WEBVTT 00:00:00.500 --> 00:00:03.975 Welcome to GCSE A Q A Geography revision. 00:00:04.125 --> 00:00:07.489 Topic G 11: River landscapes in the UK. 00:00:07.639 --> 00:00:09.623 This is an optional topic. 00:00:09.773 --> 00:00:13.024 Study it if it is one of the options taught by your school. 00:00:13.174 --> 00:00:18.027 Use your school’s selected case studies if they differ from these revision examples. 00:00:20.700 --> 00:00:24.675 A river's long profile shows how height changes from source to mouth. 00:00:24.825 --> 00:00:30.509 It is usually steep near the source and becomes gentler downstream, giving a broadly concave shape. 00:00:33.167 --> 00:00:36.875 In the upper course, vertical erosion deepens a narrow valley. 00:00:37.025 --> 00:00:42.707 Farther downstream, lateral erosion widens it, and a broader floodplain commonly develops. 00:00:45.367 --> 00:00:50.415 Channel width, depth and discharge generally increase downstream as tributaries join. 00:00:50.565 --> 00:00:57.337 The bedload often becomes smaller and rounder through attrition and sorting, although local conditions can interrupt these trends. 00:01:00.000 --> 00:01:03.294 Hydraulic action is erosion by the force of water. 00:01:03.444 --> 00:01:07.281 Abrasion is the bed and banks being worn by transported sediment. 00:01:07.431 --> 00:01:11.650 Attrition makes transported particles smaller and rounder as they collide. 00:01:14.300 --> 00:01:17.317 Solution dissolves soluble minerals in rocks. 00:01:17.467 --> 00:01:23.067 Vertical erosion cuts down into the bed; lateral erosion attacks the banks and widens a valley. 00:01:25.733 --> 00:01:28.528 Traction rolls large particles along the bed. 00:01:28.678 --> 00:01:36.783 Saltation bounces smaller particles; suspension carries fine sediment in the water; solution carries dissolved substances. 00:01:39.433 --> 00:01:44.090 Deposition occurs when a river loses the energy needed to carry some of its sediment. 00:01:44.240 --> 00:01:49.551 This can happen when flow slows on a floodplain, enters still water or discharge falls. 00:01:52.233 --> 00:01:58.173 Interlocking spurs form where a river winds around projecting hillsides while mainly eroding downwards. 00:01:58.323 --> 00:02:02.509 Weathering and mass movement help create the steep sides of a V-shaped valley. 00:02:05.167 --> 00:02:09.912 A waterfall can develop where resistant rock overlies less resistant rock. 00:02:10.062 --> 00:02:17.016 Faster erosion of the softer rock creates a step and a plunge pool; abrasion and hydraulic action enlarge the pool. 00:02:19.667 --> 00:02:23.412 Undercutting leaves an unsupported overhang, which collapses. 00:02:23.562 --> 00:02:28.670 Repeated collapse makes the waterfall retreat upstream, leaving a steep-sided gorge. 00:02:28.820 --> 00:02:30.505 Waterfall retreat. 00:02:30.655 --> 00:02:33.554 Undercutting and collapse move the falls upstream. 00:02:33.704 --> 00:02:38.663 The diagram simplifies the rock structure and is not a measured section of High Force. 00:02:43.333 --> 00:02:48.282 At a meander, faster flow near the outside bend causes erosion and a river cliff. 00:02:48.432 --> 00:02:53.264 Slower flow near the inside bend deposits sediment, building a slip-off slope. 00:02:53.414 --> 00:02:56.485 Helical flow helps move sediment across the channel. 00:02:59.167 --> 00:03:01.533 Erosion can narrow a meander neck. 00:03:01.683 --> 00:03:08.765 During high flow the river may cut through, taking a shorter route; deposition blocks the old loop's ends, leaving an ox-bow lake. 00:03:11.433 --> 00:03:16.297 Floodplains develop through lateral channel movement and deposition during floods. 00:03:16.447 --> 00:03:20.145 Repeated flooding leaves layers of sediment across the valley floor. 00:03:22.800 --> 00:03:25.828 Natural levées are raised banks beside a channel. 00:03:25.978 --> 00:03:34.777 When floodwater spills over, it slows and deposits coarser material first near the banks, while finer material travels farther across the floodplain. 00:03:37.433 --> 00:03:41.767 An estuary is the tidal mouth of a river where freshwater meets seawater. 00:03:41.917 --> 00:03:47.077 Tides, river flow and sediment deposition can create mudflats and salt marshes. 00:03:49.733 --> 00:03:56.111 A flood occurs when water covers land normally dry, often because discharge exceeds channel capacity. 00:03:56.261 --> 00:04:02.032 Discharge is the volume of water passing a point each second, measured in cubic metres per second. 00:04:04.700 --> 00:04:07.866 Heavy or prolonged rain increases water input. 00:04:08.016 --> 00:04:15.673 Saturated ground, frozen ground or impermeable rocks reduce infiltration, sending more water rapidly towards channels. 00:04:18.333 --> 00:04:20.808 Steep slopes encourage rapid runoff. 00:04:20.958 --> 00:04:28.370 Urban surfaces and drains can speed water into rivers; removing vegetation can reduce interception and water storage. 00:04:31.033 --> 00:04:35.195 A storm hydrograph shows river discharge changing after rainfall. 00:04:35.345 --> 00:04:41.402 Peak discharge is the highest flow, and lag time is the time between peak rainfall and peak discharge. 00:04:41.552 --> 00:04:43.600 Rainfall and river response. 00:04:43.750 --> 00:04:48.134 Bars show relative rainfall and the line shows relative discharge. 00:04:48.284 --> 00:04:53.180 There are no numerical units because these are separate normalised schematic series. 00:04:57.833 --> 00:05:03.783 A short lag time and high peak often indicate a rapid catchment response and greater flood risk. 00:05:03.933 --> 00:05:10.585 Basin size, shape, rainfall pattern and antecedent conditions (how wet it was beforehand) also matter. 00:05:13.267 --> 00:05:17.225 Dams and reservoirs can store floodwater and release it gradually. 00:05:17.375 --> 00:05:24.688 They may also supply water or electricity, but are costly, flood land and alter downstream sediment and habitats. 00:05:27.367 --> 00:05:35.259 Channel straightening can move water through a location faster, but may increase flood risk downstream and reduce habitat diversity. 00:05:37.933 --> 00:05:41.577 Embankments increase the amount of water held within a channel. 00:05:41.727 --> 00:05:46.474 They need maintenance, and failure or overtopping can cause dangerous flooding. 00:05:49.133 --> 00:05:53.321 Flood relief channels divert some flow away from vulnerable areas. 00:05:53.471 --> 00:05:58.559 They require land and careful design so they do not shift risk to another community. 00:06:01.233 --> 00:06:06.637 Flood warnings and preparation help people move belongings, evacuate or use barriers. 00:06:06.787 --> 00:06:12.791 Warnings reduce harm but do not prevent the river from rising, and people need time and support to act. 00:06:15.467 --> 00:06:19.549 Floodplain zoning limits vulnerable development in high-risk areas. 00:06:19.699 --> 00:06:26.823 It avoids future exposure but can restrict building opportunities and does not protect existing homes by itself. 00:06:29.500 --> 00:06:35.174 Planting trees can increase interception, infiltration and surface roughness, slowing some runoff. 00:06:35.324 --> 00:06:42.075 Its effectiveness depends on location and storm conditions; it cannot guarantee protection from every extreme flood. 00:06:44.733 --> 00:06:50.268 River restoration can reconnect a river with its floodplain and create space to store water. 00:06:50.418 --> 00:06:55.409 It can benefit habitats but may require changes in land use and compensation. 00:06:58.067 --> 00:07:02.496 Evaluate a scheme using social, economic and environmental effects. 00:07:02.646 --> 00:07:09.365 Ask which places gain protection, whether risk moves elsewhere, and how costs and benefits change over time. 00:07:12.033 --> 00:07:17.205 The River Tees rises on the eastern side of the Pennines and flows towards the North Sea. 00:07:17.355 --> 00:07:24.063 Upper Teesdale has steep valley sections and waterfalls, while the lower river has broader lowland areas and an estuary. 00:07:26.733 --> 00:07:32.493 At High Force, the Tees flows over resistant Whin Sill dolerite above older sedimentary rocks. 00:07:32.643 --> 00:07:37.240 Erosion creates the waterfall and gorge, and the falls retreat over time. 00:07:37.390 --> 00:07:41.206 Real geology is more complex than a two-layer textbook sketch. 00:07:43.867 --> 00:07:47.225 Near Yarm, bends illustrate meandering in the lower valley. 00:07:47.375 --> 00:07:55.597 Lateral erosion and deposition help move bends over time; nearby floodplain land is exposed when river levels exceed capacity. 00:07:58.267 --> 00:08:03.752 At Teesmouth, river sediment, tides and marine processes shape mudflats and salt marsh. 00:08:03.902 --> 00:08:10.963 Industrial development and management also influence the modern estuary, so it is not an untouched natural landscape. 00:08:13.633 --> 00:08:21.526 The Jubilee flood relief channel opened in 2002 as part of the Maidenhead, Windsor and Eton flood alleviation scheme. 00:08:21.676 --> 00:08:27.360 It addresses flood risk from the Thames to homes, businesses and infrastructure in these communities. 00:08:30.033 --> 00:08:33.185 The channel is 11.6 kilometres long. 00:08:33.335 --> 00:08:39.861 Gates at Taplow divert some Thames water through it during high flows; the water rejoins the Thames at Datchet. 00:08:40.011 --> 00:08:43.944 The wider scheme reduces risk to about 3,000 properties. 00:08:46.600 --> 00:08:52.061 Lower flood risk benefits households and businesses and reduces potential disruption. 00:08:52.211 --> 00:08:59.122 Building and maintaining the channel has substantial costs, and protection is limited by the scheme's design and capacity. 00:09:01.800 --> 00:09:08.305 The channel includes naturalistic habitats and paths, providing environmental and recreational benefits. 00:09:08.455 --> 00:09:14.359 Gates, weirs and channel works still modify flows and require ecological care and maintenance. 00:09:17.033 --> 00:09:22.643 Communities outside the scheme remain at risk, creating questions about how investment is shared. 00:09:22.793 --> 00:09:29.001 The Environment Agency states that the Jubilee does not adversely affect upstream or downstream communities; 00:09:29.151 --> 00:09:33.641 do not present downstream flood damage as proof that the channel caused it. 00:09:36.300 --> 00:09:46.763 This example shows why social, economic and environmental evaluation matters: protection, cost, access, habitats and the limits of coverage all need consideration. 00:09:49.433 --> 00:09:52.057 That completes River landscapes in the UK. 00:09:52.207 --> 00:09:55.553 Revisit the notes and test yourself on the revision website.