Stream morphology

Stream Morphology Investigation Manual

ENVIRONMENTAL SCIENCE

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STREAM MORPHOLOGY

Overview Students will construct a physical scale model of a stream system to help understand how streams and rivers shape the solid earth (i.e., the landscape). Students will perform several experiments to determine streamflow properties under different conditions. They will apply the scientific method, testing their own scenarios regarding human impacts to river systems.

Outcomes • Design a stream table model to analyze the different

characteristics of streamflow. • Explain the effects of watersheds on the surrounding

environment in terms of the biology, water quality, and economic importance of streams.

• Identify different stream features based on their geological formation due to erosion and deposition.

• Develop an experiment to test how human actions can modify stream morphology in ways that may, in turn, impact riparian ecosystems.

Time Requirements Preparation ...................................................................... 5 minutes, then let sit overnight Activity 1: Creating a Stream Table ................................ 60 minutes Activity 2: Scientific Method: Modeling Human Impacts

on Stream Ecosystems .................................. 45 minutes

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Key Personal protective equipment (PPE)

goggles gloves apron follow link to video

photograph results and

submit

stopwatch required

warning corrosion flammable toxic environment health hazard

Key Personal protective equipment (PPE)

goggles gloves apron follow link to video

photograph results and

submit

stopwatch required

warning corrosion flammable toxic environment health hazard

Table of Contents

2 Overview 2 Outcomes 2 Time Requirements 3 Background 9 Materials 10 Safety 10 Preparation 10 Activity 1 12 Activity 2 13 Submission 13 Disposal and Cleanup 14 Lab Worksheet 18 Lab Questions

Background A watershed is an area of land that drains any form of precipitation into the earth’s water bodies (see Figure 1). The entire land area that forms this connection of atmospheric water to the water on Earth, whether it is rain flowing into a lake or snow soaking into the groundwater, is considered a watershed.

Water covers approximately 70% of the earth’s surface. However, about two-thirds of all water is impaired to some degree, with less than 1% being accessible, consumable freshwater. Keeping watersheds pristine is the leading method for providing clean drinking water to communities, and it is a high priority worldwide. However, with increased development and people flocking toward waterfront regions to live, downstream communities are becoming increas- ingly polluted every day.

From small streams to large rivers (hereafter considered “streams”), streamflow is a vital part of understanding the formation of water and landmasses within a watershed. Under- standing the flow of a stream can help to deter- mine when and how much water reaches other areas of a watershed. For example, one of the leading causes of pollution in most waterways across the United States is excessive nutrient and sediment overloading from runoff from the landmasses surrounding these waterways. Nutrients such as phosphorus and nitrogen are prevalent in fertilizers that wash off lawns and farms into surrounding sewer and water systems. This process can cause the overpro- duction of algae, which are further degraded by bacteria. These bacteria then take up the surrounding oxygen for respiration and kill multiple plants and organisms. A comprehen- sive understanding of the interaction between streams and the land as they move downstream to other areas of a watershed can help prevent pollution. One example is to build a riparian buffer—a group of plants grown along parts of a stream bank that are able to trap pollutants and absorb excessive nutrients; this lessens the effects of nutrient overloading in the streambed. (A riparian ecosystem is one that includes a stream and the life along its banks.)

Sediment, which is easily moved by bodies of water, has a negative effect on water quality. It can clog fish gills and cause suffocation, and the water quality can be impaired by becoming very cloudy because of high sediment flow. This can create problems for natural vegetation growth by obstructing light and can prevent animals

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Figure 1.

Snow

Rainfall

Precipitation

Overland flows

Underground sources

STREAM MORPHOLOGY

Background continued from visibly finding their prey. Erosion also has considerable effects on stream health. Erosion, or the moving of material (soil, rock, or sand) from the earth to another location, is caused by actions such as physical and chemical weath- ering (see Figure 2). These processes loosen rocks and other materials and can move these sediments to other locations through bodies of water. Once these particles reach their final destination, they are considered to be depos- ited. Deposition is also an important process because where the sediment particles end up can greatly impact the shape of the land and how water is distributed throughout the system (see Figure 2). Erosion and deposition can occur multiple times along the length of a stream and can vary because of extreme weather, such as flooding or high wind. Over time, these two processes can completely reshape an area,

causing the topography, or physical features, of an entire watershed to be altered. Depending on weather conditions, a streambed can be altered quite quickly. Faster moving water tends to erode more sediment than it deposits. Deposi- tion usually occurs in slower moving water. With less force acting on the sediment, it falls out of suspension and builds up on the bottom or sides of the streambed.

Sediments are deposited throughout the length of a stream as bars, generally in the middle of a channel, or as floodplains, which are more ridgelike areas of land along the edges of the stream. Bars generally consist of gravel or sand- size particles, whereas floodplains are made of more fine-grained material. Deltas (see Figure 3) and alluvial fans (see Figure 4) are sediment deposits that occur because of flowing water

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Figure 2. Figure 3.

Erosion Deposition

and are considered more permanent struc- tures because of their longevity. They are both fan-shaped accumulations of sediment that form when the stream shape changes. Deltas form in continuous, flowing water at the mouth of streams, whereas alluvial fans only form in streams that flow intermittently (when it rains or when snow melts). Alluvial fans are usually composed of larger particles and will form in canyons and valleys as water accumulates in these regions. The fan shape of both deposits is easy to spot from a distance, because they are formed due to the sand settling out on the bottom of the streams.

Streamflow Characteristics Discharge, or the amount of water that flows past a given location of a stream (per second), is a very important characteristic of stream- flow. Discharge and velocity (the speed of

the water moving in the stream) are both vital to the shaping of streambeds. Within stream ecosystems, there are microhabitats (smaller habitats making up larger habitats) that have different discharges and velocities. The type of microhabitat depends on the width of that part of the stream, the shape of the streambed, and many other physical factors. In areas that contain riffles, water quickly splashes over shallow, rocky areas, which are easily observed in sunny areas (see Figure 5). Deeper pools of slower moving water also form on the outside of the bends of the streams, as shown in Figure 5. Runs, which are deeper than riffles but have a moderate current, connect riffles and pools throughout the stream. The source of a stream

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Figure 4.

Figure 5.

PoolRiffles

STREAM MORPHOLOGY

Background continued is where it begins, while the mouth of a stream is where it discharges into a lake or an ocean.

Flow rate is very helpful for engineers and scientists who study the impacts of a stream on organisms, surrounding land, and even recreational uses such as boating and fishing. The speed of the water in specific areas helps to determine the composition of the substrate in that area of the streambed, i.e., whether the material is more clay, sand, mud, or gravel. Particle sizes of different sediments are shaped and deposited throughout various areas of a stream, depending on these factors.

Most streams have specific physical features that show periodicity or consistency in regular

intervals. Meanders can occur in a streambed because of gravity. Water erodes sediment to the outside of a stream and deposits sediment along the opposite bank, forming a natural weaving or “snaking” pattern. This pattern can form in any depth of water and along any type of terrain. Sinuosity is the measure of how curvy a stream is. This is a helpful measurement when determining the flow rates of streams because it can show how the curves affect the water velocity. In major rivers and very broad valleys, meanders can be separated from the main body of a river, leaving a U-shaped water body known as an oxbow lake (see Figure 6). These lake formations can become an entirely new ecosystem with food and shelter for some organisms, such as amphibians, to thrive in.

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Figure 6.

Oxbow Lake Formation

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Another feature important for streamflow is the difference in elevation, or the relief of a stream as it flows downstream. Streams start at a higher elevation than where they end up; this causes the discharge and velocity at the source versus that at the mouth of the stream to be quite different, depending on the meandering of the stream and the type of deposition and erosion that occurs. The gradient is another important factor of stream morphology. This is a measure of the slope of the stream over a particular distance (the relief over the total distance of the stream). For a kayaker who wants to know how fast he/she can paddle down a particular stream, knowing the difference in elevation (relief) is important over a particular area; however, knowing the slope of this partic- ular area will give the kayaker a more accurate prediction. With erosion and deposition occur- ring at different rates and at different parts of the stream, knowing the gradient is a very important part of determining streamflow for the kayaker.

Groundwater is also affected by changes in the stream shape and flow. Water infiltrates the ground in recharge zones. If streams are contin- uously flowing over these areas, the ground is able to stay saturated. Most streams are peren- nial, meaning they flow all year. However, a drought or an extreme weather event may lower the stream level. This can lower the ground- water level, which then allows the stream to only sustain flow when it rises to a level above the water table. With the small amount of available freshwater on Earth, it is vital that our ground- water sources stay pristine.

Biotic and Economic Impacts of Streams Not only are streams a major source of clean

freshwater for humans, but they are also a hotspot for diversity and life. There is great biotic variability between the different microhabitats (e.g., riffles, pools, and runs) of a stream. Riffles, in particular, have a high biodiversity because of the constant movement of water and replenish- ment of oxygen throughout. Pools usually have fewer and more hardy organisms in their slower, deeper moving waters where less oxygen is available. There are also a multitude of plant and animal species living around streams. From a stream in a backyard to the 1,500-mile-long Colorado River, streams have thousands of types of birds, insects, and plants that live near them because they are nutrient-rich with clean freshwater. Sometimes nutrient spiraling can occur in these streams. Nutrient spiraling is the periodic chemical cycling of nutrients throughout different depths of the streams. This process recycles nutrients and allows life to thrive at all depths and regions of different-size streams.

Streams can also have significant economic impacts on a region. Streams are a channel for fishing and transportation, two of the largest industries in the world. Because of all the commercial boating operations that occur world- wide in these channels, it is vital to understand the formation and flow patterns of streams so that they are clear and navigable. Fishing for human consumption is another large, worldwide industry that depends on stream health; keeping streams pristine and understanding how they form are of utmost importance in sustaining this top food industry. Recreational activities such as kayaking, sportfishing, and boating all shape areas where streams and rivers are prevalent as well.

STREAM MORPHOLOGY

Background continued All acts that happen on land affect the water quality downstream. Through creating a model stream table in this lab, one can predict large, system-wide effects. Many land features and physical parts of a streambed can affect the flow of water within a watershed. Houses along a streambed or numerous large rocks can cause the streamflow to change directions. If any of these factors cause erosion or deposition in an area of the stream, microhabitats can be created. These factors can affect the stream on a larger scale, creating changes in flow speeds and widths of the streambeds.

The Importance of Scaling and the Use of the Scientific Method When a stream table model is created, a large- scale depiction of a streambed is being reduced to a smaller scale so that the effects of different stream properties on the surrounding environ- ment can be demonstrated. While the stream table made in this lab is not a to-size stream and landscape, the same processes can be more easily observed at a scaled-down size. Scientists frequently create models to simplify complex processes for easier understanding. For example, to physically observe something that is too big, such as the distance between each planet in the solar system, the spatial distance can be scaled to create a solar system model. By changing the distance between each planet from kilometers to centimeters, this large system is now more feasibly observed. Similarly, the stream model allows us to physically view different scenarios of a streambed and analyze different stream properties. Mathematical equations are also used frequently to observe

data to predict future conditions, such as in meteorological models. Ultimately, models can be very important tools for predicting future events and analyzing processes that occur in a system.

When one creates a model, many different outcomes for the same type of setup can be possible. In this case, multiple variations of similar-size streambeds will be designed to evaluate different stream features and their impacts on the surrounding ecosystem. When performing any type of scientific evalua- tion, the scientific method is very useful in obtaining accurate results. This method involves performing experiments and recording observa- tions to answer a question of interest.

Although the exact step names and sequences sometimes vary a bit from source to source, in general, the scientific method begins with a scientist making observations about some phenomenon and then asking a question. Next, a scientist proposes a hypothesis—a “best guess” based upon available information as to what the answer to the question will be. The scientist then designs an experiment to test the hypothesis. Based on the experimental results, the scientist then either accepts the hypothesis (if it matches what happened) or rejects it (if it doesn’t). A rejected hypothesis is not a failure; it is helpful information that can point the way to a new hypothesis and experiment. Finally, the scientist communicates the findings to the world through presenting at a peer-reviewed academic conference and/or publishing in a scholarly journal like Science or Nature, for example.

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When creating stream table models, we are trying to understand how different factors can affect streamflow. A few very important steps from the scientific method are required. The first is forming a testable hypothesis, or an educated prediction, of what you expect to observe based on what you have learned about stream morphology thus far. In Activity 1, the steps are already listed, so the main goal is to compare the two differences in stream reliefs. However, in Activity 2, the goal is to alter a different vari- able and predict what will happen to several stream features in this new situation. In general, when recording these observations to test a hypothesis, it is important to repeat the tests. To obtain valid results, you need to have similar results over multiple attempts to ensure consis- tency in the findings and to show that what you are discovering is not by chance but is instead replicated each time the experiment is run. While multiple trials are not required in this lab experi- ment, if you feel particularly less than confident with your results from doing only one trial run in Activity 1 or 2, feel free to do multiple trials to test for validity.