Unit 8 Lab Running Water, Groundwater, and Ocean Processes Fall 23

.pdf

School

Georgia Military College *

*We aren’t endorsed by this school

Course

1GG

Subject

Geography

Date

Dec 6, 2023

Type

pdf

Pages

25

Uploaded by Teresawes

Report
UNIT 8: RUNNING WATER, GROUNDWATER, AND OCEAN PROCESSES Randa Harris and Brianne Smith I NTRODUCTION Think how many times a day you take water for granted – you assume the tap will be flowing when you turn on your faucet, you expect rainfall to water your lawn, and you may count on water for your recreation. Not only is water necessary for many of life’s functions, it is also a considerable geologic agent. Water can sculpt the landscape dramatically over time both by carving canyons as well as depositing thick layers of sediment. Some of these processes are slow and result in landscapes worn down over time. Others, such as floods, can be dramatic and dangerous. What happens to water during a rainstorm? Imagine that you are outside in a parking lot with grassy areas nearby. Where does the water from the parking lot go? Much of it will run off as sheet flow and eventually join a stream. What happens to the rain in the grassy area? Much of it will infiltrate, or soak into the ground. We will deal with surface and ground water in this lab, as well as ocean processes. All are integral parts of the water cycle, in which water gets continually recycled through the atmosphere, to the land, and back to the oceans. This cycle, powered by the sun, operates easily since water can change form from liquid to gas (or water vapor) quickly under surface conditions. Both surface and ground water are beneficial for drinking water, industry, agriculture, recreation, and commerce. Demand for water will only increase as population increases, making it vital to protect water sources both above and below ground. Learning Outcomes: After completing this chapter, you should be able to: • Understand how streams erode, transport, and deposit sediment • Know the different stream drainage patterns and understand what they indicate about the underlying rock • Explain the changes that happen from the head to the mouth of a stream • Understand the human hazards associated with floods • Know the properties of groundwater and aquifers • Understand the distribution of groundwater, including the water table • Learn the main features associated with karst topography • Understand the challenges posed by karst topography Key Terms: Drainage basin Drainage pattern Drainage divide Stream gradient Permeability Porosity Discharge Natural levee Aquifer
Karst topography Floodplain Entrenched meander S TREAMFLOW AND P ARTS OF A S TREAM The running water in a stream will erode (wear away) and move material within its channel, including dissolved substances (materials taken into solution during chemical weathering). The solid sediments may range in size from tiny clay and silt particles too small for the naked eye to view up to sand and gravel sized sediments. Even boulders have been carried by large flows. The smaller particles kept in suspension by the water’s flow are called suspended load. Larger particles typically travel as bed load, stumbling along the stream bed (Figure 1). While the dissolved, suspended, and bed loads may travel long distances (ex. from the headwaters of the Mississippi River in Minnesota to the Gulf of Mexico at New Orleans), they will eventually settle out, or deposit. These stream deposited sediments, called alluvium, can be deposited at any time, but most often occur during flood events. To more effectively transport sediment, a stream needs energy. This energy is mostly a function of the amount of water and its velocity, as more (and larger) sediment can be carried by a fast-moving stream. As a stream loses its energy and slows down, material will be deposited. Under normal conditions, water will remain in a stream channel. When the amount of water in a stream exceeds it banks, the water that spills over the channel will decrease in velocity rapidly due to the greater friction on the water. As it drops velocity, it will also drop the larger sandy material it is carrying right along the channel margins, resulting in ridges of sandy alluvium called natural levees (Figure 2). As numerous flooding events occur, these ridges build up under repeated deposition. These levees are part of a larger landform known as a floodplain . A floodplain is the relatively flat land adjacent to the stream that is subject to flooding during times of high discharge (Figure 2). Figure 1. An illustration depicting dissolved, suspended, and bed load. Author: User "PSUEnviroDan" Source: Wikimedia Commons License: Public Domain
Figure 2. The creation of natural levees over time. Author: Julie Sandeen Source: Wikimedia Commons License: CC BY-SA 3.0 S TREAM D RAINAGE B ASINS AND P ATTERNS The drainage basin of a stream includes all the land that is drained by one stream, including all of its tributaries (the smaller streams that feed into the main stream). You are in a drainage basin right now. Do you know which one? You can find out on the internet. Go to the Environmental Protection Agency’s webpage (epa.gov) and search for Surf Your Watershed to find out. The higher areas that separate drainage basins are called drainage divides. For North America, the continental divide in the Rocky Mountains separates water that drains to the west to the Pacific Ocean from water that drains to the east to the Gulf of Mexico. As water flows over rock, it is influenced by it. Water wants to flow in the area of least resistance, so it is attracted to softer rock, rather than hard, resistant rock. This can result in characteristic patterns of drainage. Some of the more common drainage patterns include: • Dendritic – this drainage pattern indicates uniformly resistant bedrock that often includes horizontal rocks. Since all the rock is uniform, the water is not attracted to any one area, and spreads out in a branching pattern, similar to the branches of a tree. • Trellis – this drainage pattern indicates alternating resistant and non-resistant bedrock that has been deformed (folded) into parallel ridges and valleys. The water is attracted to the softer rock, and appears much like a rose climbing on a trellis in a garden.
• Radial – this drainage pattern forms as streams flow away from a central high point, such as a volcano, resembling the spokes in a wheel. • Rectangular – this drainage pattern forms in areas in which rock has been fractured or faulted which created weakened rock. Streams are then attracted to the less resistant rock and create a network of channels that make right-angle bends as they intersect these breaking points. This pattern will often look like rectangles or squares. • Deranged – this drainage pattern does not follow the rules. It consists of a random pattern of stream channels characterized by irregularity. It indicates that the drainage developed recently and has not had time to form one of the other drainage patterns yet. Figure 3. Drainage patterns. Author: Corey Parson Source: Original Work License: CC BY-SA 3.0
S TREAM G RADIENT A ND T HE C YCLE O F S TREAM E ROSION Stream gradient refers to the slope of the stream’s channel, or rise over run. It is the vertical drop of the stream over a horizontal distance. You have dealt with gradient before in Topographic Maps. It can be calculated using the following equation: Gradient = (change in elevation) / distance Let’s calculate the gradient from A to B in Figure 4 below. The elevation of the stream at A is 980’, and the elevation of the stream at B is 920’. Use the scale bar to calculate the distance from A to B. Gradient = (980’ – 920’) / 2 miles, or 30 feet/mile. Figure 4 . Gradient calculation. Stream gradients tend to be higher in a stream’s headwaters (where it originates), and lower at their mouth (where they discharge into another body of water, such as the ocean). Discharge measures stream flow at a given time and location, and specifically is a measure of the volume of water passing a particular point in a given period of time. It is found by multiplying the area (width multiplied by depth) of the stream channel by the velocity of the water, and is often in units of cubic feet (or meters) per second. Discharge increases downstream in most rivers, as tributaries join the main channel and add water. Sediment load (the amount of sediment carried by the stream) also changes from headwaters to mouth. At the headwaters, tributaries quickly carry their load downstream, combining with loads from other tributaries. The main river then eventually deposits that
sediment load when it reaches base level. Sometimes in this process of carrying material downstream, the sediment load is large enough that the water is not capable of supporting it, so deposition occurs. If a stream becomes overloaded with sediment, braided streams may develop, with a network of intersecting channels that resembles braided hair. Sand and gravel bars are typical in braided streams, which are common in arid and semiarid regions with high erosion rates. Less commonly seen are straight streams, in which channels remain nearly straight, naturally due to a linear zone of weakness in the underlying rock. Straight channels can also be man-made, in an effort at flood control. Streams may also be meandering, with broadly looping meanders that resemble “S”- shaped curves (Figure 5). The fastest water traveling in a meandering stream travels from outside bend to outside bend. This greater velocity and turbulence lead to more erosion on the outside bend, forming a featured called a cut bank. Erosion on this bank is offset by deposition on the opposite bank of the stream, where slower moving water allows sediment to settle out. These deposits are called point bars. As meanders become more complicated, or sinuous, they may cut off a meander, discarding the meander to become a crescent-shaped oxbow lake. Check out Figure 6 to see the formation of an oxbow lake. Figure 5. Parts of a meandering stream. The S-curves are meanders. The arrows within the stream depict where the fastest water flows. That water erodes the outside bank, creating a steep bank called the cut bank. The slowest water flows on the inside of the meander, slow enough to deposit sediment and create the point bar.
Your preview ends here
Eager to read complete document? Join bartleby learn and gain access to the full version
  • Access to all documents
  • Unlimited textbook solutions
  • 24/7 expert homework help