the stream or river. A hydrograph is a graph showing the rate of flow (discharge) versus time past a specific point in a river, channel, or conduit carrying flow. The rate of flow

680-470: The aquifers underground full of water by discharging water downward through their streambeds. In addition to that, the oceans stay full of water because rivers and runoff continually refreshes them. Streamflow is the main mechanism by which water moves from the land to the oceans or to basins of interior drainage . Stream discharge is derived from four sources: channel precipitation, overland flow, interflow, and groundwater. Rivers are always moving, which

720-471: The cross-sectional area (in m or ft ). It includes any suspended solids (e.g. sediment), dissolved chemicals like CaCO 3 (aq), or biologic material (e.g. diatoms ) in addition to the water itself. Terms may vary between disciplines. For example, a fluvial hydrologist studying natural river systems may define discharge as streamflow , whereas an engineer operating a reservoir system may equate it with outflow , contrasted with inflow . A discharge

760-498: The 19th century, Emajõgi was actively used for transporting different cargo to Tartu – firewood , timber , hay , fish, and so on. The main type of vessel used was the lodi , a small river barge or sailing ship adjusted for navigation on Lake Peipus and Emajõgi. Up to 200 barges were anchored in Tartu's port at the time. The first steam paddler appeared on Emajõgi in 1843; there were six by 1900. The last river barges disappeared by

800-559: The Hydrological Division of the USGS for large streams. For a basin with an area of 5,000 square miles or more, the river system is typically gauged at five to ten places. The data from each gauging station apply to the part of the basin upstream that location. Given several decades of peak annual discharges for a river, limited projections can be made to estimate the size of some large flow that has not been experienced during

840-399: The area, stream modifications such as dams and irrigation diversions, as well as evaporation and evapotranspiration from the area's land and plant surfaces. In storm hydrology, an important consideration is the stream's discharge hydrograph, a record of how the discharge varies over time after a precipitation event. The stream rises to a peak flow after each precipitation event, then falls in

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880-408: The bridges, the only operating cable ferry in Estonia crosses the river at Kavastu , about 10 kilometres (6.2 mi) downstream of Luunja bridge. Discharge (hydrology) In hydrology , discharge is the volumetric flow rate (volume per time, in units of m /h or ft /h) of a stream . It equals the product of average flow velocity (with dimension of length per time, in m/h or ft/h) and

920-485: The corresponding discharge from the rating curve. If a continuous level-recording device is located at a rated cross-section, the stream's discharge may be continuously determined. Larger flows (higher discharges) can transport more sediment and larger particles downstream than smaller flows due to their greater force. Larger flows can also erode stream banks and damage public infrastructure. G. H. Dury and M. J. Bradshaw are two geographers who devised models showing

960-418: The discharge of a river is based on a simplified form of the continuity equation . The equation implies that for any incompressible fluid, such as liquid water, the discharge (Q) is equal to the product of the stream's cross-sectional area (A) and its mean velocity ( u ¯ {\displaystyle {\bar {u}}} ), and is written as: where For example, the average discharge of

1000-482: The distribution of rainfall because an individual rainstorm rarely covers the basin evenly. As a result, the basin does not respond as a unit to a given storm, making it difficult to construct a reliable hydrograph. For large basins, where unit hydrograph might not be useful and reliable, the magnitude and frequency method is used to calculate the probability of recurrence of large flows based on records of past years' flows. In United States, these records are maintained by

1040-470: The end of the middle course near Kavastu. In the lower course, the river flows through a swampy lowland – Emajõe Suursoo – before emptying into Lake Peipus at Praaga . The length of the river is 100 kilometres (62 mi). In 1927, its length was measured to be 117 kilometres (73 mi). This may have changed somewhat in the 1930s, when the river's meandering upper course was straightened to allow for easier navigation. The Emajõgi has been widely used as

1080-433: The ground to replenish aquifers. Streamflow Streamflow , or channel runoff , is the flow of water in streams and other channels , and is a major element of the water cycle . It is one runoff component, the movement 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

1120-712: 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. Streams play a critical role in the hydrologic cycle that is essential for all life on Earth. A diversity of biological species, from unicellular organisms to vertebrates, depend on flowing-water systems for their habitat and food resources. Rivers are major aquatic landscapes for all manners of plants and animals. Rivers even help keep

1160-424: The level of the stream is described by a rating curve . Average velocities and the cross-sectional area of the stream are measured for a given stream level. The velocity and the area give the discharge for that level. After measurements are made for several different levels, a rating table or rating curve may be developed. Once rated, the discharge in the stream may be determined by measuring the level, and determining

1200-552: The mid-20th century, however several new ships were brought onto the river to continue naval transport to Pskov , Piirissaar and other destinations. Fast hydrofoils , which were first introduced in 1960s, operated daily on the Tartu-Pskov route. Traffic on the route ended in 1992. Though attempts have been made to restart it since 1997, it remains closed. Emajõgi is crossed by 10 bridges, the majority of them located in Tartu. The bridges are, in downstream order: In addition to

1240-412: The middle course from Kärevere to Kavastu through Tartu, Emajõgi follows a straighter course and flows in a clearly defined, shallow valley mostly a maximum of 10 m (33 ft) deep. The width of the valley in the middle course is 1–1.5 km (0.62–0.93 mi); in Tartu, it narrows to 800 m (2,600 ft). The narrowest section of the valley (400–600 km (250–370 mi)) is located in

Emajõgi - Misplaced Pages Continue

1280-577: The most common is the 'area-velocity' method. The area is the cross sectional area across a river and the average velocity across that section needs to be measured for a unit time, commonly a minute. Measurement of cross sectional area and average velocity, although simple in concept, are frequently non-trivial to determine. The units that are typically used to express discharge in streams or rivers include m /s (cubic meters per second), ft /s (cubic feet per second or cfs) and/or acre-feet per day. A commonly applied methodology for measuring, and estimating,

1320-403: The period of record. The technique involves projecting the curve (graph line) formed when peak annual discharges are plotted against their respective recurrence intervals. However, in most cases the curve bends strongly, making it difficult to plot a projection accurately. This problem can be overcome by plotting the discharge and/or recurrence interval data on logarithmic graph paper. Once the plot

1360-583: The relationship between discharge and other variables in a river. The Bradshaw model described how pebble size and other variables change from source to mouth; while Dury considered the relationships between discharge and variables such as stream slope and friction. These follow from the ideas presented by Leopold, Wolman and Miller in Fluvial Processes in Geomorphology . and on land use affecting river discharge and bedload supply. Inflow

1400-412: The stream flow termed the orange method or float method is: In the United States, streamflow gauges are funded primarily from state and local government funds. In fiscal year 2008, the USGS provided 35% of the funding for everyday operation and maintenance of gauges. Additionally, USGS uses hydrographs to study streamflow in rivers. A hydrograph is a chart showing, most often, river stage (height of

1440-661: The stream to make the measurement or do so from a boat, bridge, or cableway over the stream. For each gaging station, a relation between gage height and streamflow is determined by simultaneous measurements of gage height and streamflow over the natural range of flows (from very low flows to floods). This relation provides the streamflow data from that station. For purposes that do not require a continuous measurement of stream flow over time, current meters or acoustic Doppler velocity profilers can be used. For small streams—a few meters wide or smaller— weirs may be installed. One informal method that provides an approximation of

1480-420: The volume of water (depending on the area of the catchment) that subsequently flows out of the river. Using the unit hydrograph method, actual historical rainfalls can be modeled mathematically to confirm characteristics of historical floods, and hypothetical "design storms" can be created for comparison to observed stream responses. The relationship between the discharge in the stream at a given cross-section and

1520-471: The water above an arbitrary altitude) and streamflow (amount of water, usually in cubic feet per second). Other properties, such as rainfall and water quality parameters can also be plotted. For most streams especially those with a small watershed, no record of discharge is available. In that case, it is possible to make discharge estimates using the rational method or some modified version of it. However, if chronological records of discharge are available for

1560-543: The water, and flooding occurs. The 1993 Mississippi river flood , the largest ever recorded on the river, was a response to a heavy, long duration spring and summer rainfalls. Early rains saturated the soil over more than a 300,000 square miles of the upper watershed, greatly reducing infiltration and leaving soils with little or no storage capacity. As rains continued, surface depressions, wetlands, ponds, ditches, and farm fields filled with overland flow and rainwater. With no remaining capacity to hold water, additional rainfall

1600-560: Was forced from the land into tributary channels and thence to the Mississippi River . For more than a month, the total load of water from hundreds of tributaries exceeded the Mississippi's channel capacity, causing it to spill over its banks onto adjacent floodplains. Where the flood waters were artificially constricted by an engineered channel bordered by constructed levees and unable to spill onto large section of floodplain,

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