Geological Hazards and Their Impact_McGeary_Date_042810

Geological Hazards and Their Impact_McGeary_Date_042810 - n...

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Intensity of Flooding - how quickly water rises - max discharge Overall Intensity - climate (rainfall, previous rainfall, freeze-thaw) - geology - development - geography (location within drainage basin) Flash Floods very rapid runoff and flooding - thin soils (Texas, CA, Arizona) - flat topography (rain on frozen ground, N. Dakota) snow melts in US, still frozen in Canada stream runs north into Canada Recurrence Interval Floods - 100 year flood odds are 1/100 in any given year (1% or 0.01) - 100 year floodplain area inundated by 100 year flood How to Determine? 1) for every year, take the biggest discharge, for as many years as possible 2) rank them from largest (rank 1) to the smallest (if 50 years, rank 50) 3) R.I. = (n+1)/M
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Unformatted text preview: n = number of years m = rank number i.e.: if you had 99 years worth biggest R.I. = (99+1)/1 = 100 second biggest = (99+1)/2 = 50 smallest = (99+1)/99 = about 1 Can plot discharge versus R.I. on special graph paper Good R.I. analysis requires:- at least 30 years of observation- no major changes to the factors that control flooding over time • no climate change • no land use changes o urbanization o deforestation o engineer dams and levees ← ← ←- Red clay creek, Delaware, Oct. 2 2003 Mitigation Option 1) reduce volume of water supplied from upstream • build a dam • vegetation ← 2) “contain or reduce water levels • levees • bypass channels ← 3) flood insurance ← 4) abandon flood plain and let river flood ←...
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