River systems Main concepts Flashcards
1) What is the geologic definition of a stream?
A) A river of water that carries large volumes of water and has many tributaries
B) A stagnant body of water with little current and low oxygen content
C) A large lake system
D) A channelized body of water flowing down gradient
D) A channelized body of water flowing down gradient.
A stream is defined as any body of water that flows within a channel and moves downhill due to gravity. This definition encompasses rivers, creeks, brooks, and other smaller flowing bodies of water. Streams can vary in size and volume but are all characterized by their flow through a defined channel.
2) Streams generally receive their water from two sources. What are those two sources?
A) Lakes and meteorites
B) Meteorites and comets
C) Overland flow and groundwater
D) Groundwater and evaporation
C) Overland flow and groundwater
Streams generally receive their water from two main sources: overland flow (also called surface runoff) and groundwater. Overland flow occurs when rainwater or snowmelt flows across the land surface and enters the stream. Groundwater contributes to streams through baseflow, where water from underground aquifers seeps into the streambed.
3) How will channel velocity change along the longitudinal profile of a stream?
A) Velocity will remain constant for the entire length of the stream.
B) Velocity will start high and gradually decrease toward the mouth due to increasing discharge
downstream.
C) Velocity will start low and gradually increase toward the mouth due to increasing discharge
downstream.
C) Velocity will start low and gradually increase toward the mouth due to increasing discharge downstream.
In a typical stream, the velocity of the water tends to increase as you move downstream. This is because, as a stream flows toward its mouth, it generally collects more water from tributaries and rainfall, which increases the discharge (the volume of water flowing through the stream). With a larger discharge, the stream’s cross-sectional area typically increases as well, allowing for faster water flow. Additionally, the gradient (slope) of the stream usually decreases downstream, leading to less friction, which can also contribute to higher velocities.
) Which of the following particle sizes is most likely to make up a stream’s suspended load?
A) Gravel
B) Clay
C) Sand
D) Silt
D) Silt
The suspended load of a stream consists of fine particles that are small enough to be carried by the flow of water without settling to the bottom. These particles are typically clay and silt, as they are small and light enough to stay suspended in the water column. Among the options provided, silt is the most likely particle size to make up a stream’s suspended load.
Gravel is too large to remain suspended and usually forms part of the bedload.
Clay is also small and can be suspended, but silt is more commonly the predominant material in the suspended load due to its slightly larger size and greater prevalence in many stream environments.
Why are urban areas susceptible to flash floods?
A) Oil, gasoline, and other auto fluids repel more water into the stream system
B) City sewers promote flooding of city streets and parking areas
C) A high percentage of the surface area is covered with cement, asphalt, and other impervious
materials
D) Construction materials promote rapid absorption of precipitation, which puts excess water
into the stream system
C) A high percentage of the surface area is covered with cement, asphalt, and other impervious materials.
What is the minimum velocity needed for a 0.8 mm sand particle transition from a state of
deposition to transportation?
A) 5 cm/sec
B) 1 cm/sec
C) 15 cm/sec
D) 23 cm/sec
A) 5 cm/sec
In fluvial environments, the velocity needed to initiate the movement of sediment particles, such as sand, depends on factors like particle size, flow depth, and water density. For a 0.8 mm sand particle, research and empirical studies generally indicate that the minimum velocity required to transition a particle from a state of deposition to transportation is around 5 cm/sec.
This value is based on the concept of critical shear stress or the flow velocity required to overcome the frictional forces holding the sand particles in place on the streambed. If the water velocity exceeds this threshold, the particles will begin to move and be transported downstream.
8) Compare and contrast the water velocity and type of streamflow in a rocky mountain stream
versus a silt-bottomed stream along the Gulf Coast
When comparing a Rocky Mountain stream and a silt-bottomed stream along the Gulf Coast, there are several key differences in both water velocity and streamflow type. These differences are largely driven by the topography, climate, sediment types, and flow dynamics in each region.
