chap 10 stream erosion and river systems

Describe three examples of features that serve as the local base level for a stream.

1. river 2. lake 3. reservoir formed by a human made man

Describe the fluvial conditions that lead to stream aggradation.

aggradation happens when the bed load and suspended load exceed a stream's capacity and sediment accumulates and the stream channel builds up through deposition

Where are the headwaters located within a drainage basin?

all streams start small in the uppermost in the uppermost portions of their drainage basins known as the headwaters

Identify the primary differences between an alluvial fan and a river delta.

alluvial fan: occur when flowing water abruptly loses velocity as it leaves the constricted channel at the canyon mouth. river delta: occur where a river's velocity rapidly decreases as it enters a larger, standing body of water and the sediment load is deposited

Describe the landforms created by alluvial deposition.

alluvial fans, form at the mouth of a canyon where an ephemeral stream channel exits into a wider valley. and river deltas

Describe the fluvial conditions that produce braided stream channels.

an abundant supply of sediment. high stream gradient. rapid and frequent variations in water discharge erodible banks a steep channel gradient

Explain why the country of Bangladesh is so susceptible to devastating floods.

because of the terrain, the permeability of the soil, and the monsoonal rains

Why are urban areas so susceptible to large flood events?

because they do not have natural ways of draining out water

Explain why turbulent streamflow is more common than laminar streamflow in mountain environments.

because turbulent streamflow occurs in shallow, steep headwater streams and in sections with rapids on all streams. turbulent movement results from friction between streamflow, the channel sides and bed, and obstacles such as boulders in the channel

Describe why, throughout history, flood- plain environments have attracted human settlement.

becuase these areas offer good soil, moderate temperatures, etc

Identify three factors that influence stream discharge.

channel width, channel depth, and stream velocity

Describe the difference between stream competence and stream capacity.

competence: a streams ability to move particles of a specific size, is a function of stream velocity and the energy available to move materials. capacity: the total possible sediment load that a stream can transport

Define drainage density.

determined by dividing the total length of all stream channels in the basin by area of the basin. the number and length of streams in a given area reflect the area's geology, topography, and climate. high drainage denstities develop in areas where precipitation cannot infiltrate into the soil, and instead flows overland to form a dense network of stream channels.

Describe the sequence of events that creates a floodplain.

erosion, flooding, deposition left behind by floods, agricultural development

Explain what is meant by a 200-year flood rating.

floods are rated statistically for the probablity that a flood will occur sometime during a given time interval, based on historical data. IE 10-year flood has a 10% likelihood of occurring in any one year and is likely to occur 10 times each centuray, which is a pretty moderate threat

Explain how alluvial stream terraces are formed.

forces other than flowing water can reshape the alluvial deposits on the floodplain. tectonic uplift or a lowering of base level rejuvinates stream energy so that a stream again scours downward. the resulting entrenchment of the river into its own floodplain produces alluvial stream terraces on both sides of the valley

Describe how you would go about calculating the stream discharge of a river near your home.

getting down and dirty and going to the stream itself

Identify the main cause of the 2010 floods that inundated Pakistan's Indus River plain.

heavy monsoonal rains swelled the indus and caused the flooding

List the reasons why river deltas are often favored for human settlement.

humans settle deltas for their level terrain, proximity to water, and fertile soils

Describe two processes by which streams carry out erosion.

hydraulic action: the squeeze and release action of flowing water that loosens and lifts rocks turbulence: turbulent flow increases erosion by hydraulic action.

Explain the difference between an interfluve and drainage divide.

interfluve: an area of high ground that separates two river valleys

Explain the significance of a continental divide.

on every continent these divides provide a spatial framework for water-management planners who must balance the competing demands of urban, agricultural, and industrial water users.

Explain the difference between a perennial and ephemeral stream.

perennial: flow all year, which is typical for large rivers and in humid regions with ample ample precipitation ephermeral: flow only after precipitation and are not connected to groundwater systems

Use a pen or pencil to draw radial, dendritic, and rectangular drainage patterns, and indicate where you might find them.

radial: circular patterns, results when streams flow off a central peak or dome, such as occurs on a volcanic mountain dendritic: looks like tree leaves, develop on a land surface where the rocks are of uniform resistance to erosion. rectangular: look like rectangles, formed by a faulted and jointed landscape, which directs stream courses in patterns of right angle turns

Explain what the terms river and stream mean when applied to fluvial systems.

river: applied to a main stream stream: more general term now necessarily related to size

Identify the possible causes of a stream nickpoint.

stream nickpoints occur when longitudinal profile of a stream experiences and abrubt change in gradient such as a waterfall or rapids area. can result when a stream flows across a zone of hard, resistant rock or from various tectonic uplift episodes such as along a fault line. temporary blockages in a channel caused by a landslide or a logiam.

Explain the characteristics that make drainage patterns distinct from one another.

the characteristics that make drainage patterns distinct from one another are its drainage density and its individual pattern.

Predict the soil and bedrock characteristics of a watershed with a low drainage density.

the characteristics would be an area with with high vegetation, and surface bedrock that is permeable to water. the soil would be wet and there is less erosion

Explain why the Danube River is so important to humans.

the danube river important for commercial transport, municipal water, agricultural irrigation, fishing, and hydroelectric power.

Explain how the hydraulic action of a waterfall eventually works to reduce the actual height of the free-falling water.

the free-falling water moves at a high velocity under the accelaration of gravity, causing increased abrasion and hydraulic action in the channel below. this action undercuts the water. eventually, the excavation causes the rock ledge at the lip of the fall to collapse, shifting the waterfall a bit farther upstream.

Imagine that you are a drop of water in a stream. Describe how your path and velocity would change as you flow down a meandering stream.

the maximum flow velocity shifts from the center along a straight stretch of the stream channel to the outside bend of a meander. lower stream velocity on the inside of the bend.

Explain why the ocean is considered the lowest practical base level for virtually all streams.

the ocean is the lowest practical base level for virtually all streams because all streams are technically able to reach sea level

Explain why the Colorado and Nile Rivers are considered exotic streams.

they are considered exotic because some river systems that begin in moist regions flow downstream into arid landscapes where high POTET and withdrawals for agriculture and settlements may reduce the discharge, this stream is an exotic stream of distant origin

Identify what a trellis drainage pattern reveals about the underlying topography.

trellis pattern develop in dipping or folded topography that varies in resistance to erosion. indicates great anticlines and synclines of mountains.

Explain the difference between a point bar and an undercut bank.

undercut bank: the outer portion of each meander recieves the fastest water velocity, and therefore the greatest scouring action. this outer curve can be the site of a steep undercut bank. point bar: the inner portion of a meander experiences the slowest water velocity receiving deposition

Identify the difference between an ungraded and graded stream.

ungraded: actively eroding or depositing material in its channel so that its gradient is adjusted to carry the sediment load. graded: has just enough energy to transport its sediment load.

Explain why stream velocity decreases closer to the sides and bottom of the stream channel

velocities decrease closer to the sides and bottom of the channel because of the frictional drag on the water flow

Describe the movement of water and the features involved in stream formation.

water moves downslope as sheetflow, interfluves direct sheetflow into small grooves called rills that develop into deeper gullies and then into a stream. where 2 tributary streams join is called a confluence.