(Options) Freshwater Case Studies Flashcards
1
Q
Sediment Budgets / Sediment and Channel Changes 1
A
Huang He / Yellow River, China
- High sediment load (average sediment concentration 37kg/m3, peak flows may reach 900kg/m3) due to flowing through Loess Plateau of Central China (easily eroded by water)
- large load = problems for dam/reservoir management downstream and people living in floodplain area where flooding common
- 24% sediment reaches sea, 33% deposited floodplain, 43% deposited delta area
- Sanmexia dam (1960) reservoir capacity reduced over 1/3 by 1964 due to sediment rich river water
2
Q
Sediment Budgets / Sediment and Channel Changes 2
A
River Nile, (Egypt primarily but many countries)
- Average sediment load 1.4kg/m3 (doesn’t flow through areas of such easily eroded material)
- Before dam = 130mn tonnes silt carried in Nile - 10% deposited floodplain, 90% delta area/ flowed into Mediterranean sea - now silt collects behind Aswan Dam (built 1968) and amount carried by Nile is reduced
- Aswan Dam = floodplains no longer receive annual input of nutrients = many farmers now have to buy artificial fertilisers to maintain crop yields
- Aswan Dam = loss of fertile agricultural land in its delta region
- Sardine catches in Mediterranean Sea reduced as many nutrients formerly available to the fish are retained within the sediment behind the dam
3
Q
Deltas affected by reduction in sediment supply Examples
A
Ganges Delta (Bangladesh) Mississippi Delta (USA)
4
Q
Flood Alleviation Hard Engineering
A
Malton
- River Derwent
- 1999 floods 140 homes and 40 businesses flooded
- 2004 £9mn flood defence scheme (special status) - design £1.5mn, construction £7.5mn
- protect against 1 in 50yr event (2% chance yr)
- Flood walls + artificial levees - embankments made of clay from local wetlands (special embankment where railway / river close)
- water-level pressure probes / monitors alert EA staff / automatic systems close valves
5
Q
Flood Alleviation Soft Engineering
A
Pickering
- River Derwent - Pickering Beck
- topography = flashy response (flat moorland w/ large precipitation, steep valley sides)
- 2007 = 85 properties and main A170 flooded
- 2010 ‘slowing the flow’ (land management and reduction peak flow)
- DEFRA fund 1/3 £750,000 budget
- 1/3 land public ownership = easy instigate
- pop. 7,270
- Durham uni computer model work out where intervene
- plant 50ha native woodland
- woody debris dams (force water onto floodplain until flow slow) - 100 dams planned
- education (farmers/landowners manage land) - drop in sessions locals
- no-burn buffer zones
- monitoring stations and gauges
- 1-2m embankments force water onto upstream unused floodplain
6
Q
Flood Defences
A
R. Medway, Tonbridge
- flood 1968 97mm rain 16hrs = £1.5mn damage
- prone to flooding clay geology, urbanised
- flood wall 1m town - promenade
- Gabion boxes, revetments
- land use zoning - not built up by river
- flood proof buildings (ground floor = car park)
- Park = washlands / floodplain
- Leigh flood barrier 1970 £3.6mn, store 5.5mn m3 + water
7
Q
Flooding
A
Bangladesh
- vulnerable to climate change - sea level rise and extreme weather
- poor
- rapid pop. growth 2.7% per annum
- monsoonal (75% annual rainfall June-Sept), snow/glacier melt Himalayas, steep slopes (high runoff meghalaya hills), overpopulated floodplain, deforestation, storm surge (coastal floods), urbanisation
- high pop. density = over 1,000 ppl per km2
- high peak discharge rivers = 100,000 cumbers Brahmaputra (June/July flooding and agricultural land destroyed)
- large quantities sediment
- building embankments = back-flooding (humans worsen) and deposition increase
- few metres asl
- up to 80% country on delta
- monsoon = 30-50% country flooded - flooding = fish (75% dietary protein and over 10% annual export earning)
- 1998 flood: over 2/3 country flooded, 4750 died, 23mn homeless, 130,000 cattle died, 660,000 hectares crop destroyed, 400 factories closed, 11,000km roads damaged, 1,000 schools damaged / destroyed
8
Q
Dam 1
A
Three Gorges Dam, China
- Yangtze River: source = Himalayas, severe flooding every 10yrs, last 1998 (area size NZ flooded + $30bn damage), C20th over 300,000 died by floods
- Advantages: Control flooding downstream = protects large settlements, water for irrigation and urban areas (reservoir stores up to 5mn gallons), 84 terawatt-hours annually, HEP meets 15% china’s energy demand / 60mn Chinese = less reliance coal, construction jobs, boat navigation better (bring vessels inland to Chongqing), tourist attraction (tertiary jobs)
- Disadvantages: towns flooded upstream (Wanxian pop. 140,000), drowned 4 cities, 8 towns, 356 villages + sacred temples, ecosystems disrupted, 1.3mn + relocated, resettlement land 800m+ asl = farming lack, 156,000 acres flooded, downstream deprived fertile sediment (30-60% sediment trapped behind dam), pressure held back water = earthquakes (engineered to withstand 7.0), 86% decrease primary productivity, waste not washed away = pollution, expensive $10.4bn build, chinese river dolphin endangered, 32 generates $5mn each,
9
Q
Dam 2
A
Aswan Dam, River Nile, Egypt
- Advantages: flood/drought control (allow crops in dry yrs e.g. 72/3), irrigation (60% water from dam for this - 4,000km desert irrigated), HEP (7,000mn KW hours yr), improved navigation, recreation/tourism, $500mn yr to Egyptian economy
- Disadvantages: dam provide less than half water expected, crop yields reduced on 1/3 area irrigated by dam (salinisation), seepage = increased groundwater levels = secondary salinisation, up to 100,000 Nubian ppl removed from ancestral homes, archaeological sites (Rameses II / Nefertari) moved to safe locations as drowned (now impact by weathering), earthquake 1981 thought caused by dam, infilling 100mn tonnes yr, erosion lowering channel 25mm 18yrs, 2.5cm erosion yr Nile delta, $100mn buy fertilisers yr to make up for nutrient loss, sardine yields down 95%, 3,000 jobs fisheries lost, stagnant water = disease e.g. bilharzia
10
Q
Artesian Basin Example
A
- Great Artesian Basin, Australia
11
Q
(Groundwater Management) Subsidence
A
- Mexico City sunk 8m+
- London 8cm 1865-1931 (over-use)
12
Q
(Groundwater Management) Country / Basin
A
UK / Thames Basin
- London Basin artificial abstraction
- Chalk aquifer SE England up to 200km3 water - London GW up to 18,000yrs old
- post-industrial city - when industrial subsidence and saline intrusion (London water table decreased 30m+), now closed heavy industry = water table rise 2m year
- London 46% reduction GW abstraction = water table risen 20m = increase flows, flooding, pollution, swell clays, foundations concern
- Hundreds boreholes/springs Thames Basin daily use (GW abstraction = 2,305mn+ litres day)
- 300+ public supply sources from GW
- 2/3 catchment permeable = direct recharge from rainfall - potential pollution infiltrate
- rainfall 850-650mm year; recharge 124-524mm
- River flows depleted, saline intrusion, rising nitrate concentrations, chemical pollution
13
Q
Salt- Water Intrusion 1
A
Manila, Philippines
- GW use = water table falling 50-80m
- water heavy concentrations salt and minerals from surrounding rocks
- water must be pumped as fallen below piezometric surface
- salt water into Guadalupe aquifer - reached 5km inland
14
Q
Pollution 1
A
Merida, Mexico
- pop 535,000
- water supply 240mn litres day all from limestone aquifer
- no sewage system / storm water drainage
- high water consumption per head = 460 litres day (greater than urban recharge 600mn annum)
- shallow aquifer contaminated
15
Q
Salt- Water Intrusion 2
A
Maldives
- huge problem small ocean islands
- GW only source freshwater
