Channel Evolution Model Overview

1. THE CHANNEL EVOLUTION MODEL (CEM), CHANNEL INCISION, FLOODPLAIN BENCHES,& CAN STREAMS REPAIR THEMSELVES?

2. Rented Track hoeDAVE DERRICK’S PERSONAL HEADCUT WORKING ITS WAY TOWARD HIS HOUSE. I spent 15 hrs straight on that machine!!

3. Channel Evolution Model (Schumm, et al. 1984) Originally developed to describe erosion evolution of Oaklimiter Creek, Calhoun City/Derma, MS.A location-time substitution conceptualization is used to generate a five-reach type incised channel evolution modelIn an idealized stream Types I-V will occur in sequence (series)

4. Channel Evolution Model Overview The primary value of the model is to determine the evolutionary state of the channel from a field reconnaissance. The evolution sequence provides an understanding that reaches of a stream may differ in appearance, but channel form in one reach is associated with other reaches by an evolving process. Form, process, and time relate dissimilar reaches of the stream. The CEM was originally designed to help understand a stream’s response to a downstream disturbance (typically bed lowering), although upstream disturbances are handled well too. From C. Watson

5. Channel Evolution Model

6. Channel Evolution Model Type I Reach Characteristics Type I reaches are generally characterized by a U-shaped cross section with little or no sediment stored in the channel bed. Type I reaches are located upstream of the actively degrading reach and have not yet experienced significant bed or bank instabilities. From C. Watson

7. < Type I is upstream of active incision

8. A dappled Dr. Watson in a CEM Type I stream

9. Stream connected with its floodplain, bed stable CEM Type I

10. Channel Evolution Model Type II Reach Characteristics Immediately downstream of Type I reaches, Type II reaches are encountered. Bed degradation is the dominant process in the Type II reach. Type II channels are steepened reaches where the sediment transport capacity exceeds the sediment supply. Although the channel is actively degrading in a Type II reach, the bank heights (h) have not exceeded the critical bank height (hc). Therefore, banks are not geotechnically unstable. From C. Watson

11. < Type II reaches are actively incising, although mass wasting of bank has not been initiated (h<hc)

12. A large knickpoint, Niagara Falls (American Falls) (This headcut moves on average 2.5 ft per year) Hard Dolomite overlaying weaker Rochester Shale, could result in a large riffle over time

13. Note large amount of stone at toe of falls Derrick 6-5-2009

14. So much rock fell that the Corps dewatered the American Falls in 1969 to see what was going on!! Derrick 6-5-2009

15. A headcut has to move upstream over time (toward the headwaters of the stream), if the waterfall does not move, it is not a headcut!!!

16. Headcut moving upstream on Johnson Cr, MS. CEM Type II

17. Typically knickpoints will not occur in non-cohesive materials (sands, etc.). Sand will not stand vertically with water flowing over it.

18. CEM Type II A series of small headcuts

19. Dr. Watson with large headcut in a CEM Type II stream, Johnson Creek, MS. Banks bad upstream

20. Looking US at a North Miss. stream, CEM Type II upstream (downcutting) & Type III (almost immediately twice as wide) in foreground.

21. Channel Evolution Model Type III Reach Characteristics As bed degradation continues, the bank heights and angles will continue to increase. When the bank heights have exceeded the critical bank height for stability, mass failures (geotechnical instability) begin to occur in the Type III reaches. The dominant process in the Type III reach is channel widening. From C. Watson

22. < In the Type III reach, mass wasting of the banks with rapid channel widening is the dominant process

23. CEM Type III, rapid over widening of stream

24. CEM Type III, banks fail, trees fall in

25. CEM Type III-bridges too short

26. CEM Type III Bellefontaine Creek, {sand & clay bed, rural, slope <1%} April 2005, rapid widening

27. Bellefontaine Creek about 700 ft US of the previous picture. CEM Type II, but the headcut is coming, followed by channel widening

28. HEADCUTS GONE BAD!!

29. Headword migration of knickpoints stopped by twin road culverts, north MS. A vehicle CEM Type III

30. Las Vegas Wash, NV. has degraded from a 1 ft deep by 100 ft wide channel in 1975, to a 40 ft deep by 1,000 ft wide channel in 1995!! Huge problems with perchlorate interception from the groundwater table I am standing on the roots of dead wetland plants, over 2,200 acres of wetlands lost

31. Then 2,400 Acres of Wetlands

32. Now 2000 acres of wetlands lost ! Photo by Gerry Hester

33. Channel Evolution Model Type IV Reach Characteristics The Type IV reaches are downstream of the Type III reaches and represent the first manifestation of the incised channel returning to a new state of dynamic equilibrium. In the Type IV reach, geotechnical bank instabilities and channel widening may continue, but at a much reduced rate. From C. Watson

34. < Channel widening continues at a much reduced rate in the Type IV reach. The first manifestation of a new equilibrium emerges.

35. CEM TYPE IV, North Miss. stream, overwidened, cannot process sediment

36. CEM Type IV, MS., should be a single-thread channel

37. CEM Type IV, Illinois

38. Channel Evolution Model Type V Reach Characteristics Type V reaches represent a state of dynamic equilibrium with a balance between sediment transport capacity and sediment supply. Bank heights in the Type V channel are generally less than the critical bank height, and therefore, geotechnical bank instabilities do not exist. From C. Watson

39. < Type V reaches represent a state of dynamic equilibrium with a balance between sediment supply and sediment transport capacity.

40. CEM Type III-IV-V

41. Old floodplain bench (hundreds of feet wide) is now a disconnected terrace CEM Type V, Middle Fork Worsham Cr. Duck Hill, MS New floodplain bench 6 ft wide

42. Long Creek, Batesville, MS, - CEM Type V stream, old floodplain (abandoned by stream), new floodplain bench CEM Type V

43. SO WHAT DOES THAT HAVE TO DO WITH ALISO CR. @ THE BEACH?? (Southern CA). IN MINUTES WE WILL SEE THE CEM TYPE 2 & 3 WORKING. Looking at Pacific Ocean wave action building a beach berm ALISO CREEK - PIX BY DERRICK 5-10-2009

44. Aliso Cr. had pooled up on the beach behind a low berm ocean waves had built. Stream has just broken through the berm & is flowing toward the Pacific Ocean ALISO CREEK - PIX BY DERRICK 5-10-2009

45. Two minutes later flow has increased. ALISO CREEK - PIX BY DERRICK 5-10-2009

46. Looking toward the ocean, in 3 minutes the channel went from CEM Type 2 (lowering) to Type 3 (widening). ALISO CREEK - PIX BY DERRICK 5-10-2009

47. The ponded water surface elevation dropped 39 inches in 10 minutes, kind of like a dam break. ALISO CREEK - PIX BY DERRICK 5-10-2009

48. A CEM QUICK QUIZ, LET’S THINK!!

49. Stream degradation?? Or local scour?? Air observed under the RDB highway bridge pier, Interstate 20, Clear Cr. Bovina, MS

50. Odd protection for LDB Interstate 20 bridge pier, left bank, Clear Creek, Bovina, MS, Air under protection.