Class Notes (839,194)
Canada (511,223)
Geophysics (26)
GOPH 375 (26)
All (17)

Chapter 13.docx

3 Pages

Course Code
GOPH 375

This preview shows page 1. Sign up to view the full 3 pages of the document.
Chapter 13: Floods  Big floods are rarer than little floods  Hydrograph: discharge vs. time  Base flow is the part of the river that flows all the time o Ground water flows in winter  Stream floors have a steeper bottom/slope (higher gradient) near the stream source, and a flatter bottom (lower gradient) near the stream mouth  Base level - level below which a stream cannot erode  Discharge – the rate of water flow expressed as volume per unit of time  Load – available sediment amount waiting to be moved  Gradient – the slope of the stream bottom  Channel pattern – the sinuosity (curves) of the stream path  Graded stream theory: Streams maintain equilibrium by changing the gradient of the sea bottom o Too much discharge: rapid water flow erodes the stream bottom and increases the load, reduces the vertical drop, and creates more curves to use up extra water energy o Too much load: built up sediment on the stream bottom increases the gradient, thus the water flow, stream becomes straighter (braided stream?) o Lakes are temporary features streams are trying to eliminate o Typical stream has a braided stream upstream (too much load), and meanders downstream (too much discharge)  Rainfall infiltration into ground is most common in porous/dry soil that’s flat with vegetation. Runoff occurs on already saturated ground with steep slopes  Flood plains: floors of streams during floods; are at a high risk of flooding again. Short streams have a higher chance of flooding.  Flow duration curve plots discharge (vertical axis) vs. accumulated frequency % (horizontal) o Curve is not connected to vertical axis because you can’t ever say the river will never get higher than a particular point – can’t ever find top height o Flood frequency curve – historical floods plotted; the larger then flood, the rarer it is. Curve should influence building construction.  Recurrence interval how often, on average, a flood will reach a certain discharge o Calculated by T= (N+1)/m  T = answer is in years, how often that discharge level will occur  N = number of years of record  M = magnitude (rank in series from largest to smallest) o 100 year flood (recurrence interval of1qaz 100) means there’s a 1% chance of that discharge level happening each year o Cumulative probability – the longer the wait, the more likely a flood will occur; but the probability of flood each year is the same regardless of when the last flood occurred  Red River Floodway: in Manitoba, regular flooding because it’s relatively young so it hasn’t created a deep valley yet, the clay underlying the river impedes infiltration into the ground, the lake is shallow, melting winter snow o 1950 blizzard (winds + precipitation) combined with melting snow caused dikes protecting Winnipeg to collapse, mass evacuation o Floodway built in response to flood, trench diverting excess water o 1997 floods caused by larger than average drainage basin and melting of frozen water saturated in the soil. Floods caused fires, floodway protected Winnipeg Flood Styles:  Hydrometeorlogical floods occur in relation to specific weather conditions (thunderstorm, cyclone, snow melt). Most floods are most common in Canada o Rainfall floods: when precipitation rate exceeds infiltration capacity water becomes runoff. Flash floods. Meter deep water can wash away cars. Common in the Amazon/Brazil and other tropical areas  1972 Rapid Creek Flood, North Dakota. Dam collapsed, 238 people died.  1996 Sague
More Less
Unlock Document

Only page 1 are available for preview. Some parts have been intentionally blurred.

Unlock Document
You're Reading a Preview

Unlock to view full version

Unlock Document

Log In


Join OneClass

Access over 10 million pages of study
documents for 1.3 million courses.

Sign up

Join to view


By registering, I agree to the Terms and Privacy Policies
Already have an account?
Just a few more details

So we can recommend you notes for your school.

Reset Password

Please enter below the email address you registered with and we will send you a link to reset your password.

Add your courses

Get notes from the top students in your class.