Flooding and Flood Mitigation

Possible essays: Hydrograph characteristics and natural influences on hydrographs(geology, seasonality), flood mitigation measures, two contrasting detailed examples of flood mitigation of drainage basins

Flood Hydrograph

Flood Hydrograph

Showss river discharge, precipitation, and time

Pakistan(Case Study): Background

Indus River, June 14th-October 2022, 1/3 of the country under water, south of the country worst hit (Sindh region)

Pakistan(Case Study): Flood Impacts

Over 1700 dead, over 17,000 injured, 33 million affected

$15.2billion in damages

897,014 houses destroyed, 1.3 million damaged, 22,000 schools damaged or destroyed, 13,000km of road + 439 bridges destroyed

1.2 million livestock killed, crops destroyed

Diarrhea, cholera, dengue, malaria, skin conditions, lack of clean drinking water

Increased human trafficking(children)

Pakistan(Case Study): Physical Causes

Heat waves in May + June → 50°+

Glacial + snow melt in Himalayas

Intense monsoon rains → 3x the 30-year average, flash floods, Sindh had 784% the August average

Pakistan(Case Study): Human Causes

Deforestation → 1.9 % forested today, 33% in 1947)

Draining of floodplains and wetlands under colonialism

Irrigation canals

Poor urban planning

Illegal rock and sand mining to meet demand for construction materials

Rapid population growth → 1.9% growth rate, 3.3 TFR

Pakistan(Case Study): Mitigation Techniques(7)

Afforestation → 2018, 10 Billion Tree Tsunami Programme, Plant for Pakistan

Agricultural Methods → drip irrigation, less intensive use of the floodplains, silvopasture, recreating wetlands

Ice Stupas

IDBM → government-level plan to manage whole basin in coordinated effort

Land Use Regulations → hazard maps, control human encroachment on river corridors

River Training → sediment control dams, inserting boulders, river bank and bed protection

Long-Term Flood Forecasting

Water Stress vs Water Scarcity

When people live on less that 1700m3 per capita per year

When people live on less that 1000m3 per capita per year → starts to halt economic development and human wellbeing

In 2016 2.6 billion lived under water stress, by 2025 3.6 billion will(48% of population)

River Otter: Details

Length: 44km

Altitude drop: 275m

Discharge: 3.12m3 per second

Located in Devon, England

River Otter: Beavers

Creates miniature reservoir + wetland around dam area to prevent flooding

Fight wildfires + droughts: wetlands store water and resist fires, carbon sink

15 family groups exist in the River Otter since their reintroduction in 2015

Mississippi: Details

Length(source to mouth): 6275km

Altitude Drop(source to mouth): 450m

Discharge: 1400 million m3 per day

Suspended Sediment: 550 million metric tonnes per year

Importance of the river: The Mississippi carries 13% freight traffic in the USA and is an important agricultural area. It is the most important navigable waterway in the USA, with the total distance of navigation throughout the system extending over 24,000km. The main cargo is grains from the Midwest and petrochemicals from the Gulf of Mexico.

Mississippi: Mitigation Techniques(4)

Levees → US Army Corps of Engineers built 350 miles of levees along the Mississippi, the levee at New Orleans is 7m high, and there's a 3m levee at Lake Pontchartrain

Diversionary Spillways → Bonnet Carre Spillway from New Orleans to Lake Pontchartrain and then to the Gulf of Mexico. Aims to take water away through overflow channels to reduce discharge in main river

Dredging → Since 1930, the Army Corps of Engineers has been tasked with dredging the river to maintain a 3-4 m deep navigation channel using boats such as The Goetz Dredge

Dams and Reservoirs → 29 lock and dam structures, 3000 dams and reservoirs