Lab8_Rivers_LLL

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University of Nebraska, Omaha *

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1104

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Geography

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Feb 20, 2024

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Lab 8—River Behavior Variation 11 Questions Possible bonus points Goals and motivation for the lab Rivers are so important to humans and to the earth as a system, and so richly diverse in their character and behavior, and we know so much about them, that it was difficult to choose what to focus on in this lab, given all the possibilities. One important aspect is that rivers are like the blood of the terrestrial world, an arterial network that transports water, sediment, salts and other compounds dissolved in the water, and sometimes organisms. It is this flow that we are going to focus on for this particular lab, and specifically we are going to focus on characterizing the variation in flow of water and sediment. USGS Image of the Mississippi River drainage network. This is the land area from which water flows into the Mississippi River and eventually to the Gulf of Mexico, transporting the sediment that feeds the Mississippi delta. It also transports human contaminants introduced into the water along the river all the way to the Gulf, influencing the water quality and biologic activity there. Many of the contaminants serve as nutrients for the growth of marine microbes. The Gulf of Mexico and the Mississippi River are linked. Source: http://toxics.usgs.gov/hypoxia/mississippi/index.html Why focus on the variation in flow? For one thing, this is where natural hazard risk lies. Consider the following. The first piece of information often provided about something is its ‘average’ value. Humans, of course, have accommodated their behavior to fit ‘typical’ and/or average river behavior. Yet, in understanding natural systems it is the range of behavior , especially the extremes, that is of fundamental importance. After all, the poor soul who has his head in a lit oven and his feet in a bucket of ice is on average at a comfortable temperature. An average is not only an incomplete description of a variable phenomenon; sometimes, when presented in isolation, the average can be misleading. It is the extremes , often known as outliers, the very high flows, and the very low flows that are of concern in natural hazard risk assessment. For rivers the focus is on floods and droughts. How often do these types of events occur, and what specifically happens during them? What is the biggest or longest event possible? Such considerations are especially important to efforts at living sustainably. Sustainability by its fundamental nature takes a longer-term perspective, and a long perspective forces consideration of the outlier events, the less common but larger floods that one is likely to see in a longer time period. History, and the inappropriate human development of some river flood plains and of coastlines, tells us that this is a particularly hard perspective and lesson for people to take and learn. 1

From an ESS perspective there are related questions about the different size events, such as – what moves most of the sediment: the larger flood events, or the typical and more frequent, day- to-day type flows? It turns out that outlier events, the larger and rarer catastrophic events, can determine a lot of how a system operates in the long run. This theme will be reinforced and explored even further in the lab on coastal systems where we consider hurricanes. Satellite (LandSat) image of 2011 flood on the Missouri River (water in blue on this false color image). This flood was striking because it lasted so long and was driven by the convergence of a large snow pack in the Rocky Mountains and intense spring rains in the mountainous headwaters. The flooding was unusual in terms of the length of time it lasted (months instead of weeks or less). Image courtesy of NASA. For this lab you will choose an appropriate river in the central U.S. (Great Plains region) and learn about and report on the variation of water and sediment flow and possible reasons for that variation. The United States Geologic Survey (USGS) , a federal agency, maintains a country wide stream gauging network that feeds data from the gauging stations on the streams to an associated, real-time, on-line database that keeps track of rivers, and from which we will learn to find and extract information/data. Therefore, you will need to select a river that has gauging stations on it. Luckily, the network is extensive so you will have abundant possibilities from which to choose. We chose to focus on the Great Plains because UNO is located there, the rivers are very important to the local economy, and the rivers in this region show some interesting behavior. If your instructor permits, there is no reason you cannot choose a river elsewhere in the U.S. This lab has an open inquiry component to it in that you will choose the river you will focus on, and you will determine the exact time period of data you will look at. Results will differ among students. Experience suggests to us that some students may be uncomfortable with such open instructions at first, a response that may be amplified in an on-line setting. Yet, think about it – most real-life situations deal with open inquiry. Such open inquiry is arguably a truer form of exploration. Remember, it is OK to feel a bit lost at first, and your instructor can help when/if needed. Even after decades of practice under their belts, scientists often still feel lost when they first tackle a new project. Indeed, one goal of this lab in particular and the course in general is to make you more comfortable with open-ended explorations, which is an essential part of science. 2

Conceptual framework for thinking about river and sediment flow (3 pts) It may be helpful to review the tools that were addressed in your second lab that can be used to understand complex systems, such as rivers, and construct associated system diagrams for such systems. With such a perspective you can ask: what are the reservoirs, transfer processes, and variables that determine the flow of water at a point on a river? The amount of water flow is called the discharge , which has units of volume per unit time , and can be thought of as the volume of water that moves past a given point on a river over a specified amount of time. You can also describe the amount of sediment that the river is carrying in the same way—as sediment discharge . The units of sediment discharge are often mass per unit time (e.g. tons per day) instead of volume per unit time. Discharge naturally changes along the length of a river, usually (but not always) increasing downstream. This is because of new inflows or outflows that occur along the length of the river, the most obvious (but not only) of which is another river joining the river under consideration (e.g. the Platte River joining the Missouri River changes the water and sediment discharge downstream of their confluence). Basically, in this section of the lab we are looking in greater detail at part of the water cycle, and specifically the part dealing with surface water. However, it turns out that surface water is strongly linked to ground water, especially for rivers that flow over their own floodplains. What are the various reservoirs the water comes from? One can be snow pack or glacier ice up in the mountains that source the river and that melt in spring and summer. Another can be atmospheric moisture, otherwise known as rain. Yet another is groundwater (think of springs). For a lot of rivers in the U.S., another important reservoir is a dammed lake, where humans control the outflow for downstream river discharge. What are the various reservoirs the water can move to (i.e. what are some outflows)? The ocean is one obvious possibility. Inland lakes are another (think of the Great Salt Lake in Utah). Rivers can also leak water into the surrounding sediment and or bedrock, and so groundwater is another. Rivers can also lose water by evaporation, and by transpiration (where plants take water from the soil and then evaporate it) to the atmosphere. Significant amounts of river water are also diverted by humans for irrigation purposes. Some transfer processes include precipitation (snow and rain as two different possibilities), evaporation, melting, human control of dam releases, gravity induced flow, seepage into ground, spring flow, and irrigation withdrawals. Associated variables that influence the rate of transfer include: temperature, humidity, porosity (the percentage of space in sediment and rocks that water can move into) and permeability (the ability of water to move through sediment or rocks), ground surface slope, plant type. At this point you should open the companion PowerPoint file for this lab. This is a similar setup to the second lab, where you will use the components to assemble a system diagram, in this case, for the more focused reservoir—the water in a river upstream of a given point (e.g. upstream of a USGS gauging station). The resulting diagram will provide you with a conceptual model with which to think about the variation in water flow of a river. 3

Question 1: Insert a copy of your PowerPoint water flow system diagram below. Bonus exercise (optional, 3 pts) : Create a similar system diagram for the sediment discharge for a river, considering the movement of sediment through the system instead of water. Be as thorough as with the water flow diagram. Finding your way around the USGS National Water Information System (NWIS) For this exercise, you must first choose the river section you will explore. Picking a river that you have some connection with (you live near it or paddled on it) can make this lab more relevant to you. To choose your river section, go to the web site: http://waterdata.usgs.gov/nwis/rt . A map of the United States will appear with multiple “dots” of different colors. An example of such a map for the state of Nebraska is shown in the screen shot below. Screen shot of USGS map of gauging stations for Nebraska. The dots represent some of the monitoring stations that measure streamflow conditions in the United States and Puerto Rico. From here you can click on a state that you would like to retrieve water data from. A new page will open with a map of the state chosen to the left. Data is available for any “dot” (gauging station) that you can click on, but there is at least 30 years of data for the colored dots, and so you should choose one of these . Mousing over a dot brings up a small window that provides some information for that station. Clicking on one of the dots brings up a new page where you can select options for the type of data you want and the form in which it is presented. Up near the top of the page is a tab “Data Inventory” with a drop-down menu. The two data sets you will need to have access to in order to complete the exercise below are “Monthly Statistical Data” and “Peak Streamflow.” If your station doesn’t have data for both of these data sets, choose a different site. Once you have selected one of these options, a new window opens in which you check 4

which data you want from a list of what is available (discharge data in your case). If there are specific years that you are interested in you can limit the search; if left blank the entire time period available is returned. You also specify the form you want the data in. Most of the time, the “Table” option is the best, but if that doesn’t work when you Copy and Paste into your Excel sheet, you can try the “Tab-separated” option. When you are ready, click on “Submit,” after which a new window with the data you need should open up. You can Copy and Paste out of this. Screen shot of USGS window for one of the Nebraska river gauging stations showing the drop-down menu you can use to obtain the data you will need for this exercise. 5

Screen shot showing the window that opens when the monthly statistics option is chosen in the previous window. As you explore this website, you will notice that there are many options in this very extensive site, and you can acquire the same data through other paths. If you are having trouble getting to your data please contact the instructor . A tutorial that will teach you about the NWIS site can also be found at https://help.waterdata.usgs.gov/tutorials . Remember, that the web is a very dynamic place and updates and changes are constant, and different browsers also work differently, so it may be that the website doesn’t quite work as described above. However, the website contains instructions so that you can also learn to navigate it that way. If we need to update the above instructions please let us know. Before you actually extract and analyze data from the USGS site we first want you to learn more about the section of river you have chosen using Google Earth . This will help you understand the plots you create using the data. Learning about your river via Google Earth (3 pts) Open up Google Earth and navigate along your chosen section of river, looking for 4 elements/features along the river that could influence the water discharge or sediment discharge (a dam would be one obvious possibility). Copy an image (Edit  copy image) of each element/feature and insert it in below. Remember to turn on the scale indicator in Google Earth so that it will be included in your image. For each element/feature, describe in a couple of sentences how it influences sediment or water discharge (using the possibilities described above, or others you think of on your own). You should also feel 6

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