Engineered approaches to hazard mitigation

Hard engineering

Utilizes rigid, man-made structures to control natural processes (involves steel, concrete, and other hard materials

Soft engineering

Works with natural systems to provide sustainable, adaptable solutions

Example of hard engineering with rivers

Channelization (channel enlargement, embankments, straightening, creation of new channels)

Nine principal types of channelization

Resectioning, realignment, diversions, embankments, bank protection, lined channels, culverts, detention dams, maintenance

Resectioning

Increase width/depth, increase cross sectional area, increase channel capacity

Realignment

Straightening channel by making cuts, increase gradient, leads to velocity decrease in flood levels

Diversions

Alteration of natural course

Embankments

Dikes, bunds, levees, stop banks (banks bult adjacent to the channel to confine floodwaters

Bank protection

Designed to slow or halt bank erosion, groynes, training fences, revetments, gabions, rip rap, fascines

Lined channels

Usually involves concrete, expensive so only seen in urban areas

Culverts

construction of underground channels

Detention dams

Built to decrease flood peaks and/or trap sediment

Maintenence

dredging, cutting and removal of vegetation, removal of rock obstacles

Consequences of channelization

Disturbance of natural hydrological and sediment transport conditions, increased bed gradient, increased sediment transport capacity, bed erosion

Options for soft engineering

Land use management, wetland and riverbank conservation, river restoration, warning, preparation

Examples of soft engineering structures

Cross-vanes, imbricated rip rap, boulder step pools, brush layering, engineered log jams

Cross-vanes

U shaped structures of boulders or logs, built across the channel to reduce velocity and energy near the stream bank

Imbricated rip rap

Stones are placed along the stream bank in an overlapping pattern to protect the bank from erosion

Boulder step pools

Pools built from boulders, emulating natural features velocity, habitat variation

Brush layering

Live branch cuttings are places along the stream bank. As new plants sprout from the live branches, the roots anchor the soil and prevent erosion

Engineered log jams

Built log jams — emulating natural features

Advantages of soft engineering

cheaper to maintain, flooding becomes more predictable, recreational opportunities, aesthetics, improved ecosystem services

disadvantages of soft engineering

Not all land may be well protected, compromises in flood protection level

What are hazards associated with earthquakes

ground failure, structural failure

Two approaches to mitigating earthquake damage

improve ground conditions and improve design of structures

Densification

increasing the compaction and friction of soil to prevent liquefaction from earthquakes

Vibroflot

Water and mechanical vibrations to increase density and strength up to 50 m

highest winds of hurricane Katrina

280 km/h

what failed making hurricane Katrina such a bad disaster

levees and flood walls failed and were breached in more than 50 locations

How much of New Orleans was flooded by hurricane Katrina

80%

Roughly how many people died in hurricane Katrina

1,118 death and 135 missing

How many people fled the city during hurricane Katrina

400,000