Hee! A little bit of xkcd geog before the actual LORMS(:
RIVER MANAGEMENTRiverine Floods – overflowing of water from the banks of the river onto the floodplain when carrying capacity of river has exceeded
River Management – control of flow in river; reduces floods
Re-alignment/Channel Straightening removes meanders, reduces length of river to increase speed of river and wash away sediments that have accumulated on riverbed, minimizing localised flooding. High river discharge channelled away from flood-prone area but delivered faster downstream where floods may occur. Greater river energy, more erosion, river channel deepened, greater capacity, keeps floodwaters in, reducing flood occurrence. Wetlands may dry up & shrink; river no longer flows there.
Waikanae River, New Zealand. Effective in reducing occurrence of floods, reduce loss of property such as farmland and residential land, financial losses, loss of lives.
Very costly, 1.1million New Zealand Dollars spent. Hence it may not be practical for large rivers, LDCs.
Re-sectioning/Channel Widening as rivers are widened, deepened (dredging) to contain excess water, preventing floods. River bed and banks smoothened with cement, granite; reducing friction with wetted perimeter and increasing river speed so floodwaters flow away more quickly.
Singapore River along Boat Quay to prevent flooding in CBD as this may disrupt transport, businesses; strengthening of bank will also allow usage of area next to the river for F&B outlets for tourists.
Effective in short term, but new sediments deposited requires regular removal – costly maintenance.
Raising and Strengthening of River Banks by walls of earth, rock or concrete (called dykes or embankments) being built, confining water to channels, increasing river capacity – able to hold extra water during times of high discharge – can be very effective for preventing floods.
May make floods worse if river overflows artificial higher banks with constant deposition on riverbed, making it more shallow and raising riverbed above floodplain. Floods are also sudden; harder to flee surging floodwaters. Possibility of dyke collapse if materials used are not concrete/hardy. High cost of building dykes. Built on upper stretches of rivers in Bangladesh, floods still occur at delta.
Increased time of flooding as embankments prevents backflow into river; thus areas of stagnant water are created, increasing the likelihood of diseases (cholera and malaria). Embankments may cause some wetlands to dry out leading to a loss of biodiversity.
Mississippi River, USA – reduced frequency of floods, not completely effective. 1993 major floods, by record spring rains, flooding about 8 mil acres by early August. Raging floodwaters inflicted major damage on levees, dams & floodways, ruining 12mil acres of cropland, causing over $10 billion in damage.
Huang He, China – higher dykes constantly built and supplemented in modern times by reforestation and storage reservoirs. In 1887, Huang He broke through levees killing over 1 million people.
Planting of Vegetation along the river to protect the riverbanks from erosion as roots hold onto the soil so that less sediment is transported, deposited in the riverbed reducing silting of channel. Presence of vegetation intercepts precipitation, slows down runoff, volume in river does not rise quickly to avoid floods. Increased shade from trees on riverbank may affect aquatic plants, food chains. In Ohio, US.
Salmon River, Langley, British Columbia, Canada has planting of vegetation by Trinity Western University staff and students, members of Langley Environmental Partners Society & Volunteers.
Construction of overflow/ diversion channel has the channel split into 2, allowing some water to take a quick route across the meander/former channel, at no cost – doubles water capacity but delivers water faster downstream causing problems there.
Sluice gate – controls flow of water, only measure which is adjustable and can be useful to respond to flow conditions, used in conjunction with overflow channel.
Creating floodways by designating an area along the river where no construction is allowed, a nature park where river can flood naturally. Some cities cannot afford to leave any land unused.
Constructing dams as excess water brought by heavy rain is stored in reservoirs behind dams, reducing occurrence of floods downstream. Allows flow of water to be controlled, generates HEP, but expensive, limited lifespan as accumulation of sediments behind dam raise reservoir bed. Large-scale and causes land upstream to be permanently lost. Three Gorges Dam, China; Tucurui Dam.
Tackling the causes of floods; Controlling Land Use by using land in drainage basin properly –
MOST EFFECTIVE METHOD. Proper control of lumbering, agriculture and development in a drainage basin helps to minimize rapid surface runoff into rivers,
Reduce deforestation and have afforestation RFD (replant trees on bare slopes), reducing flow into river, lengthening lag-time but other land use could be more profitable.
Educate farmers on good farming techniques; contour ploughing, cutting terrace in slopes – reduce soil erosion.
Ensure construction associated with development will not silt up rivers
Reducing consequence of floods by flood proofing properties, flood resistant structures to reduce damage, flood-warning scheme (monitoring weather patterns, issue warnings using mass media), evacuation procedures, flood insurance to recoup losses suffered, post flood management measures – shelter, food, water.
Labels: Geography
