Key Concepts in Geomorphology – ideas for revision
Chapter 7 – Basins
Please add your comments about how to improve Chapter 7 here.
19 thoughts on “Chapter 7 – Basins”
Few more comments:
1. One thing that feels like it is missing from this chapter is any mention of deltas. Estuarine channels are mentioned, but not deltas. I would at least mention that they exist and note that they will show up in full force in ch. 8. It is hard to discuss sources and sinks of sediment without mentioning deltas.
2. There are a number of specific examples given (ex. p. 239: road cuts along White Mountains and Sierra Nevada; or terraces near the Grand Tetons) to illustrate points, but then there are not any photos of those sites. For readers unfamiliar with the locations, these points are not always helpful. If you want to refer to an iconic landscape, put in a picture that shows that iconic landscape with the geomorphic feature you are trying to explain. Or simply refer to them as “road cuts into fans near the base of active mountains” or “large valleys downstream from glaciated mountain ranges”, etc. Many students have never been out west, and actually seeing images of these landscapes in the context of what the geomorphology means might be more powerful.
3. Terraces. On p. 235, there is a line “For terraces to form, floodplain abandonment must be an episodic rather than gradual process.” is not technically true, as unpaired terraces can form due to lateral migration in the presence of overall downcutting. And on p. 237, this is noted at the end of the second paragraph.
4. Box 7.1 has a few issues. Dz/dx is not formatted properly in the equations, and it looks like x and xd are used interchangeably at times?
5. Overall, some of the figures use linear plots, some use log-log plots that are clearly labeled, and some use log-log plots but they are not labeled as such. I would go back and double-check them all to make sure that they are clearly labeled.
6. An earlier comment of mine pointed out the desire to have some verbage on the problem of sediment delivery in larger and larger watersheds, and ah ha! There is it in Digging Deeper. Thanks!
Few more figure comments:
Photo 7.7 notes that “The bar may eventually become vegetated and incorporated into the floodplain.” You could add the other possibility… or it may be remobilized during the next big flood and transported farther downstream.
Photo 7.9 is a bit washed out.
Photo 7.12b is pretty dark.
Photo 7.15 shows a strath terrace nicely. I don’t think Photo 7.14 is necessary.
Photo 7.16 – if you have a photo of a fill terrace that also shows the wide flat top of the terrace better, that would be good.
Photo 7.20 is too dark, making it hard to see the internal structure of the deposit. Also, the text describes alluvial fans as typically lacking very find material, but they can have overbank deposits within them (and the photo looks like it’s mostly fine material – ?).
p. 239 references Photo 7.1, but it should reference 7.17
Photo 7.21 is a bit dark
Figure 7.8 shows different kinds of valleys and log S-log A plots. The break between colluvial and bedrock valleys is shown around A = 10^5 m2. In the text (bottom of p. 228), the break is noted as occurring at A = 1-10 km2. First of all, perhaps the same units should be used. Second, a student trying to match the text to the figure will have difficulty as the area threshold described is not the same.
Photo for colluvial valley is quite dark.
Figure 7.6 shows a series of plots that should be log-log plots. On the velocity-Q plot, the numbers 1, 2, and 3 have become offset from their plotted points. Could you include a drainage basin with locations 1, 2, and 3 labeled on it?
Under “Sediment routing and Storage”, I really like the discussion of residence time. Bold it? Residence time is such an important concept. Is it defined elsewhere in the text?
There is a paragraph on p. 220 that describes the complexities of one type of hysteresis loop. There is a lot of the scatter in sediment rating curves isn’t related to hysteresis loops, but rather to changes in sediment supply over time. This is especially true for the washload component of suspended load. For ex., in agricultural areas, you can have different sediment rating curves for different seasons, depending on whether or not the crops are up. My suggestion would be to note that there is a lot of scatter in the sediment rating curves, cut out the discussion of hysteresis here (or mention it and link to figure 4.11 where it is well described), and then cut much of the next paragraph.
Instead, I would suggest bringing up the concept of sediment yield (mass/area) with the note that increasing basin area tends to decrease sediment yield as storage opportunities increase. This would follow on nicely after the notes on sediment accumulation rates measured at different scales.
The description of how to use a sediment rating curve to get sediment evacuation rates is missing a step. You accurately describe how to create a sediment rating curve, but to get sediment export, you would then have to apply it to the discharge record. That’s a different concept for students to get. Perhaps Fig. 7.3 could then show development of a sediment rating curve and then application to a hydrograph to get a sediment load.
Figure 7.2 The term ”Sediment yield” specifically refers to mass divided by area, but that’s not how it is being used here. Instead use the term “Sediment output” or “Sediment export” to represent the mass leaving the watershed. You might also change the middle photo of the alluvial fan. Yes, it is sediment storage, but it’s also at the mouth of a basin (as basins are often sketched on boards), and might be confusing. Do you have a picture of fresh deposition on a floodplain after a big flood?
figure 7.10 the boxes around each channel look un natural
Why do you reference some examples in the text (p.222 “Amazon River Basin, sediment storage”), but not show them in photographs or figures? This is very common in this chapter (and Chap 5). Are you trying to broaden the number of examples? It comes off as a disconnect – the photographs are commonly (not always) not the same examples as what is presented in the text
Photo 7.21 – poor quality photograph, dark, too much contrast, and not in focus – I get the feeling it is here to bolster your alluvial fan argument, and is not terribly representative
Fig 7.5 – the figure implies that the Strahler method is appropriate for stream length and Shreve for basin area comparisons. Why not present data from the two different schemes on the same graphs – showing how the measuring techniques affect resulting data?
Fig 7.1 – As a red-green colorblind guy, I have to struggle to see the drainage basin boundary on both parts of the figure Fig 7.5 – the arrow points at trees. I don’t find this photo very clear for what you are trying to say, Photo 7.13 does a better job (and is redundant in that aspect)
Box 7.1 – This uses “x” and “xd” interchangeably – looks like typos. Why not just use “x” or “xd” and define it?
Alluvial fans, p 238. I think you make the unnecessary and inappropriate distinction between “alluvial” and “debris” in the way you present your definitions. I get the feeling your distinction is based on the assessment of whether channels or debris flows dominate the exposed surfaces of the fans. I believe many of the fans have both (from my experience in the SW US)
Why drop in an example of “paraglacial’ here? (I’ve had managers get confused by this term, mixing it up with “periglacial”, why encourage confusion?). It seems out of place – use a fluvial example
I would have liked more explanation of salt lakes and how they form in this chapter. I also found the log scale vs the non-log scale graphs on page 221 confusing.I think that the implication should have been better stated. I also would have liked more clarification on transverse drainage and superposed. I also did not think that the river longitudinal profile equation helped my understanding of the chapter content.
Small detail but in figure 7.1 (218) arrows don’t match to the same features locations in the 2-dimensional and 3-dimensional views.
I believe that caption and Photograph. 7.8 tell a different story. I think the caption is wrong.
University of Vermont
Few more comments:
1. One thing that feels like it is missing from this chapter is any mention of deltas. Estuarine channels are mentioned, but not deltas. I would at least mention that they exist and note that they will show up in full force in ch. 8. It is hard to discuss sources and sinks of sediment without mentioning deltas.
2. There are a number of specific examples given (ex. p. 239: road cuts along White Mountains and Sierra Nevada; or terraces near the Grand Tetons) to illustrate points, but then there are not any photos of those sites. For readers unfamiliar with the locations, these points are not always helpful. If you want to refer to an iconic landscape, put in a picture that shows that iconic landscape with the geomorphic feature you are trying to explain. Or simply refer to them as “road cuts into fans near the base of active mountains” or “large valleys downstream from glaciated mountain ranges”, etc. Many students have never been out west, and actually seeing images of these landscapes in the context of what the geomorphology means might be more powerful.
3. Terraces. On p. 235, there is a line “For terraces to form, floodplain abandonment must be an episodic rather than gradual process.” is not technically true, as unpaired terraces can form due to lateral migration in the presence of overall downcutting. And on p. 237, this is noted at the end of the second paragraph.
4. Box 7.1 has a few issues. Dz/dx is not formatted properly in the equations, and it looks like x and xd are used interchangeably at times?
5. Overall, some of the figures use linear plots, some use log-log plots that are clearly labeled, and some use log-log plots but they are not labeled as such. I would go back and double-check them all to make sure that they are clearly labeled.
6. An earlier comment of mine pointed out the desire to have some verbage on the problem of sediment delivery in larger and larger watersheds, and ah ha! There is it in Digging Deeper. Thanks!
Few more figure comments:
Photo 7.7 notes that “The bar may eventually become vegetated and incorporated into the floodplain.” You could add the other possibility… or it may be remobilized during the next big flood and transported farther downstream.
Photo 7.9 is a bit washed out.
Photo 7.12b is pretty dark.
Photo 7.15 shows a strath terrace nicely. I don’t think Photo 7.14 is necessary.
Photo 7.16 – if you have a photo of a fill terrace that also shows the wide flat top of the terrace better, that would be good.
Photo 7.20 is too dark, making it hard to see the internal structure of the deposit. Also, the text describes alluvial fans as typically lacking very find material, but they can have overbank deposits within them (and the photo looks like it’s mostly fine material – ?).
p. 239 references Photo 7.1, but it should reference 7.17
Photo 7.21 is a bit dark
Figure 7.8 shows different kinds of valleys and log S-log A plots. The break between colluvial and bedrock valleys is shown around A = 10^5 m2. In the text (bottom of p. 228), the break is noted as occurring at A = 1-10 km2. First of all, perhaps the same units should be used. Second, a student trying to match the text to the figure will have difficulty as the area threshold described is not the same.
Photo for colluvial valley is quite dark.
Figure 7.6 shows a series of plots that should be log-log plots. On the velocity-Q plot, the numbers 1, 2, and 3 have become offset from their plotted points. Could you include a drainage basin with locations 1, 2, and 3 labeled on it?
Under “Sediment routing and Storage”, I really like the discussion of residence time. Bold it? Residence time is such an important concept. Is it defined elsewhere in the text?
There is a paragraph on p. 220 that describes the complexities of one type of hysteresis loop. There is a lot of the scatter in sediment rating curves isn’t related to hysteresis loops, but rather to changes in sediment supply over time. This is especially true for the washload component of suspended load. For ex., in agricultural areas, you can have different sediment rating curves for different seasons, depending on whether or not the crops are up. My suggestion would be to note that there is a lot of scatter in the sediment rating curves, cut out the discussion of hysteresis here (or mention it and link to figure 4.11 where it is well described), and then cut much of the next paragraph.
Instead, I would suggest bringing up the concept of sediment yield (mass/area) with the note that increasing basin area tends to decrease sediment yield as storage opportunities increase. This would follow on nicely after the notes on sediment accumulation rates measured at different scales.
The description of how to use a sediment rating curve to get sediment evacuation rates is missing a step. You accurately describe how to create a sediment rating curve, but to get sediment export, you would then have to apply it to the discharge record. That’s a different concept for students to get. Perhaps Fig. 7.3 could then show development of a sediment rating curve and then application to a hydrograph to get a sediment load.
Figure 7.2 The term ”Sediment yield” specifically refers to mass divided by area, but that’s not how it is being used here. Instead use the term “Sediment output” or “Sediment export” to represent the mass leaving the watershed. You might also change the middle photo of the alluvial fan. Yes, it is sediment storage, but it’s also at the mouth of a basin (as basins are often sketched on boards), and might be confusing. Do you have a picture of fresh deposition on a floodplain after a big flood?
figure 7.10 the boxes around each channel look un natural
Why do you reference some examples in the text (p.222 “Amazon River Basin, sediment storage”), but not show them in photographs or figures? This is very common in this chapter (and Chap 5). Are you trying to broaden the number of examples? It comes off as a disconnect – the photographs are commonly (not always) not the same examples as what is presented in the text
Photo 7.21 – poor quality photograph, dark, too much contrast, and not in focus – I get the feeling it is here to bolster your alluvial fan argument, and is not terribly representative
Fig 7.5 – the figure implies that the Strahler method is appropriate for stream length and Shreve for basin area comparisons. Why not present data from the two different schemes on the same graphs – showing how the measuring techniques affect resulting data?
Fig 7.1 – As a red-green colorblind guy, I have to struggle to see the drainage basin boundary on both parts of the figure Fig 7.5 – the arrow points at trees. I don’t find this photo very clear for what you are trying to say, Photo 7.13 does a better job (and is redundant in that aspect)
Box 7.1 – This uses “x” and “xd” interchangeably – looks like typos. Why not just use “x” or “xd” and define it?
Alluvial fans, p 238. I think you make the unnecessary and inappropriate distinction between “alluvial” and “debris” in the way you present your definitions. I get the feeling your distinction is based on the assessment of whether channels or debris flows dominate the exposed surfaces of the fans. I believe many of the fans have both (from my experience in the SW US)
Why drop in an example of “paraglacial’ here? (I’ve had managers get confused by this term, mixing it up with “periglacial”, why encourage confusion?). It seems out of place – use a fluvial example
I would have liked more explanation of salt lakes and how they form in this chapter. I also found the log scale vs the non-log scale graphs on page 221 confusing.I think that the implication should have been better stated. I also would have liked more clarification on transverse drainage and superposed. I also did not think that the river longitudinal profile equation helped my understanding of the chapter content.
Small detail but in figure 7.1 (218) arrows don’t match to the same features locations in the 2-dimensional and 3-dimensional views.
I believe that caption and Photograph. 7.8 tell a different story. I think the caption is wrong.