0.3 Lab no. 3: stream and channel measurements  (Page 3/3)

Site 2:

(1) Estimated vertical difference between bankfull and current water level for each side of the stream;

(2) Estimated Manning’s “n” and calculated discharge using Manning's formula for: (a) current water level; and (b) bankfull discharge;

(3) Stream classification according to both Rosgen and Montgomery-Buffington, and the values for each of the criteria in the Rosgen classification at each site to the extent they can be identified (i.e., bankfull width; bankfull depth; width/depth ratio; entrenchment ratio; etc.);

(4) Stream gradient as measured with the clinometer.

Reports (due october 25)

For this lab you will submit both a team and an individual report, and these are described below. You should read and reference the appropriate sections of the reader, as some of the questions will require a deeper understanding of the procedures used to collect your data and the resulting uncertainties.

With regard to the team report, it is important that your answers be formulated as a group, as that is the only way that each team member can become familiar with all the issues and topics associated with this lab. If you already have considerable experience in this type of work, please don't take over or attempt to dominate your group; most learning takes place as people grapple with a problem, and the least experienced gain the most from helping to develop the answers to each of the following questions.

Group report

Site 1

1. (a) Make a table comparing the velocities measured at the deepest point in the stream using the following techniques: (1) velocity at 0.6 times the depth; (2) mean velocity using 0.2 and 0.8 times the depth; (3) mean velocity using all depths; (4) float times 0.85; and (5) the velocity head method. (b) Comment on the relative reliability of each of the five techniques used to measure velocity, and then indicate which technique(s) would you recommend, and which are unreliable. Be sure to justify your answers.

2. Provide a final plot of your surveyed cross-section.

3. (a) What was your measured discharge? (b) How did your value compare to the other discharge measurements? (c) Using the information presented in class and the reader, list—in order of importance—the most likely reasons for the variability in the measured discharge values among groups. Briefly explain and justify your list.

4. (a) Provide a final plot of your particle-size distribution. (b) From this plot or the raw data list your D16, D50, and D84 values. (c) How do your values compare to the values obtained at the other cross-sections? (d) Using the material in the reader (e.g., Wolman, 1954; Platts et al., 1983) and presented in class, do you think that your data accurately represent the true distribution of particle sizes on the channel bottom at your cross-section? Briefly explain why or why not.

5. (a) What was your estimated value for Manning's n? (b) Show your calculations to estimate the discharge using Manning's equation. (c) Compare your calculated discharge to the measured discharge. (d) Rearrange and solve Manning's equation for n using your measured discharge (i.e., what value would Manning's n have to be for the calculated discharge to equal the measured discharge?). (d) In cases where we do not have a gaging station, the discharge associated with extreme events is typically estimated using Manning’s equation. Comment on the usefulness and accuracy of Manning's equation to estimate large flow events.

7. (a) What is your channel classification according to Rosgen (1994)? (b) What is your channel classification according to Montgomery and Buffington (1993, 1997)?

Site 2:

1. Provide a final plot of your surveyed cross-section.

2. (a) What was your estimated value for Manning's n? (b) Show your calculations to estimate the discharge using Manning's equation.

7. (a) What is your channel classification according to Rosgen (1994)? (b) What is your channel classification according to Montgomery and Buffington (1993, 1997)?

Individual reports

1. For site 2, comment on your ability to distinguish bankfull, and the likely accuracy of the bankfull values estimated by your group.

2. Comment on the current condition of the stream. Is it aggrading (sediment being deposited) or incising? Are the banks actively eroding? Does the stream look healthy to you? Why or why not? (I realize this is not an easy question, but please try. You should write somewhere between one paragraph and about one page.)

3. Attach your individual sketch map for site 2. Note that the two main purposes of a sketch map are: (1) to allow you or another observer to find the reach and locations where specific data were collected; and (2) document the current features of interest so that your or another observer could come back at a later date and determine whether there have been significant changes in the channel or adjacent riparian zones.