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Channel roughness
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Rivers key terms v2
| Question | Answer |
|---|---|
| Braiding | Sub-dividing of a river channel, a characteristic of a river with variable discharge. |
| Channel roughness | Measurement of the smoothness of the wetted perimeter and the extent to which rocks protrude into the flow of a river. A smooth profile will result in little turbulence and a high velocity. |
| Corrosion | river erosion whereby transported particles grind away at the river bed and banks. |
| Deltas | And area of deposition (usually mud and sand) at the mouth of a river. Two common types of delta are arcuate (eg. Nile) and bird's foot (eg. Mississippi). |
| Discharge | The volume of water passing a given point in a given period of time,usually expressed in cumecs (cubic metres per second) and calculated as: cross sectional area x velocity. |
| Drainage basin | Area of land, bordered by a watershed, drained by a river and its tributaries. |
| Flooding | Inundation of land not normally under water, eg. river floodplain. |
| Floodplains | Extensive, flat land immediately adjacent to a river that is prone to periodic inundation. |
| Gorge | Steep-sided narrow valley often found immediately downstream from a waterfall. |
| Graded profile | Smooth concave long profile of a river that has achieved a state of equilibrium with its environment. |
| Hard engineering | Commonly, built structures such as concrete walls designed to resist natural processes. |
| Hjulstrom curve | graph showing the relationship between the velocity of a river and the critical velocity needed to pick up (erode) or deposit an individual particle. The graph comprises two curves, showing the critical erosion velocity+the critical deposition velocity. |
| Hydraulic action | River erosion involving the sheer force of flowing water. |
| Hydraulic radius | Measure of channel efficiency calculated as cross-sectional area / wetted perimeter. The higher the value, the greater the efficiency (less energy lost by friction with bed and banks) of the channel. |
| Incised meander | Steep-sided meander formed during a period of significant down-cutting following rejuvenation. |
| Kinetic energy | When water moves downhill, potential energy is converted to kinetic energy and used to do'work'. |
| Knick point | Point in the river's long profile, often marked by a waterfall, that represents the extent to which a river has re-graded its profile following rejuvenation. Over time a knick point will gradually migrate upstream due to waterfall retreat. |
| Levees | Raised river banks formed by deposition when, in flood, a river spills over the sides of its channel. |
| Magnitude-frequency analysis | Analysis of the magnitude and frequency of events such as floods, which are often characterised by 'high magnitude, low frequency' events (negative association). |
| Meander | Sweeping bend or curve in a river, characterised by having a depositional slip-off slope on the inside bend and an erosional river cliff on the outside bend. |
| Potential energy | stored energy in a still body of water that has potential to do 'work'. |
| Pothole | circular hollow or depression formed by erosion in bedrock on a river bed. |
| Rapids | Series of relatively small 'steps' in the long profile of a river forming a stretch of turbulent white water. |
| Rejuvenation | renewed period of river erosion resulting from a fall in base level (often sea level). As the river cuts down into its channel characteristic features form including incised meanders and river terraces. |
| River restoration | restoring a river channel to its natural course following earlier intervention, eg. channel straightening. River restoration usually involves soft engineering and aims to improve natural habitats and the amenity value of the river. |
| River terrace | Abandoned floodplain left perched above the current floodplain following a renewed period of eroding (rejuvenation). |
| Salinisation | the deposit of salts on or close to the ground surface commonly associated with high rates of evaporation in arid environments. |
| soft engineering | management approaches that have minimal impacts on the environment and aim tow work with natural processes (e.g. planting trees in a river basin to reduce the risk of flooding) |
| Solution | Dissolving of chemicals as water flows over soluble rocks. |
| Storm hydrograph | Line graph showing the discharge of a river over a period of time as it responds to an individual storm event. |
| Velocity | speed of flow of a river. The line of fastest flow in a river is called the thalweg. |
| Water balance | Audit of water based on the equation: precipitation = runoff + evapotranspiration +/- soil moisture. |
| Waterfall | 'Step' in the long profile of a river characterised by water cascading over a rock lip into a deep plunge pool. |
| Wetted perimeter | Length (in metres) of river channel in contact with water at a river cross-section. |
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apeploe
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