This document discusses key concepts related to floods and floodplains. It defines key terms like basin, divides, tributaries, and discusses the relationship between stream size and abundance. It explains how land surface shape reflects the erosive effects of moving water. It also summarizes factors that influence a stream's gradient, channel characteristics, and sediment transport capabilities. Finally, it briefly discusses the impacts of floods and some strategies to mitigate flooding risks.

1. New vocab: “polar vortex”
Feature of [usually] polar
climate where strong winds
circulate and make a very
cold air mass
Held together by jet sream
The idea is that this feature
is actually weaker, now
shifting and moving south
[that is over us]

2. The flood threat comes as
Congress is to consider whether
to help fund a nearly $2 billion
diversion channel around the
Fargo-Moorhead area, a project
that has come up against
roadblocks.
Fargo-Moorhead residents battled three straight major floods beginning in
2009, when the record crest forced thousands to evacuate and caused an
estimated $100 million in damage.
Fargo has spent $100 million on flood protection since the 2009 flood, buying out
hundreds of homes in low-lying areas and building about 20 levees. Moorhead has
invested more than $88 million on similar projects in the last four years.

3. Water cycle
Stream characteristics
Sediments
Floods
Floodplains

4. Lots of freshwater in
hydrosphere, but not much in
circulation
Huge amounts of water in
oceans, glaciers
Loads of water moves slowly
through groundwater and stays
in storage for up to millions of
years
Notice all the water goes down 
except of course for the vapor

5. Basin = entire drainage bowl
Edges of basins are marked by
divides where water flows in different
directions
Network has many levels of feeder
streams = tributaries
divide
Very consistent relationship between
stream size and abundance – many
more small streams than big ones –
pattern is the same everywhere
tributaries

6. Land surface shape reflects moving water = erosion +
underlying soil/geology
In this map, streams are shown in V shapes and linear valley features

7. Why do streams look and act
the way they do?

8. Stream profiles start steep and end shallow – this
drop or slope of stream is called its gradient
More feet drop per mile = more energy
Coast – 2‟/mile
mountain – 200‟/mile
Up  downstream
Overall course is also different
Up  downstream

9. Rocky, multi
ple channels
Two classic types –
braided and meandering
Downstream parts often
have more meanders
floodplains
deltas

10. Transport energy is
related to the
discharge and area
across the
stream, and so
gradient matters
also
Higer
discharge, higher
competency

11. Coarse  fine
Size, amount and transport distance is directly linked to energy
Bedload >>
suspended load

12. Dynamic interplay of
erosion and deposition
Rivers erode and migrate over time, developing stream sinuosity

13. Simply, discharge > channel
Above bankfull stage, water spills out
past levees into floodplain
Floods carry sediment, organic
debris, and energy outward
Energy  sediment load, so finer sediments travel farther and longer

14. Northern &
Central, Spring
2010
Southern & Central,
9/24-26 2010
Minnesota & Mississippi Rivers +
tributaries [Zumbro, Cannon, etc]
Southern & Central, 2011?
63% chance „major‟ St Paul
flooding

15. Frequency and
especially
recurrence –
episodes or
trends?
The “100-year flood”
Our forecasts
depend on pas
measurements

16. Floods affect large
areas of inhabited land
Direct effects
-drowning
-sedimentation
Indirect effects – long term devastation is
much more important in economic and
human terms
…such as?
What are the human / biotic impacts?

17. So… what do we do?
De-urbanize / preserve
channels and floodplains
Increase wetlands / recharge
Sandbags? Levees?
Zoning? Forecasting?