LAB 2: HYDROLOGIC CYCLE AND STREAMFLOW Overview: This lab co...

LAB 2: HYDROLOGIC CYCLE AND STREAMFLOW Overview: This lab consists of data analysis focused on the hydrologic cycle and streamflow measuring. It has two parts for a total of 88 marks: Part A: A Review of the Hydrologic Cycle [44 Marks] Part B: Streamflow Data Analysis [44 Marks] PART A: A Review of the Hydrologic Cycle [50 Marks] Objectives: To review components of the hydrologic cycle and causes for their spatial and temporal variability. Background: The hydrologic cycle describes the continuous movement of water between the atmosphere, land and water bodies (ocean, rivers, lakes, groundwater...). It is made up of various components which you have learned about in lecture and the course textbook. Cycling of water on Earth depends on the physical and chemical properties of the water and the medium through which it travels or interacts with. In addition to your course book, you can find more information about the hydrologic cycle here. Assignment: 1. Take a picture or make a sketch of an area around your home, at your favorite park, or from a fun recent vacation, and insert the following components of the hydrologic cycle into it. Each component should be represented by an arrow showing the direction of water movement: (note, the image included here is just for reference as a way to make your sketch/image) [6 marks] • Precipitation • Infiltration • Transpiration • Water table • Surface runoff • Percolation • Zone of aeration • Throughfall • Interception • Evaporation • Zone of saturation • Groundwater flow 2. Accompany your sketch with a definition of each component to the hydrological cycle listed in question 1 above – in your own words. [12 marks] 3. What is the key surface characteristic that determines whether rates of interception are high or low? Hint: in what case would interception be 0? [2 marks] 4. Is surface runoff more likely to occur on soils with a high permeability or a low permeability? Why? Please include a definition of permeability in the context of the hydrologic cycle. [4 marks] 5. Should the presence of vegetation increase or decrease the likelihood of infiltration? Explain. [4 marks] 6. Should rates of transpiration be greater in Laurel Creek Conservation Area in the summer or in the winter? Why? [2 marks] 7. Imagine the following scenarios for each of the following locations and state whether surface runoff and infiltration should be low, moderate or high, and briefly explain your choice. Go to the link to view the location in Google Maps – look at both the satellite imagery layer and the map layer by clicking on the square on the bottom left of the map window. You can also view terrain contours by clicking on the Menu button on the left-side toolbar and then clicking the terrain tab [3 marks each (15 marks in total)]. Infiltration Surface Runoff a) Ring Rd (UWaterloo campus), after a summer rainstorm b) Wooded, hilly areas in Southern Ontario, after a summer rainstorm c) Frozen, snow-covered, hilly areas in Grey County Ontario, after a winter rain d) Steep bedrock slopes, high in the Rocky Mountains of Alberta, after a summer rain e) Rolling hills of prairie grasslands, after a summer rainstorm PART B: Streamflow Data Analysis [44 Marks] Objectives: To gain practical experience in understanding streamflow data collection and analysis, and to gain a better understanding of differences and limitations among measurement techniques. Background: There are many different sizes of open water channels, from small headwater streams to rivers like the Grand River that flows through the Kitchener-Waterloo Region. The amount of water flowing past a certain point in an open channel, over a given time, is called stream flow or discharge. Discharge is measured as Q = U*A, where U equals the mean velocity of water in the channel and A is the cross-sectional area of the channel – in other words the area of the “slice” of stream flow which is being measured (see the figure below). Think…what should the units of river discharge be? Where should you measure U? What methods are available to measure the depth and width of the water, and how can we use those measurements to obtain A? This part of the lab allow you to confidently answer these questions! Streamflow measurements give us information about a stream’s velocity and volume, which in turn influence the ability of the stream to erode its bed and banks, transfer sediment, pollutants, and nutrients, and can help determine the physical habitat of the stream. Information on streamflow is also critical for flood management and prevention – field measurements and models form the basis of determining riparian flood zones. In this part of the lab, you will learn about different methods for obtaining stream discharge – from simple “float” methods, to mechanical, electromagnetic, and acoustic flow meters, to estimations from remotely piloted aircraft systems (RPAS or drones) and satellites. All stream gauging methods must involve finding water cross-sectional area (A) and velocity (U). In a simplified rectangular cross-section, A = depth*width, but in a natural river channel with a complex bed geometry, A must be found by breaking the area into easy-to-measure “chunks” of a known area. See above. For each chunk or section, a U value is obtained to find Q for the specific section. Then, all sections can be added to obtain total Q. The methods for measuring discharge you will learn about generally fit into two categories – direct measurements and indirect measurements. Direct measurements require placing a tool directly into the water, while indirection measurements can obtain parts of the discharge equation without touching the water. Notes: Remember that since this is an online course, you are free to use online resources to help answer the questions. If you do, please cite the source you used. ***Please also turn in your excel spreadsheet so we can give partial credit to work done partially correctly*** Streamflow Questions 1. One of the oldest (but still effective!) ways of measuring river velocity is by using the “float” method. Assume that the channel cross-section is trapezoidal (often a decent approximation of a river channel). Using the Lab 2 Data handout on the Float Method tab, answer the following questions. a. Fill out the blue-highlighted cells to find U and Q for tests 2-5. Paste the filled-in values here, including the units for both U and Q. [2 marks] b. Are there any U and/or Q values that you feel are not reliable? If so, which test might you discard and why? [2 marks] c. Think of and explain one reason why a specific test using the float method might produce a U value that is much different than the other tests. Hint: if you were in a tube or kayak moving down a river, could you move unimpeded forever? [2 marks] d. Typically, flow velocity is higher at the water surface than on average throughout the channel and often a velocity correction factor is used. Surface velocity is multiplied by 0.85-0.9 to account for this – why do you think surface velocity is lower than average velocity? [2 marks] 2. A more advanced, but similar, way of using surface velocity to aid in the computation of discharge is with image velocimetry techniques. A video or series of images of the river is obtained, and the movement of tracer particles is used to define velocity. In this video, particles that have red tracks are moving faster than those with blue tracks (they move a larger distance over the same time interval). Recently, using image velocimetry has gained favor for measuring Q because it can be integrated with RPAS or mounted cameras and is often less expensive than traditional techniques. Using the Lab 2 Data handout on the Image Velocimetry tab, answer the following questions. a. What is the average depth of the water in this case? [1 mark] b. What is the average velocity of the water in this case? [1 mark] c. Using the average velocity and the average depth, what is the discharge, (Q)? [1 mark] d. Using a left-hand Riemann Sum, find the area associated with each chunk/section that we have obtained velocity for. The first few cells have been done for you. Then, using the velocity and area for each section, find the total discharge Q. [2 marks] e. How does your value for part c compare to your value for part d? Which value do you think is more accurate? Explain at least one reason why the values are not the same. [3 marks] f. Image velocimetry allows one to obtain velocity simply from videos and pictures. Is this an indirect method or a direct method of obtaining discharge, and why? Explain one situation where using an indirect method of obtaining discharge might be preferable compared to using a direct method. [2 marks] 3. The same concepts from part B-2 apply for mechanical, acoustic, or electromagnetic current meters that one must deploy in the flow – width and depth are used to create an average area for a section, which is multiplied by a velocity value to obtain Q in said section. These methods use the force of the water to turn a propeller (mechanical), a measured electric field (electromagnetic), or the Doppler shift principle (acoustic) to obtain velocity at specific points within a river. All these point-based measurement tools require the tool to be deployed in the river, where it measures depth and velocity at numerous locations (distances across the cross section). a. Are these measurements direct or indirect, and why? [2 marks] b. Explain one situation where direct measurement might be preferable compared to using an indirect method. [2 marks] 4. A typical modern way of obtaining river discharge is with a self-contained tool called an acoustic Doppler current profiler (ADCP). ADCPs are able to obtain velocity, depth, and width at the same time by using Doppler shift principles. In essence – the ADCP yells really loudly, listens to how that sound bounces back to it, and can then determine where the river bed is (very loud reflection!), how fast flow is moving (pitch shifts due to sound bouncing off particles in the water moving a certain direction), and where the tool itself is (integrated GPS info). Using the Lab 2 Data handout on the ADCP tab, answer the following questions. a. Explain one advantage of the ADCP over the previous methods of stream gauging we have discussed. [2 marks] b. Explain one potential disadvantage of using the ADCP. [2 marks] c. Plot distance vs. depth, as a scatter plot and paste it here. Generally, where is depth the greatest and where is it the lowest? [2 marks] d. Plot distance vs. velocity, as a scatter plot and paste it here. Generally, where is velocity greatest and where is it lowest? [2 marks] e. The ADCP measures every second, and thus the distance spacing of each measurement depends on how fast the instrument moves across the channel. With this in mind, which of the above methods would make most sense to use for calculating the discharge, Riemann Sums or taking an average width and depth? [2 marks] f. Using your preferred method, what is the discharge of this river? [1 mark] 5. One efficient way of obtaining discharge is by measuring both river depth and river discharge and relating them to each other. Once a relationship between depth (also known as stage) and discharge is established, one must only measure depth and infer discharge from the equation that describes the relationship. Measuring average depth of a river is often much easier than measuring discharge, and this process is called establishing a “rating curve”. Using the Lab 2 Data handout on the Rating Curve tab, answer the following questions. a. Why might is be easier to only measure depth and width, rather than discharge? [2 marks] b. Plot stage on the y-axis and discharge on the x-axis. Fit a curve to the plot – go here for more information on how to fit a curve to a plot. What is a better fit to the data, a power function or a linear function, and how do you know? Include the functions below with their R2 values. [3 marks] c. Using the function you think fits best to the data, fill out the blue highlighted cells in the Function Fitting table and paste them here. HINT – from question 5-b above, you will produce an equation in the form y = x (with some computation that must be done to x). The point of a rating curve is to only measure x, so x = stage. Solve for y. [2 marks] d. Assume that after a large flood you find your stage recorder shows the creek was 5 meters deep at one point. When you constructed your rating curve, the largest stage you measured was about 2.5 m deep. Do you think using the rating curve to estimate Q at a 5 m stage is appropriate? Why or why not? [2 marks] e. How might indirect measurements of discharge and velocity from a remotely piloted aircraft of a satellite improve the ability of rating curves to characterize floods with large stage and Q values? [2 marks]