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Impact of Urbanization on Flooding
Published in Saeid Eslamian, Faezeh Eslamian, Flood Handbook, 2022
In the practice of floodplain management, the 100-year or 500-year floods in the USA are defined as a particular design flood (FEMA, 1985). As shown in Figure 5.6, a 100-year floodplain defined by FEMA means that area that would be inundated by the 100-year flood (FEMA, 1985), which is frequently divided into the floodway and the flood fringe. The floodway is an area near the river or stream that experiences regular flooding and large enough velocities to cause damage, which contains the 100-year peak flow with not more than a one-foot increase in depth above that which would occur if the entire cross-section carried the 100-year peak flow (FEMA, 1985). No homes or structures should be built within the floodway. The flood fringe is the peripheral area between 100-year floodplain and floodway, which is inundated during flooding but experiences only small velocities. In order for a flood-prone property to qualify for NFIP, a local community must adopt an ordinance that protects the floodway and requires that new residential structures built in the flood fringe be elevated to at least the level of the 100-year flood, while commercial structures can be elevated or floodproofed to or above this level (FEMA, 1985).
Urban stormwater planning
Published in James C. Y. Guo, Urban Flood Mitigation and Stormwater Management, 2017
Land development projects tend to achieve high density in land uses utilizing the most economic measures. Thus, floodplains become valuable if the low land areas can be reclaimed for development. The purpose of floodplain management is to provide guidance, conditions, and restrictions for development in floodplain areas while protecting the public’s health, safety, welfare, and property from danger and damage. To provide impetus for proper floodplain management, the US government, acting through the Federal Emergency Management Agency’s National Flood Insurance Program (FEMA NFIP), has established regulations for development in floodplain areas. Compliance with these regulations allows property owners to obtain lower cost flood insurance premiums and/or eliminates the requirement for the owner to obtain flood insurance as a condition for obtaining government-supported loans. FEMA has adopted the 100-year flood (1% chance of annual occurrence) as the base flood for floodplain management purposes and delineates the 100-year floodplain on their maps. For certain stream courses studied by FEMA by detailed methods, a floodway may also be depicted. The floodway is a portion of the floodplain and is defined as the channel itself plus any adjacent land areas that must be kept free from encroachment in order to pass the base flood without increasing water surface elevations by more than a designated height such as 1 ft in rural areas or 6 in. in urban areas.
Markov-based deterioration prediction and asset management of floodway structures
Published in Sustainable and Resilient Infrastructure, 2022
Huu Tran, Weena Lokuge, Warna Karunasena, Sujeeva Setunge
In Australia, floodway structure is a small road section apart from bridges and culverts, that is designed to carry road traffic with underneath drainage pipes in some cases and is also designed to be overtopped to allow flood crossing during flood events. Figure 1 shows an example of type 4 floodway structure used in the Lockyer Valley Region of Queensland in Australia, which often have a road surface with road substructure, a reinforced concrete slab with apron and cut-off wall, rock protection against scouring and drainage pipes or culverts. There are several design types of floodway structures, which differ by various arrangements of rock protection, apron and cutoff wall at upstream and downstream (floodways of Main Roads Western Australia).