Lecture 13.2: Effects of Floods

Socio-economic effects: geographically uneven. e.g. in DCs, deaths declining but 3/4 of property losses from floods occur due to extensive built-up areas. in LDCs, higher death rate due to inadequate flood management systems & pop. pressure which causes ppl to settle in floodplains

Environmental

Environmental effects: more '+' than '-'

Socio-Economic

Loss of Lives

Spread of Diseases

Disruption of Svcs

Dispersal of Nutrients & Pollution

Impact on Eco-system

Socio-Economic

Damage/Loss of Property

Agriculture & Livestock

by drowning, diseases, structural damages

claim 20,000 lives worldwide annually

flood management measures can still fail in DCs e.g. 2005 Hurricane Katrina killed nearly 2000 ppl in New Orleans due to levee failure

transportation: food & cleaning supplies shortage-> starvation in LDCs.

high v of H2Os transport larger particles as suspended load. can undercut & erode foundation of buildings, bridges, levees-> collapse or need repair. displace ppl from homes.

e.g. in rural Bangladesh, houses w/ mud/tin walls in slums can collapse. 32% of pop. lives in slums so many left homeless.

when floodH2Os retreat, v much lower, deposition occurs. everything covered in mud, including building interior-> huge cost of cleaning & damages

drowning of crops, livestock & damage to infra

countries w/ large agrarian economies like Nepal affected most. e.g. in Bangladesh, agriculture forms 18.6% of GDP, employs 45% of labour force.

LT '-' impact is topsoil erosion. topsoil is where decomposition & nutrient cycling happens. erosion results in reduced productivity of land (less nutrients supplied)-> abandonment

maintains soil fertility by depositing layers of alluvium & flushing salt out of soils-> better harvests

gas & electricity: disruption of daily activities, temporary closure of factories & industries to fire & explosion

e.g. August 2014 Nepal floods: 21,000 fams affected as access to them cut off by damaged roads.

impt urban sectors like urban infra, trade etc. hampers econ productivity during & after floods

dehydration (little to no access to clean H2O) + disease epidemics

gastro-intestinal diseases break out in LDCs w/ low sanitation standards/damaged sewer systems-> drinking H2O polluted, esp. if sewerage treatment plants are flooded

e.g. Feb/Mar 2000 Mozambique floods: nearly 2000 cases of cholera, 100s of cases of malaria

infiltrating & percolating floodH2Os recharge H2O table, provides LT H2O supply to plants

maintain ecosystems by providing breeding, nesting, feeding & nursery areas for fish & shell fish

high magnitude floods can sweep plants away, drown animals-> loss in wildlife & biodiversity

deposited alluvium helps keep elevation of land mass above sea lvl. e.g. b4 dams & levees were built along Mississippi river, floods would deposit sediments on delta. w/o continued replenishment, delta is subsiding @ abt 100km2 yearly

cause pollution esp. in urban areas. disrupt normal drainage systems, overwhelm sewer systems-> raw/partially raw sewage spills.

destruction of buildings that contain toxic materials (pesticides, gasoline etc.) can cause release of these materials