tomohawk creek report

GEOMORPHOLOGY

Tomahawk Creek Report

Fluvial Processes and Landforms –

Investigating Erosion and Deposition of a Meandering Stream

By: Andrew Barchak

UMKC

4/29/2014

INTRODUCTION

The Geomorphology class met to investigate the morphology and

discharge of Tomahawk Creek in Leawood, KS, to observe and collect data

relating to the fluvial geomorphic processes taking place. Measurements

obtained included determining the discharge and bankfull discharge regarding

cross-sections of the wetted channel, estimating the bedload using the belt line

transect method, and mapping the natural meander characteristics and mitigation

measures.

METHODS

To obtain the cross-section, members of the team measured the bankfull

width, and the vertical depths. With the tape measure stretched horizontally from

bank to bank (bankfull width), and another from the stretched tape down to the

surface of the ground or water (vertical depths), the vertical measurements were

taken in 1 meter intervals throughout the bankfull widths from the 3 different

cross sections. To obtain the wetted cross-section members of the team

measured the wetted width and reproduced a vertical measurement method as

described above only the depths were from the surface of the water down

vertically to the bottom of the streambed. The horizontal intervals were changed

from 1 meter as done on the bankfull widths to 1/10 of the total wetted width.

Velocity was also measured at each site, and using the float down method

a ball and a stopwatch were used and timed down the section. Members

measured out 10 meters and allowed the ball to float downstream. In Calculating

velocity, the average surface velocity (distance floated / average float time) is

found to get the m/s ratio.

Bedload was measured at the site as well. To obtain bedload data, group

members selected meander bends to designate a transect at the widest point of

the point bar towards the cutbank, and sampled pebbles in 1-meter by 1-meter

square and selected approximately 15 pebbles from the wetted and the dry point

bar. The pebbles were later measured for axis length and sorted by shape

ranging from very angular to angular to sub angular to sub rounded to rounded to

very rounded, which helps define the streams competence.

RESULTS AND DISCUSSION

The morphology of the stream suggests that it has typical characteristics

of a meandering stream, and the point bars and cutbanks are clearly visible and

directly adjacent to each other, and are followed by riffles and pools. The

elevation difference, although not measured, is obviously minor and attempts to

mitigate the erosional effects of the stream that have been put in place near C1

(refer to sketch map), and if not appropriately improved, will allow for further

direct erosion and also erosion downstream. Heavy rocks much larger than the

competence of the stream under normal conditions were positioned to reduce

any further erosion at C1, although these attempts have been unsuccessful as

most likely during the heavy rainfall events have destroyed the attempted

purpose as a new scarp is preceding it and further eroding the park. It also

appears that more rock will need to be placed directly across from the already

altered location to stop the opposite bank from being cut from underneath by the

stream as evidence by the riffles.

The discharge values calculated from the data collected are not equal at

each site along the stream: C1=1.65, C2=5.55, C3=1.94. Since there were no

tributaries along the section chosen for evaluation, the only possible explanations

are either infiltration or runoff somehow leading back into the stream, or the

incorrect measurement of either cross-sectional area or velocity. The discharge

calculations mentioned earlier were listed descending downstream. If the

proposed hypothesis of infiltration or runoff leading back to the stream were valid,

discharge values would be expected to increase downstream, this is not the case

as the C3 section decreased significantly over the first two sections. The second

hypothesis involving incorrect measurement is the most likely source of error. It is

also possible that the surface velocity is not an accurate measurement due to the

fact that it does not account for the differences that could occur in streambed

surface texture and shape.

Site C3 had the largest cross-sectional area but in contrast had the lowest

calculated discharge. Site C2 is most likely to flood due to its discharge being

nearly triple that of the largest section C3 but with only nearly 1/2 the bankfull

width, and compounded by a high velocity in C1 as well and a only slightly higher

channel width.

The competence of the stream during discharge conditions was similar for

C1 and C2, but much different for C3. The average size particle that could be

eroded for the sampled portion of the stream is .4mm, with the C1 and C2 cross

sections having .3mm and .1mm particle size contained in the transportation

threshold of the diagram, however the C3 section had a .8mm particle size

located in the deposition threshold of the diagram, most likely minimizing it

transfer ability. The maximum size particle that could be eroded for each of the

average velocities we measured would be .02 mm and the minimum size particle

would be .009mm, meaning these are rather small and possible testing error

comes into play.

CONCLUSION

Tomahawk Creek’s low velocity, discharge and mostly sub-angular to

angular bedload suggest that it is of low competence, and does not carry larger

particles very often or carry them from great distances. There is however a need

for mitigation as the park situated right next to the banks is continually being

eroded and danger for the loss of more park in the future. For future

investigations, knowledge of stream order and the reduction of errors by students

could prove to be more beneficial as groups would each have one task, and

compare notes. Then, on another visit sample the river using the same methods

with the groups changing task, and then compare and contrast each day to see if

human error can be minimized and depict a truer steam velocity, bedload, and

competence.

TABLES AND GRAPHS

BEDLOAD 1

Pebble # Powers Index A axis B axis C axis Zingg's C/B Zingg's B/A Type Krumbein's Index

1 Sub-angular 51.17 31.08 27.98 0.9002574 0.607387141 Sphere 0.692520492

2 Sub-rounded 56.02 44.78 14.8 0.33050469 0.799357372 Disc 0.595506535

3 Sub-rounded 47.52 38.74 16.86 0.435209086 0.81523569 Disc 0.661334898

4 Rounded 45.08 29.93 23.68 0.791179419 0.66393079 Rod 0.703893357

5 Sub-rounded 65.44 45.81 12.47 0.272211308 0.700030562 Disc 0.510951943

6 Sub-angular 64.55 43.25 27.88 0.644624277 0.670023238 Disc 0.661447627

7 Sub-angular 46.04 30.02 23.92 0.796802132 0.652041703 Rod 0.697108553

8 Sub-rounded 64.88 38.95 20.97 0.538382542 0.600339088 Blade 0.578932686

9 Sub-angular 73.19 65.69 24.82 0.377835287 0.897526985 Disc 0.672665543

10 Sub-angular 58.86 43.25 26.08 0.60300578 0.734794427 Disc 0.687940791

11 Sub-rounded 62.67 58.6 24.42 0.416723549 0.935056646 Disc 0.714235275

12 Sub-rounded 40.19 29.25 22.92 0.783589744 0.727792983 Sphere 0.745935868



15 Very angular 43.4 35 15.9 0.454285714 0.806451613 Disc 0.666032216

16 Sub-angular 78.6 44.7 20.9 0.467561521 0.56870229 Blade 0.532765678

17 Angular 45.4 38.7 13 0.335917313 0.852422907 Disc 0.624953259

18 Sub-rounded 38.6 37.4 25.8 0.689839572 0.968911917 Sphere 0.865178197

19 Sub-angular 44.2 30.2 11.3 0.374172185 0.683257919 Disc 0.559002327

20 Sub-rounded 51 25.7 14.1 0.548638132 0.503921569 Blade 0.518406726

21 Angular 69.3 33.8 20.2 0.597633136 0.487734488 Blade 0.521915907

22 Angular 37.3 36.4 16.2 0.445054945 0.975871314 Disc 0.751160793

38.47409091

BEDLOAD 2





4 Angular 55.57 42.34 32.72 0.772791686 0.7619219 Sphere 0.765528067

5 Sub-angular 38.57 32.76 16.57 0.505799756 0.849364791 Disc 0.714587982

6 Angular 60.8 39.83 17.31 0.434597037 0.655098684 Blade 0.571347159

7 Rounded 86.36 53.35 32.54 0.609934396 0.617762853 Blade 0.615142266

8 Angular 29.87 19.07 19.35 1.014682748 0.638433211 Rod 0.745052836

9 Angular 48.49 39.83 14.89 0.373838815 0.821406476 Disc 0.631829955


11 Angular 104.39 47.49 29.97 0.631080227 0.454928633 Blade 0.50736874

12 Sub-angular 84 41 21.7 0.529268293 0.488095238 Blade 0.501450813

13 Rounded 45.3 31.7 12.6 0.397476341 0.699779249 Disc 0.579532507

14 Sub-angular 43.4 35.4 13.7 0.38700565 0.815668203 Disc 0.636182117

15 Sub-angular 62 43.3 12.7 0.29330254 0.698387097 Disc 0.523001273

16 Sub-angular 44.9 38.7 14 0.361757106 0.861915367 Disc 0.645330373

17 Sub-rounded 63.8 44.3 17.8 0.401805869 0.694357367 Disc 0.57862091

18 Angular 57.1 24.6 24.5 0.995934959 0.430823117 Rod 0.569652042

19 Sub-rounded 62.7 32 21 0.65625 0.510366826 Blade 0.554980934

38.038421

BEDLOAD 3


1 Very angular 43.4 35 15.9 0.454285714 0.806451613 Disc 0.666032216

2 sub-angular 78.6 44.7 20.69 0.462863535 0.56870229 Blade 0.530975286

3 Angular 45.4 38.7 13 0.335917313 0.852422907 Disc 0.624953259

4 sub-rounded 38.6 37.4 25.8 0.689839572 0.968911917 Sphere 0.865178197

5 sub-angular 44.2 30.2 11.3 0.374172185 0.683257919 Disc 0.559002327

6 sub-rounded 51 25.7 14.1 0.548638132 0.503921569 Blade 0.518406726

7 Angular 69.3 33.8 20.2 0.597633136 0.487734488 Blade 0.521915907

8 Angular 37.3 36.4 16.2 0.445054945 0.975871314 Disc 0.751160793

9 sub-angular 84 41 21.7 0.529268293 0.488095238 Blade 0.501450813

10 Rounded 45.3 31.7 12.6 0.397476341 0.699779249 Disc 0.579532507

11 sub-angular 43.4 35.4 13.7 0.38700565 0.815668203 Disc 0.636182117

12 sub-angular 62 43.3 12.7 0.29330254 0.698387097 Disc 0.523001273

13 sub-angular 44.9 38.7 14 0.361757106 0.861915367 Disc 0.645330373

14 sub-rounded 63.8 44.3 17.8 0.401805869 0.694357367 Disc 0.57862091

15 Angular 57.1 24.6 24.5 0.995934959 0.430823117 Rod 0.569652042

16 sub-rounded 62.7 32 21 0.65625 0.510366826 Blade 0.554980934

35.8063

BEDLOAD 4


1 Sub-Angular 115.57 67.75 20.75 0.306273063 0.586224799 Blade 0.472148982

2 Sub-Angular 56.75 48.62 16.01 0.329288359 0.856740088 Disc 0.622909353

3 Angular 28.08 15.79 13.79 0.873337555 0.562321937 Rod 0.651204505

4 Angular 57.07 43.56 12.09 0.277548209 0.763273173 Disc 0.544794618

5 Very Angular 46.05 41.55 15.36 0.36967509 0.90228013 Disc 0.670143267

6 Angular 44.51 25.33 15.76 0.62218713 0.569085599 Blade 0.58626244

40.433333

BEDLOAD 5


1 sub-angular 77.49 62.32 26.5 0.425224647 0.804232804 Disc 0.650320332

2 Angular 54.38 23.3 15.8 0.678111588 0.428466348 Rod 0.499319125

3 Very angular 42.83 32.42 11.31 0.348858729 0.756946066 Disc 0.584691108

4 Rounded 34.55 27.27 9.39 0.344334433 0.789290883 Disc 0.598620441

5 Angular 69.85 35.36 16.81 0.475395928 0.506227631 Blade 0.495734392

6 Angular 88.91 48.98 24.59 0.50204165 0.550894163 Blade 0.534103425

7 sub-angular 57.16 38.82 13.79 0.355229263 0.679146256 Disc 0.547198778

8 sub-angular 51.05 28.32 19.5 0.688559322 0.554750245 Rod 0.596181903

9 sub-angular 55.38 42.76 19.52 0.456501403 0.772119899 Disc 0.648043067

10 Sub-rounded 39.96 33.11 12 0.362428269 0.828578579 Disc 0.628969842


12 sub-angular 42.65 34.42 17.25 0.501162115 0.807033998 Disc 0.688526455


14 Sub-rounded 94.7 65.51 20.74 0.316592887 0.691763464 Disc 0.53309605

15 Sub-rounded 43.82 34.57 18.51 0.535435349 0.788909174 Disc 0.693298644



18 Angular 60.12 42.71 15.16 0.354952002 0.710412508 Disc 0.563720216

19 sub-angular 47.36 35.07 18 0.513259196 0.740498311 Disc 0.655332381

20 Angular 65.4 50.45 27.11 0.537363726 0.771406728 Disc 0.683825141

21 sub-angular 58.17 42.24 26.88 0.636363636 0.726147499 Disc 0.694893659

22 sub-angular 44.27 35.08 21.7 0.618586089 0.79241021 Disc 0.729625647


24 Rounded 71.93 62.3 14.21 0.228089888 0.866119839 Disc 0.555163197

25 sub-angular 87.95 83.55 17.79 0.212926391 0.949971575 Disc 0.577054597

26 Sub-rounded 81.56 77.62 20.11 0.259082711 0.951692006 Disc 0.616799138

27 Angular 58.87 36.43 19.08 0.523744167 0.618821131 Blade 0.585351169

28 Angular 54.37 38.35 29.59 0.771577575 0.705352216 Sphere 0.726770386

29 sub-angular 88.33 65.11 19.68 0.302257718 0.737122156 Disc 0.547627745

30 sub-angular 62.05 55.86 14.06 0.25170068 0.900241741 Disc 0.588664112

31 sub-angular 64.58 70.6 13.23 0.187393768 1.093217714 Disc 0.607280712

32 Angular 54.07 31.06 17.06 0.549259498 0.57444054 Blade 0.565921134

33 Very angular 97.87 47.36 31.5 0.665118243 0.483907224 Blade 0.538031484

34 Angular 45.87 27.53 12.56 0.456229568 0.600174406 Blade 0.547746305

35 Angular 55.35 28.52 11.55 0.404978962 0.515266486 Blade 0.475516311


37 Very angular 87.67 42.9 31.02 0.723076923 0.489335006 Rod 0.557355585

38 Sub-rounded 69.2 56.35 31.76 0.563620231 0.814306358 Disc 0.720312152

39 sub-angular 58.26 39.73 8.17 0.205638057 0.681943014 Disc 0.457298616

40 sub-angular 39.91 40.72 11.65 0.286100196 1.020295665 Disc 0.667815887

41 sub-angular 39.82 37 12.39 0.334864865 0.929181316 Disc 0.661236532




45 Angular 68.12 39.83 15.18 0.381119759 0.584703464 Blade 0.506964559

46 sub-angular 65.99 52.28 18.84 0.360367253 0.792241249 Disc 0.609284421

47 Very angular 60.15 36.04 32.52 0.902330744 0.599168745 Rod 0.686785871

42.5481

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