Reference no: EM132832484

Question 1

Lab 6: Stream Discharge

Introduction
On continents, streams are the primary means of transporting sediment, nutrients, and pollutants, and are also major agents of erosion and denudation, serving to move material from areas of high elevation to areas of lower elevation. Streams come in many shapes and sizes depending on a variety of factors, and can be as little as a backyard trickle and as large as (or larger than) the Mississippi River. Streams can also pose quite a hazard to society, as evidenced the U.S. government's National Flood Insurance Program run by FEMA (Federal Emergency Management Agency). In order to understand exactly how much erosion or flood damage streams are capable of, one of the first steps is to be able to measure the amount of water flowing in a stream and to assess how much this amount of water varies over time. This lab will introduce you to the concept of stream discharge, including how it is measured and how it can be used to assist in the calculation of flood probabilities that aid in flood mitigation strategies across the country.
When you have completed this lab, you should be able to:
1. Define the term discharge and explain how it is calculated.
2. Measure the physical characteristics of a stream that flows through the UConn campus.
3. Analyze historical river flow data and draw observations about peak annual discharge and recurrence interval.
4. Calculate the recurrence interval for a flood of a given magnitude.

Part I: Stream Discharge

The amount of water flowing at a point in a stream can be measured as:

Q = VxA

• Q = Discharge, or the volume of water moving through a stream at a given point and time.
• V = Velocity, typically determined with flow meters. Flow velocity can be estimated by timing how long it takes for a floating object to travel a set distance.
• A = Cross sectional area = depth x width. If the stream channel was a simple rectangle, this would be an easy calculation. However, the channel is more likely to be irregular so you will have to measure depth at several locations across the stream to obtain an accurate area value.

Stream discharge data is typically plotted on a hydrograph which shows how streamflow varies over time. An example of a hydrograph is shown later in this lab - it was produced using data from the Fenton River, which is located just east of campus (if you've ever hiked through the UConn forest, this is the river that some of the trails lead to). The US Geological Survey maintains a nationwide network of these stream gauging stations, and the data is publicly available at waterdata.usgs.gov!

QUESTION 2

Below is a series of aerial images showing stream channel complexity and variation in sediment composition (sand, cobbles, boulders, etc.) and vegetation. Images A & C show sandbars, while B & D have cobbles and boulders. Also images A & B have large woody debris (downed trees and branches) in channel while C has minimal in channel wood and none in image D. Vegetation in all images have a range of grass to shrubs to trees along " banks (although not uniform in distribution).

Have a look at the image of the stream channel in the Hangay Mountains. What materials make up the bed and banks of the stream channel? For example, does the stream channel appear to be in bedrock, gravel, sand or mud? Hint: use the top 4 examples as a guide for describing a stream channel, the more descriptive the better!

QUESTION 3

Examine the above diagram. It depicts a cross-section of a stream and the riffles and pools That have formed in its bed. Analyze the image and fill in the following blanks: Water would flow (faster, slower) over the riffles. In riffles water is (shallower, deeper), and bed material is
(finer, coarser).

Water would flew ____ (faster, slower) in the pools. In pools, water is _____ (shallower, deeper), and bed material is____(finer, coarser).

Water would flew ____ (faster, slower) in the pools. In pools, water is _____ (shallower, deeper), and bed material is____(finer, coarser).

QUESTION 4

Envision the hypothetical scenario:

You just bought a farm that has a creek running along the rear of the property. You'd like to use some of the creek water to irrigate your pumpkin patch, but you don't want to use too much water so that the creek runs dry and destroys the creek's ecosystem_ As a result, you set out to calculate the discharge of the creek so that the amount of water you use is only a small fraction of the total water running through the creek Here is a link for a similar scenario detailing the approach for measuring discharge

You don't want to spend money on any fancy equipment, so here's what you gather to measure the discharge:
• A 20-meter measuring tape.
• A meter stick_
• A stopwatch.
• Atennis ball.

First things first, you'll want to make some velocity measurements and record it in units of mis. In order to do so, you would need to use the ______ and ______.

In order to measure the width of the channel (you estimate it's about as wide the length of a car), you would use the ______.

In order to measure the depth (it does not surpass your knees), you would use the______.

QUESTION 5

Now imagine that the measurements you made allowed you to craft the diagram below (note that this is a cross-section!), and that you made multiple velocity measurements across the surface of the channel (with the dots representing flow out of the page). Using the diagram and velocity data; your task is to calculate the discharge of the stream in the cross section below. Note that measurements of surface velocity typically overestimate the true stream velocity, but let's assume this correction has already been made for the velocity data provided.

In order to measure the width of the channel (you estimate it's about as wide the length of a car), you would use the

In order to measure the depth (it does not surpass your knees), you would use the

QUESTION 6

Now imagine that the measurements you made allowed you to craft the diagram below (note that this is a cross-section!), and that you made multiple velocity measurements across the surface of the channel (with the dots representing flow out of the page). Using the diagram and velocity data, your task is to calculate the discharge of the stream in the cross section below. Note that measurements of surface velocity typically overestimate the true stream velocity, but lets assume this correction has already been made for the velocity data provided.

Robert's Brook is a semi-artificial stream on the Storrs campus that drains overflow from the Mirror Lake pond. Imagine that you were actually able to go out with your lab groups and measure flow in Robert's Brook, and that the table below lists the data that was reported for each group. Assume that Station 1 was closest to Mirror Lake, whereas Statmn 5 was the furthest downstream of the lake.

QUESTION 7
Using the table of data shown above, calculate the discharge in mils for each station. Enter your answer to 3 decimal places.

Station 1. Station 2: Station 3, Station 4, Station 5

QUESTION 8
Use the data and your calculations above from Robert's Brook to consider how cross sectional area, velocity, and cross sectional area changed as you moved downstream. Which of the following happened to velocity as you moved downstream from Station 1 to Station 5?
Decreased
Stayed approximately the same Increased

QUESTION 9

Use the data and your calculations above from Robert's Brook to consider how cross sectional area, velocity, and cross sectional area changed as you moved downstream. Which of the following happened to cross sectional area as you moved downstream from Station 1 to Station 5?

•  Decreased
•  Stayed approximately the same
• Increased

QUESTION 10

Use the data and your calculations above from Robert's Brook to consider how cross sectional area, velocity, and cross sectional area changed as you moved downstream. Which of the following happened to discharge as you moved downstream from Station 1 to Station 5?

• Decreased
• Stayed approximately the same
• Increased

QUESTION 11

Can you explain the most likely reason(s) for the variations in discharge along the stream? Comment specifically on what might cause the jump in discharge between stations 1-3 and stations 4-5.

QUESTION 12

Although Robert's Brook is fed by Mirror Lake, it's very similar to many other small streams around Storrs that have small drainage basins, or small areas that feed water into the streams. Most of the time it isn't raining, but most of these streams don't dry up, so where does the water in a stream come from? Make a list of potential sources below.

QUESTION 13

There is a US Geological Survey stream gauging station located not far from campus along the Fenton River, which is the river that Robert's Brook ultimately flows into. Data from this location is uploaded to the USGS website multiple times every day and the graph below shows how discharge varied at this location from June 1 - July 31, 2018

QUESTION 14

Peaks in the hydrograph represent ______ (increased, decreased) precipitation, and extremely high precipitation could cause the water to overtop the banks of the channel, resulting in _______ Valleys in the hydrograph represent (increased, decreased) precipitation, where the height of the water returns to baseflow conditions.

QUESTION 15
How many times did the discharge surpass a measurment of 30 cubic feet per second? (Note: discharge is displayed on a logarithmic

QUESTION 16
The discharge values on the graph for the Fenton River are much larger than those you measured for Robert's Brook. Why is there so much more water flowing down the Fenton River? (Hint: 'Because its a bigger river is not a sufficient answer Think instead about why it is a bigger river___)

QUESTION 17

Do you think that Fenton River discharge would ever go to zero? Why or why isn't this likely to happen?

QUESTION 18

Part II: Flood Frequency

Large floods can be extremely costly natural hazards in terms of both loss of property and loss of life. It is very challenging to predict exactly When a flood of a certain size may occur, However, we can use historical records of river discharge (from United States Geological Survey -USGS -stream gages) to approximate a Recurrence Interval for flood events both large and small. Frees the USGS

"Possibly you can remember when a really big rain storm hit your town. iffiood conditions occurred because of the rain then you might have heard the radio orTV weatherman say something like 'This storm has resulted in a soo-year flood on So-and-so Rivet; which had a discharge of so times normal values.. Obviously, this means that the river reached a discharge level that happens only once every sao years, right? Well, not exactly.

The term "too-year flood" can be misleading because it is often a misinterpretation of terminology that leads to a misconception of what a soo-year flood realty is. Instead of the term "soo-year flood. a geologist would rather describe this extreme hydrologic event as a flood having a soo-year recurrence interval, and since recurrence intervals are based On probabilities, this means that the So-and-so River reaching a discharge so times greater than normal is has a probability of occurring once in zoo years. in other words, a flood of that magnitude has a x percent chance of happeginny_year.'

For this exercise, we will determine the recurrence interval for the '3oo-year flood' an the Connecticut River near Hartford, CT and the Westfield River at Westfield, MA (this river ultimately flows into the Connecticut River). While the titling offloads is hard to predict, the probability offloading can be used by area managers to delineate what areas will be affected by floods of different magnitudes. The only surefire way of limiting potential loss of property and human life during flood events is to limit construction of businesses and homes within areas potentially affected by floods that will recur within timescales relevant to human lifetimes (los or Loos of years).

QUESTION 19

Shown below are two records of discharge data, one for the Connecticut River, and one for the Westfield River. Each plot shows the highest annual discharge recorded for each year on record for both of the rivers. Use these plots to

QUESTION 20

Shown below are two records of discharge data, one for the Connecticut River, and one for the Westfield River. Each plot shows the highest annual discharge recorded for each year on record for both of the rivers. Use these plots to

QUESTION 21

What is the largest discharge recorded for the Connecticut River?

• 2000 m³/s
• 4000 m³/s
• 7000 m³/s
• 9000 m³/s

QUESTION 22

What is the largest discharge recorded for the Westfield River?

• 2000 m³/s
• 4000 m³/s
• 7000 m3/5
• 9000 m3/s

QUESTION 23

In the table below, you have been provided with the six largest flood events on record for the CT River. To calculate the recurrence interval, use the following steps:

1. In the Rank Column, order the events from largest to smallest, and assign each event a rank from 1 to 6, with a rank of 1 corresponding to the largest discharge event, a rank of 2 corresponding to the second largest event, and so on.

2. Calculate the Recurrence interval for each year using the following equation:

RI = (N+1)/M

Where N is the number of observations, and M is the Rank assigned in Step 1

Note that this is a subset of data with only 6 observations. For the NI value, we are going to use the entire length of records for the Connecticut River, which is a total of 86 observations (years).

QUESTION 24

Enter in the calcuated recurrence interval for each of the events (round to the nearest year):
1933: 1936: 1938: 1955: 1960: 1984:

QUESTION 25
What is the probability of the largest flood on record occuring in any given year? (answer as a percent to two decimals)

QUESTION 26
Below is a plot of discharge vs. recurrence interval for the Westfield River. Analyze the data to choose the correct observation:

As discharge increases, recurrence interval decreases
As discharge increases, recurrence interval increases
As discharge decreases, recurrence interval increases

QUESTION 27
For the above plot, which of the following trendlines might you apply to predict recurrence intervals for larger discharge events?
linear trendline
exponential trendline
power law trendline

QUESTION 28
What is one way you would use what you've learned from this exercise to help people avoid flood hazards?

Attachment:- Lab Worksheet.rar