Rivers

Front 1

Rivers: Historical Use

Back 1

1. Farming- Alluvium (stream-deposited soil)

2. Water Supply

3. Waste Disposal

4. Commerce

5. Floodplain
flat surface adjacent to the river channel that is periodically inundated by floodwater (a larger valley of the river)

6. People have always modifies the land, altering the drainage basin

Front 2

Streams and Rivers

Back 2

1. Streams and rivers are part of the water cycle

2. Runoff


3. Drainage Basin

4. Drainage Divide

5. Slope

6. Base Level

7. Local base level

8. Ultimate Base Level


9. If a stream is above base level, it will downcut

10. If a river is below base level, it will build up (dam/reservoir)

Front 3

Runoff

Back 3

1. Overland Flow
Sheet Wash
an even flow across a relatively flat surface

Rill Wash
water that moves through small linear depressions

2. Channelized Flow
Brook/Branch
small channels

Creek

Stream

River

Front 4

Drainage Basin

Back 4

1. the land area that contributes water to a point on a stream

Front 5

Drainage Divide

Back 5

1. highland area that separates adjacent drainage basins

Front 6

Slope

Back 6

1. Typically Higher in the headwaters and lower at the mouth

Front 7

Base Level

Back 7

1. Level to which a river may down cut

Front 8

Local base level

Back 8

1. realistic level below which a river will not downcut

Front 9

Ultimate Base Level

Back 9

1. sea level

Front 10

Sediment in Rivers- Competency

Back 10

1. Largest size of particle that can be transported as bed load (biggest thing that can be scooted along the bottom)

Front 11

Sediment in Rivers- Capacity

Back 11

1. Measure of the total load that a stream can carry

Front 12

Sediment in Rivers- Stream Load

Back 12

1. Base Load
Materials transported at the bottom of the stream by rolling, sliding and saltation

2. Suspended Load
Material being carried with the water above the stream bed

3. Dissolved Load
Dissociated ions usually produced by chemical weathering

Front 13

River Velocity

Back 13

1. The volume of water moving by a particular location in a river per unit time

Front 14

Channel Patterns- Meandering

Back 14

1. Flow over a usually gentle surface (with the exception of the Grand Canyon)

2. Stream lengthens by cutting laterally

3. Grand Canyon- Incised into the underlying topography below uplift

Front 15

Discharge

Back 15

1. Q (Discharge) = W (width of flow) * D (depth of flow) * V (velocity)

2. W * D = Cross sectional area flow

3. Bank Full Discharge

4. If the channel size is decreased, by construction of the bank of shallowing, the velocity increases

5. If the channel size is increased, by spreading out the channel or deepening, the flow will decrease

Front 16

Erosion

Back 16

1. Occurs where velocity increases and the river is above the base level

Front 17

Sediment Deposition

Back 17

1. Occurs when the velocity decreases (empties out into a larger bodies such as a lake or ocean (delta))

Front 18

rivers: Effects of Land-Use Changes

Back 18

1. Increased sediment load

2. Stream channels tend to have a slope and cross sectional shape that provides the velocity of flow necessary to do the work of moving the sediment load

3. An increase or decrease in volume of water or sediment load will change the character of the river

4. Damming a stream tends to trap sediment and starve the downstream areas

Front 19

Channel Patterns- Straight

Back 19

1. Steep slope or underlying structure

2. Generally only occurs for a short distance

Front 20

Channel Patterns- Braided

Back 20

1. Pulse flow, usually over coarser sediments

2. Flow, such as from melting ice and snow which waxes and wanes during the day/night cycle

Front 21

Channel Patterns- Meandering

Back 21

1. Flow over a usually gentle surface (with the exception of the Grand Canyon)

2. Stream lengthens by cutting laterally

3. Grand Canyon- Incised into the underlying topography below uplift

Front 22

Floodplains and Floodplain Features

Back 22

1. Larger river channel that handles the water flow when the stream leaves its primary channel

2. Pont bar
where we’re increasing the sediment load

3. Cut bank

4. Oxbow Lake

Front 23

Flooding

Back 23

1. Flooding occurs when the water flow exceeds the capacity of the primary channel

2. The water backs up, and eventually leave the primary channel into the secondary or higher channel

3. Flood discharge

Front 24

Upstream Flood

Back 24

1. Occur in the upper parts of drainage basins and are generally produced by intense rainfall of short duration over a relatively small area.

2. Usually brief

Front 25

Downstream Flood

Back 25

1. Occur in the lower parts of the drainage basin and are produced by long rains over a broad area

2. Cover wide areas

3. 1993 Mississippi River Flood

Front 26

Urbanization and Flooding

Back 26

1. Urbanization has increased the frequency and magnitude of flooding

2. The rate of increase is a function of the percentage of the land that is covered by impermeable surfaces (roofs, pavement and cement)

3. Impervious cover and storm sewers are measures of urbanization

4. An area with 40% impervious cover should expect to have about three times as many floods

5. Floods are a function of rainfall-runoff relationships

6. Built-up debris, bridges that trap debris, and other things can back up water and contribute to flooding

Front 27

Factors that Cause Flood Damage

Back 27

1. Land use on the floodplain

2. Magnitude, or the depth a velocity of the water and frequency of flooding

3. Season; for example, growing season on the floodplain

4. Sediment load deposited

5. Effectiveness of forecasting, warming, and emergency system

Front 28

Effects of Flooding

Back 28

1. Primary- directly caused by the flood

•Injury
•Loss of life
•Damage caused by swift currents, debris, and sediment to farms, ,homes, buildings, railroads, bridges, roads and other communication systems
•Erosion and deposition

2. Secondary- caused by disruption and malfunction of services and systems due to the flood

•May include short-term pollution of rivers, hunger and disease, and displacement of people who have lost their homes
•Fires from short circuits

Front 29

Adjustments to Flood Hazards- The Structural Approach - Physical Barriers

Back 29

1. Levees (earth), floodwalls (concrete) and reservoirs (on-site retention basins)

2. Some of these structures make flooding worse, if they fail. Such as in North Dakota and New Orleans

Front 30

Adjustments to Flood Hazards- The Structural Approach -Channelization

Back 30

1. Strengthening, deepening, widening, clearing, or lining existing stream channels are methods of channelization

2. Engineering technique with the objective of controlling floods, draining wetlands, controlling erosion, and improving navigation

Front 31

Opposition to channelization is based upon

Back 31

1. Drainage of wetlands adversely affect plants and animals by eliminating habitats necessary for the survival of certain species

2. Cutting trees along the stream eliminates shaping and cover for fish and exposes the stream to the sun, the exposures results in damage to plant like and heat sensitive organisms

3. Cutting hardwood trees on the floodplain eliminates the habitats of many animals and birds, while facilitating erosion ands situation of the stream

4. Straightening and modifying the streambed destroy both the diversity of flow patterns and the feeding and breeding are for aquatic life while changing peak flow.

5. Conversion of wetlands from a meandering stream to a straight, open ditch seriously degrades the aesthetic value of a natural area

Front 32

Adjustments to Flood Hazards- Channel Restoration: Alternative to Channelization

Back 32

1. Uses various techniques: cleaning urban waste from the channel, allowing th stream to flow freely, protecting the existing channel banks by not removing existing trees or, where necessary, planting additional trees and other vegetation

2. Buffalo Bayou West Sector

Front 33

Adjustments to Flood Hazards- The Structural Approach-Channelization

Back 33

1. Not all channelization causes degradation, but artificial systems can only serve people, not the plants and animals of the original ecosystems. Sometimes writers of the textbook cant see beyond their anthropogenic view

Front 34

Adjustments to Flood Hazards- Flood Insurance

Back 34

1. The federal government through the U.D. National Flood Insurance Program, makes flood insurance available at subsidized rates for people in Special Flood Hazard areas

2. If you buy or construct a home within the 100-year flood plain (as identifies by FEMA flooding maps), you must purchase flood insurance to get a loan

3. Tropical Storm Allison Project FEMA map server for Harris County

4. The flood rate maps must be updated every five to ten years to account for the additional volume of water because of decreased infiltration

Front 35

Adjustments to Flood Hazards- Flood-proofing

Back 35

A. Methods
1. Raising the foundation of a building above the fold hazard level by using piles or columns or by extending foundation walls or earth fill

2. Constructing floodwalls or earth beams around building to seal them from floodwaters

3. Using waterproofing construction such as waterproofed doors and waterproofed basement walls and windows

4. Installing improved drains with pumps o keep flood waters out

B. Buildings can also be modified to reduce flooding problems

Front 36

Adjustments to Flood Hazards- Floodplain regulation

Back 36

1. Environmentally, the best approach to minimizing flood damage in urban areas is floodplain regulation
2. A compromise between unregulated use and no use whatsoever

3. The floodplain belongs to the river system, not to people

4. In some cases, frequent flooding requires the tearing down of structures and refusal of insurances

Front 37

Adjustments to Flood Hazards- Flood Hazard Mapping

Back 37

1. Construction of the maps includes looking at past evidence of flooding, historical records, geological analysis, and elevation maps

2. The floodway is the first secondary channel above bank full discharge

3. Zoning for land use

Front 38

o Relocating People from Floodplains: Examples from North Carolina and North Dakota

Back 38

1. North Carolina
•September 1999, Hurricane Floyd (20 inches of rain)

•$50 million was spent to remove 430 homes of (700 homes) that were damages

•Largest single-home by-out by government

2. North Dakota

•Churches Ferry, North Dakota

•Flat northern plains

•The lake on the plains were flooding out from their banks, and encroaching on the city

•A city of 100 people has shrunk to 7 after most were bought out by the government

Front 39

Preparing for a flood: What to Do

Back 39

1. Check the flood rate maps for frequency of flooding

2. Purchase flood insurance

3. Buy sandbags of flood boards to block doors

3. Make a flood kit

4. Fins out where to cut services that may cause fires

5. Talk and make a plain in case flooding occurs

Front 40

Preparing for a flood- Not to Do

Back 40

1. Underestimate the threat, or decide you can control it

Front 41

When you learn a flood warning has been issued- Do

Back 41

1. Be ready to leave

2. Observe water levels and check the radio and TV

3. Move people and animals into upstairs rooms

4. Move cars to higher ground

5. Check on neighbors

6. Do as much as you can do during daylight

7. Keep warm and dry

Front 42

When you learn a flood warning has been issued- Not to Do

Back 42

1. Walk in floodwaters

Front 43

After a flood- Do

Back 43

1. Check the house and document damage

2. File a claim, if you have insurance

3. Remove damage carpets and furniture, dry to avoid mold

4. Contact utility companies to see if its okay to turn them back on

5. Open doors and windows and ventilate the home

6. Run water to clean pipes and fixtures

Front 44

After a flood- Not to Do

Back 44

1. Do not work with items that were in flood waters without gloves

Front 45

Perception of Flooding

Back 45

1. People are tremendously variable in their knowledge of flooding, anticipation of future flooding, and willingness to accept adjustments caused by the hazard