Assessing Stream Channel Stability At Bridges in Physiographic Regions

 

3. FIELD OBSERVATIONS

Numerous stream-bridge intersections were observed across the United States to develop and test the stability assessment method. The streams were to reflect a broad range of stream types and physiographic regions; thus, 57 site visits were conducted in 13 physiographic regions and subregions, including Pacific Coastal, Basin and Range, Trans Pecos, southern Rocky Mountains, Great Plains, Central Lowlands, Interior Lowlands, Ozark-Ouachita Plateau, Appalachian Plateau, Valley and Ridge, Piedmont regions, and Atlantic Coastal Plain.

In addition to collecting observations at streams covering a variety of erosion issues, sizes, and physiographic regions, the following criteria also were used in selecting appropriate sites:

• All channels were alluvial or partially alluvial(occasional rock outcrops were acceptable).
• Engineered (straightened or widened) channels were included, although manmade canals were not.
• The streams had to be wade-able or partly wade-able.
• The streams and bridges had to be safely accessible.
• A reasonable level of personal physical safety had to be satisfied.
• The streams were located within a reasonable distance of the travel corridor.

The data for each of the streams are summarized in tables 5-7. Streams that are named N# in table 5 are unnamed on topographic maps. Table 5 provides the locations and global positioning system (GPS) coordinates of the bridges, the physiographic Province, land use, and stream classification. Each of the channels was classified according to the Montgomery-Buffington scheme. The Montgomery-Buffington scheme does not include engineered or altered channels. However, this method is still useful as a basic descriptor of the primary processes in the stream (e.g., transport versus response) and is, therefore, included. To include altered streams, the USACE method (10) and a simple observation of channel pattern (based on both field observation and aerial photos) also were used to classify or categorize the stream types. The resulting stream type is provided as a combination of these methods in table 5. The Rosgen classification method was not considered because it is unnecessarily data intensive for the purposes of assessing channel stability in the vicinity of a bridge. Table 6 provides the bed and bar material, the percent of sand (F_s), and any controls observed in the banks or on the bed. Table 7 provides observations made on the banks, including vegetation, bank material, bank height, and any erosion characteristics. In the next section, observations made in each of the physiographic regions are described.

*C = cascade, S = step pool, P = plane bed, R = pool-riffle, D = dune-ripple, B = braided, MT = mountain torrent, MA = meandering, MO = modified, S.R = State Route, Cr. = Creek, R. = River

Table 5. River data summary, continued.

River	Map Location	GPS Location		Physiographic Province	M-B/USACE Class*	Land Use	Channel Pattern
		N. Latitude (deg)	W. Longitude (deg)
12. Rt. 66 Wash	Rt. 66, E of Ludlow, CA	34.7160	116.1053	Basin and Range	B/AR	Natural	Arroyo/braided
13. Sacramento Wash	S.R. 68, 27.4 km E of Lauchlin, AZ	35.2250	114.2800	Basin and Range	R-B/MA-BR	Rural/mining	Meandering to braided
14. Rio San Jose	S.R. 6, 1.6 km S of I-40, Exit 126, NM	34.9675	107.1749	Trans Pecos	R/MA,MO	Grazed/natural	Meandering, channelized
15. Rio Puerco	S.R. 6, 24.2 km E of Los Lunas, NM	34.7966	106.9905	Trans Pecos	R/MA,MO	Grazed/natural	Meandering, channelized
16. W. Elk Cr.	E. Third St. (Rt. 66), W of Elk City, OK	35.4119	99.4522	Central Plains	R/MA,MO	Suburban, cattle	Meandering, channelized
17. Beaver Cr.	U.S. Rt. 183, ~1.6 km N of Arapahoe, OK	35.5941	98.9602	Central Plains	R/MA,MO	Agricultural, cattle	Meandering
18. Brush Creek	U.S. Rt. 62, 1.6 km E of Jacktown, OK	35.5068	96.9862	Central Plains	R/MA	Agricultural, grazed	Meandering
19. Unnamed	U.S. Rt. 62, 1.6 km E of Boley, OK	35.4862	96.4594	Central Plains	R/MA	Natural, grazed, rural	Meandering
20. Little Skin Cr.	U.S. Rt. 64, 1.6 km W of Muldrow, OK	35.3982	94.6211	Ozark-Ouachita Highlands	R/MA	Natural, rural	Meandering
21. Unnamed	U.S. Rt. 64, at Dyer, AR	35.4964	94.1363	Ozark-Ouachita Highlands	R/MA, MO	Rural	Meandering, straightened
22. Little Cypress Cr.	S.R. 59, 1.6 km S of I-40, Exit 35	35.3402	89.5018	Coastal Plain	R/MA	Agricultural, rural	Meandering

*C = cascade, S = step pool, P = plane bed, R = pool-riffle, D = dune-ripple, B = braided, MT = mountain torrent, MA = meandering, MO = modified, S.R = State Route, Cr. = Creek, R. = River

Table 5. River data summary, continued.

River	Map Location	GPS Location		Physiographic Province	M-B/USACE Class*	Land Use	Channel Pattern
		N. Latitude (deg)	W. Longitude (deg)
23. Unnamed	U.S. Rt. 70, 10.5 km W of Jackson, TN	35.6148	88.9909	Coastal Plain	R/MA	Agricultural, rural	Meandering
24. Unnamed	U.S. Rt. 79, 3.2 km SE of Milan, TN	35.8910	88.8105	Coastal Plain	R/MA	Agricultural, rural	Meandering
25. Honey Run	S.R. 76, 0.8 km E of White House, TN	36.4779	86.6397	Interior Low Plateau	P/MA	Rural	Slightly meandering
26. South Fork	S.R. 84 just NE of intersection with Rt. 357	37.5430	85.7685	Interior Low Plateau	P/MA	Agricultural, rural	Meandering
27. East Fork	S.R. 55 at intersection with U.S. Rt. 62, 3.2 km S of Bloomfield, KY	37.8816	85.3029	Interior Low Plateau	P/MA	Agricultural, rural	Meandering
28. Unnamed	U.S. Rt. 60 3.2 km E of I-40, Exit 101, ~ 9.7 km W of Sterling, KY	38.0443	83.9933	Interior Low Plateau	P/MA	Rural, grazed	Meandering
29. McKnown Cr.	U.S. Rt. 119 N at Robinson Rd., 2.4 km S of Walton, WV	38.5934	81.3792	Appalachian Plateau	P/MA	Rural	Meandering
30. Wolf Run	U.S. Rt. 199 N, 0.8 km S of Gandeville, WV	38.6896	81.3886	Appalachian Plateau	R/MA	Rural	Meandering
31. Alligator Cr.	S.R. 765, S of Punta Gorda, just S of US Rt. 41	26.8884	82.0213	Coastal Plain	D/MA	Suburban	Meandering
32. Peace R.	S.R. 70, 1.6 km W of Arcadia, Florida	27.2213	81.8766	Coastal Plain	D/MA	Suburban	Meandering

*C = cascade, S = step pool, P = plane bed, R = pool-riffle, D = dune-ripple, B = braided, MT = mountain torrent, MA = meandering, MO = modified, S.R = State Route, Cr. = Creek, R. = River

Table 5. River data summary.

River	Map Location	GPS Location		Physiographic Province	M-B/USACE Class*	Land Use	Channel Pattern
		N. Latitude (deg)	W. Longitude (deg)
33. Blackrock Run	Stringtown Road off S.R. 25, N of Butler, MD	39.5437	76.7331	Piedmont	R/MA	Suburban, agricultural, natural	Meandering
34. Indian Run	Benson Mill Rd, off S.R. 25, N of Butler, MD	39.5691	76.7445	Piedmont	R/MA	Natural, agricultural, rural	Meandering
35. Middle Patuxent R.	S.R. 108, N of Columbia, MD	39.2290	76.9173	Piedmont	R/MA	Natural, suburban	Meandering
36. Hammond Branch	Stephens Rd., 2.4 km N of Laurel, MD	39.1318	76.8449	Coastal Plain	R/MA	Suburban, agricultural	Meandering
37. Atherton Tributary	Seneca Dr., Columbia, MD	39.1871	76.8629	Piedmont	R/MA	Suburban	Meandering
38. Stocketts Run	Sands Rd., 4.8 km SW of Davidsonville, MD	38.8831	76.6638	Coastal Plain	R/MA	Natural, rural	Meandering
39. Mill Stream Branch	S.R. 213, just S of Centreville, MD	39.0401	76.0722	Coastal Plain	R6D/MA, MO	Agricultural, rural	Meandering
40. Kent County Tributary	S.R. 446 (Broadneck Rd.), SW of Chestertown, MD	39.2039	76.1235	Coastal Plain	R6D/MA	Agricultural	Meandering
41. Morgan Creek	Kennedyville Rd., 1.6 km E of Kennedyville, MD	39.2969	75.9845	Coastal Plain	D/MA	Agricultural	Meandering
42. Little Elk Cr.	Little Elk Rd, 1.2 km N of PA-MD line, 2.4 km S of Hickory Hill, PA	39.7271	75.9078	Piedmont	P6R/ MA	Agricultural, rural	Meandering

*C = cascade, S = step pool, P = plane bed, R = pool-riffle, D = dune-ripple, B = braided, MT = mountain torrent, MA = meandering, MO = modified, S.R = State Route, Cr. = Creek, R. = River

Table 5. River data summary.

River	Map Location	GPS Location		Physiographic Province	M-B/USACE Class*	Land Use	Channel Pattern
		N. Latitude (deg)	W. Longitude (deg)
43. Big Beaver Cr.	Kuntz Mill Rd., off U.S. Rt. 222, 6.4 km N of Quarryville, PA	39.9411	76.2204	Piedmont	R/MA	Agricultural	Meandering
45. Roaring Run	PA Rt. 445, E of Nittany, PA	40.9810	77.5442	Ridge and Valley	S/MT	Natural	Step-pool
44. Buffalo Run	Fillmore Rd. (S.R. 3008) near State College, PA	40.8595	77.8769	Ridge and Valley	P/MA, MO	Agricultural/ rural	Meandering/ straightened
46. Potter Run	S.R. 144 at Potters Mills, PA	40.8013	77.6257	Ridge and Valley	S/MT	Natural/rural	Step-pool to meandering
47. Bentley Cr.	S.R. 4013 (Berwick Turnpike), about 1.6 km S of Bentley Creek, PA	N/A	N/A	Glaciated Appalachian Plateau	R/MA, MO	Rural residential	Meandering to braided
48. N 48	S.R. 58, 1.6 km W of Allegheny R., PA, S of I-80,	41.1340	79.6944	Appalachian Plateau	P, M/MT	Natural/rural	Plane bed, meandering
49. Reids Run	S.R. 68, S of I-80 at Reidsburg, PA	41.1469	79.4020	Appalachian Plateau	P, M/MT	Natural, agricultural, rural	Plane bed, meandering
50. Piney Creek	S.R. 66, 0.8 km S of Limestone, PA	41.1281	79.3277	Appalachian Plateau	P, M	Rural, agricultural	Plane bed, meandering
51. Little Sandy Cr.	S.R. 3011 at East Branch Station, PA	41.0327	79.0509	Appalachian Plateau	P, M	Agricultural, rural	Meandering
52. Trout Run	S.R. 310, 1.6 km S of Reynoldsville, PA	41.0787	79.9016	Appalachian Plateau	P, M	Natural, agricultural, rural	Meandering

*C = cascade, S = step pool, P = plane bed, R = pool-riffle, D = dune-ripple, B = braided, MT = mountain torrent, MA = meandering, MO = modified, S.R = State Route, Cr. = Creek, R. = River

Table 5. River data summary, continued.

River	Map Location	GPS Location		Physiographic Province	M-B/USACE Class*	Land Use	Channel Pattern
		N. Latitude (deg)	W. Longitude (deg)
53. Pootatuck R.	Walnut Tree Hill Rd. near Sandy Hook, CT	41.4376	73.2702	New England	P-R, MA	Suburban, natural	Meandering
54. Mill R.	Judd Rd., N of Easton Reservoir, CT	41.3017	73.2760	New England	P, MA, MO	Natural	Meandering, straightened
55. Aspetuck R.	Silver Hill Rd. at Easton, CT	41.2596	73.3249	New England	P, MA, MO	Natural, rural	Meandering, straightened
56. W. Br. Saugatuck R.	Stonebridge Rd. at Wilton, CT	41.1949	73.3875	New England	P, MA	Natural, suburban	Meandering
57. Mianus R.	June Rd., N of Merritt Pkwy, Stamford, CT	41.1048	73.5867	New England	P, MO	Natural, suburban	Meandering, straightened

*C = cascade, S = step pool, P = plane bed, R = pool-riffle, D = dune-ripple, B = braided, MT = mountain torrent, MA = meandering, MO = modified, S.R = State Route, Cr. = Creek, R. = River

Table 6. River channel data.

River	w/y	Bed Controls	Bank Controls	Fs (%)	Bed Material	Bar Type	Bar Material	Bar Width	Bar Vegetation
1. Saline	20	None	Abutments	80	Sand	Alternate	Sand	1/2 W	Grasses
2. S. Fork Solomon R.	17	None	Abutments	100	Sand	Alternate	Sand	1/3 W	None/grass
3. N. Rush Cr.	15	None	None	80	Sand	None	None	N/A	N/A
4. Arkansas R.	14	Gravel and cobble armor	Boulders, gravel armor, bridge abutments	30	Cobbles	Point bars, midchannel	Very coarse gravel-cobbles	1/5 W	Minimal
5. Tomichi Cr.	19	None	Right bank riprapped	50	Very fine gravel	Midchannel (d/s only)	Unknown	< 1/5 W	Shrubs
6. Murietta Cr.	9	– None	None	100	Sand	Alternate	Sand	1/2 W	Heavily vegetated
7. Jacalitos Cr.	23	– None	Riprap at both bridge abutments	90	Sand	Irregular/ combo	Coarse sand	> 1/6, collectively very wide	Minimal
8. Dry Cr.	11	– Boulders and occasional bedrock	Occasional bedrock and abutments	10 u/s	Cobbles	None u/s; Alternate/ irregular d/s	Sand	1/2-2/3 W	None
9. Dutch Bill Cr.	10	– None u/s	Bridge abutments	50 u/s	Fine gravel	Point bars	Gravel	2/3 W	None
10. Buena Vista Cr.	7.5- 15	– None	None	100	Sand	Irregular	Sand	1/2 W	None
11. Mojave R.	6.7	– None	Piers, abutments	100 (fine)	Sand	Braided	Sand	Wide	None

Fs = portion of sand, u/s = upstream, d/s = downstream, W = width, R. = River, Cr. = Creek

Table 6. River channel data, continued.

River	w/y	Bed Controls	Bank Controls	Fs (%)	Bed Material	Bar Type	Bar Material	Bar Width	Bar Vegetation
12. Rt. 66 Wash	10	Boulders	Boulders, bridge protection, abutments	70	Sand, gravel	Irregular	Sand, gravel	Moderate	None
13. Sacramento Wash	20	None	Bridge protection, piers, abutments	75	Clay, silt, sand, gravel	Irregular	Sand and gravel	Moderate	None
14. Rio San Jose	5	None	Riprap, piers, abutments	70	Clay, silt, sand	None	N/A	N/A	N/A
15. Rio Puerco	16	None	Clay/silt cliffs, piers, bank stabilization	20	Silt, clay, sand	Alternate, point	Silt, clay	Wide	Grasses
16. W. Elk Cr.	9	Water line, debris	None	100 (silt)	Silt	None	N/A	N/A	N/A
17. Beaver Cr.	< 4	None	Bridge protection, soil blocks	100 (silt)	Clay, silt	Irregular	Clay/silt	Moderate	None
18. Brush Creek	5	Boulders from riprap	Bridge protection, bank stabilization	100 (silt, sand)	Clay, silt, sand	Irregular	Sand, silt, little gravel	None	Narrow
19. Unnamed	15	Boulders	Boulders, bridge protection, cliffs	100	Silt, sand	Irregular	Very fine sand	Wide	None, grasses

Fs = portion of sand, u/s = upstream, d/s = downstream, W = width, R. = River, Cr. = Creek

Table 6. River channel data, continued.

River	w/y	Bed Controls	Bank Controls	Fs (%)	Bed Material	Bar Type	Bar Material	Bar Width	Bar Vegetation
20. Little Skin Cr.	12	Beaver dams, debris	Bedrock, bridge protection	40	Sand, gravel	Alternate bars	Gravel	Grasses, shrubs	Moderate
21. Unnamed	5	Debris	Bars, debris	80	Silt, sand, gravel	Only under bridge	Sand	N/A	N/A
22. Little Cypress Cr.	9	Few boulders	Bridge abutments and pier	80	Sand w/ silt, gravel	Irregular	Sand	Narrow	None
23. Unnamed	9	Bridge protection	Debris, bridge protection	100	Sand	Irregular	Sand	Wide	None
24. Unnamed	9	Grade control	Bridge protection, piers	100	Sand	Irregular d/s only (u/s pooled)	Sand	Wide	None
25. Honey Run	12	Outcrop	Piers, bars	30	Gravel	Alternate	Gravel	Narrow	Grass/none
26. South Fork	9	None	Piers	30	Gravel	None	N/A	N/A	N/A
27. East Fork	9	Boulders, gravel armor	Bridge protection	50	Sand, gravel	None	N/A	N/A	N/A
28. Unnamed	12	Occasional bedrock, boulders	Occasional bedrock, abutments	20	Sand, gravel, cobbles	None	N/A	N/A	N/A
29. McKown Cr.	6	Gravel armor	Bridge protection	10	Gravel	None	N/A	N/A	N/A

Fs = portion of sand, u/s = upstream, d/s = downstream, W = width, R. = River, Cr. = Creek

Table 6. River channel data, continued.

River	w/y	Bed Controls	Bank Controls	Fs (%)	Bed Material	Bar Type	Bar Material	Bar Width	Bar Vegetation
30. Wolf Run	5-8	Gravel armor, occasional bedrock, grade control at bridge	Clumps of failed bank material	10	Gravel	Irregular (mostly from failure material)	Gravel	Moderate	None
31. Alligator Cr.	24	None	Confined left bank concrete wall or rock lined	18	Silt	None	N/A	N/A	N/A
32. Peace R.	20	– None	Gravel armor (bank protection), bridge riprap, debris	100	Very fine sand	Irregular/ combination	Very fine sand	Wide, 1/2 W	Grasses, reeds, trees
33. Blackrock Run	5.5-17	– Bedrock	Bedrock, abutments	65	Sand, gravel	Irregular	Sand, gravel	Narrow	None
34. Indian Run	5	Debris	Bridge riprap, abutments, fiber logs, debris	50	Sand, gravel, cobbles	Irregular	Sand, gravel	Wide	Grasses
35. Middle Patuxent R.	16	Gravel armor	Bedrock, gabions, riprap at bridge	20	Sand, gravel	Mid, point	Sand, gravel	Narrow	None
36. Hammond Branch	7	Boulders	Bridge protection, abutments, riprap	60	Sand, gravel	None	N/A	N/A	N/A

Fs = portion of sand, u/s = upstream, d/s = downstream, W = width, R. = River, Cr. = Creek

Table 6. River channel data, continued.

River	w/y	Bed Controls	Bank Controls	Fs (%)	Bed Material	Bar Type	Bar Material	Bar Width	Bar Vegetation
37. Atherton Tributary	16	Bedrock, boulders	Boulders, abutments	40	Sand, gravel, boulders	Irregular	Sand	Narrow	None
38. Stocketts Run	16	None	Abutments	50	Sand, gravel	Point	Sand, gravel	Moderate	None
39. Mill Stream Branch	13-16	None	Abutments, debris	100	Sand	Alternate	Sand	Narrow	None
40. Kent County Tributary	3	None	Abutments, concrete slabs	80	Silt, sand, gravel	Irregular	Silt, sand	Wide	Grasses
41. Morgan Cr.	10	None	Riprap, abutments	80	Silt, sand	None	N/A	N/A	N/A
42. Little Elk Cr.	20	Boulders	Bedrock, boulders, bridge protection, abutments	20	Sand, gravel, cobbles, boulders	Point	Gravel, cobbles	Narrow	None/grasses
43. Big Beaver Cr.	20-29	Gravel armor (d/s)	None	20	Silt, sand, gravel, cobbles	Midchannel (u/s), point (d/s)	Silt (u/s), sand, gravel (d/s)	Wide	None
44. Buffalo Run	10	Gravel armor, u/s weir	Bridge protection	30	Sand, gravel	None	N/A	N/A	N/A
45. Roaring Run	20	Boulders, riprap from failed bridge protection	Bridge protection, bank stabilization	10	Gravel, cobbles, boulders	Alternate (d/s only; u/s step-pool)	Gravel, cobbles	Moderate	None

Fs = portion of sand, u/s = upstream, d/s = downstream, W = width, R. = River, Cr. = Creek

Table 6. River channel data, continued.

River	w/y	Bed Controls	Bank Controls	Fs (%)	Bed Material	Bar Type	Bar Material	Bar Width	Bar Vegetation
46. Potter Run	15	Gravel/cobble armor	Bridge abutments, bank stabilization	30	Sand, gravel, cobbles	None	N/A	N/A	N/A
47. Bentley Cr.	32	None	Abutments	60	Gravel	Point, midchannel	Gravel	1/4-2/3 W	None
48. N 48	15	Gravel/cobble armor	Boulders, abutments, bank stabilization	10	Gravel, cobbles	None	N/A	N/A	N/A
49. Reids Run	15	Gravel/cobble armor, boulders	Boulders, abutments	10	Gravel, cobbles, boulders	None	N/A	N/A	N/A
50. Piney Creek	10	Gravel armor	Bridge protection, abutments, bank stabilization	< 20	Gravel, cobbles	Point bar	Gravel	Moderate	None
51. Little Sandy Creek	18	Gravel armor	Abutments	< 20	Gravel, cobbles, boulders	Midchannel	Gravel	Grasses	Narrow
52. Trout Run	10	Gravel armor	Bridge protection, abutments	30	Gravel, cobbles	None	N/A	N/A	N/A
53. Pootatuck R.	28	Bedrock, boulders, gravel armor	Boulders, abutments	10	Gravel, cobbles, boulders	Irregular	Gravel, cobbles	Narrow	None

Fs = portion of sand, u/s = upstream, d/s = downstream, W = width, R. = River, Cr. = Creek

Table 6. River channel data, continued.

River	w/y	Bed Controls	Bank Controls	Fs (%)	Bed Material	Bar Type	Bar Material	Bar Width	Bar Vegetation
54. Mill R.	13	Gravel armor, beaver dam d/s	Abutments	50	Sand, gravel	Alternate d/s	Sand, gravel	Narrow	None
55. Aspetuck R.	19	Gravel riffles	Boulders, bridge protection, bank stabilization	60	Sand, gravel	Alternate d/s (minor)	Sand	Narrow	None
56. W. Br. Saugatuck R.	45	Boulders	Boulders, abutments, debris jams, islands	40	Sand, gravel, cobbles	Midchannel, islands	Sand, gravel, cobbles	Moderate	Shrubs, trees
57. Mianus R.	13	Gravel armor (d/s of dam)	Boulders, abutments, bank stabilization	40	Gravel, cobbles	None	N/A	N/A	N/A

Fs = portion of sand, u/s = upstream, d/s = downstream, W = width, R. = River, Cr. = Creek

Table 7. River bank data.

River	Material	Bank Angle (deg)	Bank Height (m)	Vegetation	Erosion Location	Bank Failure Locations	Exposed or Bare Banks
1. Saline R.	Silty clay loam	30-60	0.9	Grass, deciduous trees; single dense and continuous band; healthy, vertically oriented	None	None	Minimal
2. S. Fork Solomon R.	Sand	30-60	0.6	Grass, reeds; no trees on channel banks; but in flood plain	Opposite and behind bars; adjacent to structures	No mass wasting	Frequent, but no cohesion
3. N. Rush Cr.	Loam/sand	60-80	0.9	Grasses	General fluvial; outside meander bends	Outside meanders	Outside meanders high, vertical
4. Arkansas R.	Sand, gravel, cobbles, silt	30-60	1.8	Grass, shrubs, deciduous and coniferous trees, healthy, vertical	Along straight reaches	Minor	Minor
5. Tomichi Cr.	Silty clay	Vertical	0.9	Grass, few deciduous trees (riparian, not bank)	Minor	None	None
6. Murietta Cr.	Sandy silty clay	60-80	1.5-2.4	Reeds, sparse deciduous trees well back from bank in flood plain, vertical	General, along channel banks	General; bank slides visible	Frequent, but sand so collapse
7. Jacalitos Cr.	Sand, gravel	30-60 (Vertical at outside bends)	0.9	Grass, deciduous trees	General fluvial, outside meanders	Outside meanders, recent slides	Occasional
8. Dry Cr.	Silty clay	Vertical	0.6-4.6	Dense deciduous trees; healthy, diverse, some leaning 30E	Outside meander; upstream of structure	General where too steep	Minor
9. Dutch Bill Cr.	Silt	Vertical	0.9-6.1 (incised)	Deciduous trees, some in channel (lateral migration)	Fluvial outside meander	Minimal	Some u/s of right abutment

LB = left bank, RB = right bank, u/s = upstream, d/s = downstream, R. = River, Cr. = Creek

Table 7. River bank data, continued.

River	Material	Bank Angle (deg)	Bank Height (m)	Vegetation	Erosion Location	Bank Failure Locations	Exposed or Bare Banks
10. Buena VistaCr.	Sand/silt	60-90	0.6	Sparse shrubs	General, irregular	Slides in sand	Frequent
11. Mojave R.	Sand	60-90	1.8	None	General	Continual slides	Continual
12. Rt. 66 Wash	Clay, silt, sand	70-90	0.6-1.8	None	General	Frequent	Continual
13. Sacramento Wash	Clay, silt, sand, gravel	60-90	0.9	Few shrubs	General	Frequent slides, slumps	Continual
14. Rio San Jose	Clay, silt, sand	60-90	1.8	Desert shrubs	Outside meanders, general	Outside meanders	Continual
15. Rio Puerco	Clay, silt	80-90	1.5	Grasses, shrubs (desert)	Outside meanders, general	Outside meanders	Continual
16. W. Elk Cr.	Clay, silt	70-90	1.5	Grasses, shrubs, few trees	General	Where hoof damage, steep banks	Continual
17. Beaver Cr.	Silt	90	2.4	Grasses, few bushes	General	Both banks-overheightened	Continual
18. Brush Creek	Silt	80	1.2-9.1 (top)	Sparse trees	General	Minor, both banks	Continual
19. Unnamed	Clay, silt, sand	40-60	1.2-4.6	Sparse trees, grass, shrubs	Outside meander bends	RB	Frequent
20. Little Skin Cr.	Clay, silt	60	1.5	Grass, shrubs, trees (moderately dense)	Outside meander bend, general	Mostly d/s	Occasional

LB = left bank, RB = right bank, u/s = upstream, d/s = downstream, R. = River, Cr. = Creek

Table 7. River bank data, continued.

River	Material	Bank Angle (deg)	Bank Height (m)	Vegetation	Erosion Location	Bank Failure Locations	Exposed or Bare Banks
21. Unnamed	Clay, silt (main), sand	70-90	0.9	Grass, shrubs, dense trees	General	None	Minor
22. Little Cypress Cr.	Clay, silt	90	0.9-3.7	Grass, dense trees	General	Outside bend	Continuous
23. Unnamed	Clay, silt, sand	80	2.4	Grass, dense trees	General, outside bends	General-overheightened banks	Frequent
24. Unnamed	Clay, silt	60-70	4.6 (levee)	Grass, dense trees	General	None	Occasional
25. Honey Run	Clay, silt	60-90	0.9-1.8 (top of mass wasting)	Grass, dense trees	General	Along RB, especially where vegetation removed	Occasional
26. South Fork	Clay, silt	70-80	2.4	Shrubs, sparse trees	General	Along both banks	Frequent
27. East Fork	Clay, silt	70	1.2	Grass	Outside bend, general	None	Occasional
28. Unnamed	Clay, silt	60-90	0.8	Shrubs, dense trees	General (minor u/s)	None	Occasional
29. McKown Cr.	Clay, silt	60-90	1.2 (u/s), 0.8 (d/s)	Grass u/s, d/s grass on left bank, one row of trees on right	General	U/s only along banks	Occasional
30. Wolf Run	Clay, silt, gravel	60-90	1.2	Grass	General, outside, inside bends	Both banks	Frequent
31. Alligator Cr.	Silt, sand	LB vertical, RB moderate	0.8	LB grass, RB dense trees	LB none (concrete), RB outside meander bend (minor)	None	None

LB = left bank, RB = right bank, u/s = upstream, d/s = downstream, R. = River, Cr. = Creek

Table 7. River bank data, continued.

River	Material	Bank Angle (deg)	Bank Height (m)	Vegetation	Erosion Location	Bank Failure Locations	Exposed or Bare Banks
32. Peace R.	Sand	Steep outside bend, moderate elsewhere	3	Dense trees	Opposite bar, outside meander bends	Left bank, outside bends	Minor both banks
33. Blackrock Run	Clay, silt, sand	50-80	0.9-2.7	Shrubs, trees	Outside meander, opposite bar	General-overheightened banks	Occasional
34. Indian Run	Clay, silt	40-80	0.8-1.8	Sparse trees LB, grass RB	General, opposite obstructions	RB where no vegetation	Occasional
35. Middle Patuxent R.	Clay, silt	40-60	1.5-1.8	Shrubs, dense trees in good condition	Outside meander bends, general	Limited on RB where high banks slough	Frequent on both banks
36. Hammond Branch	Clay, silt	60-80	1.5	Grasses, sparse trees, falling into stream, poor condition	Outside meander, general	Minor	Continuous
37. Atherton Tributary	Clay, silt	60-80	2.5-6	Sparse trees LB, dense trees RB, falling trees both banks	Outside meander	None u/s, RB d/s where trees removed	Occasional
38. Stocketts Run	Clay, silt	30-50, 80-90 outside bends	0.8-1.8	Shrubs, dense trees, falling on either side	Outside meander, general	None	Frequent
39. Mill Stream Branch	Clay, silt	40-60	0.9-2.4	Sparse falling trees LB, dense falling trees RB	General	None	Occasional

LB = left bank, RB = right bank, u/s = upstream, d/s = downstream, R. = River, Cr. = Creek

Table 7. River bank data, continued.

River	Material	Bank Angle (deg)	Bank Height (m)	Vegetation	Erosion Location	Bank Failure Locations	Exposed or Bare Banks
40. Kent Co. Tributary	Clay (minor gravel toward bottom)	30-80 (lower where bank failed)	2.4	Grasses, sparse falling trees	General	Both banks, continuous	Frequent
41. Morgan Cr.	Clay, silt	30-80, ragged	0.9	Shrubs, sparse trees, trees upright on both banks	General, ragged, irregular banks	Minor	Continuous
42. Little Elk Cr.	Clay, silt, sand	25-34	0.8-0.9	Shrubs, trees, trees upright in good shape	Outside meander bend	None	Occasional
43. Big Beaver Cr.	Clay, silt, sand	Vertical u/s, 30-40 d/s	1.2-2.1 (highly variable)	Grasses u/s, trees beyond 122 m u/s	Outside meander, opposite bar/obstruction	Both banks everywhere for 122 m u/s	Continuous
44. Buffalo Run	Clay, silt	Steep	0.8	Grass, shrubs	General fluvial	RB (ragged)	Frequent on right
45. Roaring Run	Clay, silt, cobbles, boulders	Steep	0.8 (cliff on left)	Rhododendron, trees upright, good shape	Outside meander bend	None	Rare
46. Potter Run	Clay, silt	Moderate to steep	0.6	Trees in good shape on left, grass on right	General fluvial on right	RB along grass	Where grass only
47. Bentley Cr.	Silt, sand, gravel	70-90	0.9	Grass, few trees	General fluvial	Minimal	Frequent
48. N 48	Clay, silt	Moderate to steep	0.6	Very dense trees, healthy, minor grass	General, outside meander bend	None	Minor along reach

LB = left bank, RB = right bank, u/s = upstream, d/s = downstream, R. = River, Cr. = Creek

Table 7. River bank data, continued.

River	Material	Bank Angle (deg)	Bank Height (m)	Vegetation	Erosion Location	Bank Failure Locations	Exposed or Bare Banks
49. Reids Run	Clay, silt, cobbles	Moderate to steep	0.9	Moderately dense healthy trees; grasses and shrubs	General	None	Minor along reach
50. Piney Cr.	Clay, silt, sand, gravel	Moderate to steep	1.1	RB grass only; LB healthy trees and shrubs	General	Minor on RB	Minor
51. Little Sandy Cr.	Clay, silt	Moderate	0.8	Grass within 152.5 m u/s of bridge; further u/s healthy dense trees	General	Along grassy areas	Moderate under tree roots and along grass
52. Trout Run	Clay, silt	Steep	0.9	Very dense shrubs, dense healthy trees	General, minor	None	None
53. Pootatuck R.	Clay, silt, sand, gravel, cobbles	Moderate	0.8	Trees, leaning on RB, good shape otherwise	Minor general fluvial	Some mass wasting where trees removed	Occasional
54. Mill R.	Silt, sand, gravel	Steep	0.6	Grasses, annuals, trees. Trees leaning slightly, sparse on LB, dense on RB, good shape	General fluvial	None	Occasional
55. Aspetuck R.	Clay, silt, sand	Moderate	1.1	Annuals (ferns), trees. Moderate density in good shape	General fluvial	None	Occasional
56. W. Br. Saugatuck R.	Clay, silt, sand, gravel	Moderate	0.8	Annuals, shrubs, trees in good health	General fluvial, opposite obstructions (significant)	None	Occasional
57. Mianus R.	Clay, silt, sand, gravel	Moderate to steep	0.9	Annuals, shrubs, trees moderately dense in good shape	General fluvial	None	Minor

LB = left bank, RB = right bank, u/s = upstream, d/s = downstream, R. = River, Cr. = Creek

PHYSIOGRAPHIC REGIONAL OBSERVATIONS

Thirteen physiographic regions and subregions were included in the data set. A wide variety of land uses were observed in the various regions, including natural, agricultural, grazed, rural, and suburban. Width-to-depth ratios also varied widely, from 5 to 24. As expected, the largest ratios were associated with braided or semibraided channels. Very low width-to-depth ratios were associated with incised streams or those that had been engineered. Bed materials varied from very fine materials (silt and very fine sand) in the Midwest and coastal areas to coarser materials mostly associated with higher elevation streams. Bank materials varied widely. For example, the banks of the streams in the Central Plains tend to be made up of fine loess and silt deposits, which erode easily. In the Appalachian Plateau region, in contrast, the bank materials are far more cohesive and tend to be less susceptible to high erosion rates even when bank vegetation was limited.

Although stream types vary widely within any of the physiographic regions, certain common characteristics were observed. A general summary of those observations is given here. The photos of the sites are organized by physiographic region in appendix A. Many, but not all, of them are referred to in the discussion below.

Pacific Coastal

There are two striking features of stream channels within the border and lower Californian subregions of the Pacific Coastal region (see appendix A). The first is the wide diversity in types of channels. Streams range from perennial, cascading channels to arroyos. The second feature common to most streams in these subregions is the frequency of human interference and alteration. The channel bed material in most of the streams (other than first-order streams) was predominantly fine-to-medium sand, while the channel banks were sandy. The average width-to-depth ratio was 12.1. The streams tend to be very high energy; they are typically ephemeral, so they carry water only when there is rainfall. Many of these streams (and arroyos) tend to be naturally unstable, particularly in the lateral direction, and have relatively high width-to-depth ratios. Because of the high degree of channel instability and flash flooding in this region, many, if not most, of the channels in suburban to urban settings were either concrete lined or at least heavily armored with rock. Channels in the outlying areas were unlined.

Intermontane

Observations at bridge-stream intersections were collected in the Basin and Range, Colorado Plateau, and Trans Pecos subregions within the Intermontane physiographic region. Many channels within the Colorado Plateau are bedrock or semialluvial channels in which stability is a function of bedrock erosion. In the Basin and Range, however, where the climate is arid to semiarid over much of the area, the streams are ephemeral with high energy, flashy flows (see appendix A). The energy of these streams combined with the highly erosion-prone sand beds and banks creates unstable channels, particularly at bridges. Due to the high sediment load carried by these streams, the width-to-depth ratios are relatively high, with an average of 25.0. Streams in the Trans Pecos region (see appendix A) tend to have high, steep banks or valley walls, which create valley side failures and subsequent failure material to the stream. The bed materials are sand, and banks are comprised of a mix of noncohesive materials, primarily sand, with minor amounts of cohesive silts and clays. The predominant bank vegetation was desert shrubs, and mass wasting was a common form of erosion. The average width-to-depth ratio was 10.5.

Rocky Mountain System

The southern Rocky Mountains were visited in this region (see appendix A). The channels contain large bed and bank material. The streams tend to be stable, transport streams that are less disturbed by human activities than in other physiographic regions. Stream channel banks are a mix of cohesive silts and clays and noncohesive gravels and larger materials. The average width-to-depth ratio was 16.5.

Interior Plains

Three subregions-the Great Plains, Central Lowlands, and Interior Lowlands-were visited within the Interior Plains. In the Great Plains (see appendix A), vegetation in riparian areas and in the flood plains was thick, lush, and dense, except where cattle were permitted to graze. The channel beds were composed of more than 70 percent sand. Bank material was noncohesive silt, loam, and sand, but the thick vegetation helped to keep banks stable. The average width-to-depth ratio was 17.3. Erosion processes within the stream channels are primarily fluvial; observed channel banks were not sufficiently high to create significant mass wasting. Slow to moderate degradation occurred where cattle grazing was permitted.

The Central Lowlands (see appendix A) had silt and loess banks that eroded easily. Many of the streams observed had been straightened in addition to having extensive hoof and/or grazing damage. The channel beds degrade rapidly since the bed material is predominantly silt with some clay and sand. The silt banks then become overheightened, and mass failures result. High, failing banks were common even where a wider riparian buffer existed, but the rate of failure was slower (for example, see figure 7). The average width-to-depth ratio was much lower than that observed in the Great Plains, with an average of 8.3. This may be due in part to channel modifications, such as straightening.

Streams in the Interior Lowlands (see appendix A) seemed less fragile than those in the Central Lowlands due to larger bed material (sand and gravel) and more cohesive materials in their banks (clay and silt). However, where vegetation had been removed, banks failed even when they were not greatly overheightened (see figure 8). A single row of trees in the riparian areas slowed bank failure dramatically. These streams tend to have a low width-to-depth ratio, with an average of about 10.5, and remain stable even when the surrounding land has been disturbed. This may be due to the existence of rock outcrops in the beds and banks.

Interior Highlands

In the combined Ozark-Ouachita Plateau (see appendix A), bed material was larger, containing some gravel. The bank material contains a significant percentage of cohesive clays. Natural erosion occurred at bends with increased mass wasting at bends where vegetation had been removed. Overheightened banks remained stable when more than one row of trees was in place. The average width-to-depth ratio was 8.5.

Appalachian Highlands

Within the Appalachian Highlands, the Appalachian Plateau, Valley and Ridge, and Piedmont regions were visited. In the Appalachian Plateau (see appendix A), bed material was coarser (mainly very coarse gravel to cobbles), with bank material composed of cohesive clay, silt, and minor sand. Critical bank heights appeared to be about 1.5 to 1.8 m, which result in low width-to-depth ratios. For the sites visited, the average ratio was 11.0. Watersheds are heavily forested where vegetation is undisturbed. Stream channel erosion and destabilization occurs through removal of vegetation and/or channel straightening. Overheightened banks may fail, but heal quickly if vegetation is allowed to re-establish; thus, stability tends to be fair at worst.

Stream channels within the Piedmont region (see appendix A) had cohesive banks that could stand at high angles without failure. Bank vegetation, if undisturbed, was dense and provided bank stability with about one river width of woody vegetation. Banks with angles steeper than about 60E tended to have leaning or fallen trees. The potential for debris jams is high. Occasional bedrock outcropping was noted at all streams that were visited. Bed material was sand and gravel with occasional larger material. The average width-to-depth ratio was 15.3.

The Valley and Ridge region of the Appalachian Highlands is comprised of a series of ridges separated by stream valleys. The streams in this region are often very steep, especially coming down from the ridges (see appendix A). Cascade and step-pool morphologies are common. Thus, bed materials are commonly large, such as cobbles and boulders, and often armor the bed. Banks are cohesive clays and silts with some larger materials mixed in, strongly held together by the lush vegetation found in this area. Disturbance to the banks by removal of vegetation may result in ragged, scalloped banks, but erosion of the banks is typically at a relatively slow rate. The average width-to-depth ratio was 15.0.

Figure 7. Failing banks in the Central Lowlands.

Figure 8. Failing banks in the Interior Lowlands.

Coastal Plain

The Coastal Plain covers a very large area of the Atlantic and Gulf coastal areas (see figure 6). Sites were visited along both the Atlantic and Gulf coasts (see appendix A). In both of these areas, researchers observed moderate rates of bed degradation and bank failure. A buffer of at least one river width appeared to be sufficient in most locations to keep banks stable. Where undisturbed, lush vegetation on the banks held the banks in place, resulting in excellent stability, even when banks were nearly vertical. Bed material is typically sand with minor amounts of small gravel, and banks are cohesive with clay, silt, and minor amounts of sand. Because of the cohesive banks, strong vegetative resistance, and degradation, width-to-depth ratios tended to be rather low. Streams in this region are often sluggish due to low slopes and backwater from the bays or estuaries into which they flow. Where banks or the flood plain are disturbed, debris jams are frequent. The average width-to-depth ratios were much lower in the Gulf area (9.0) than in the Atlantic area (13.5).

New England

All of the streams visited in the New England region were located in Connecticut. At all streams, the banks were heavily vegetated with large woody vegetation, providing tremendous stability to the streambanks. The bank materials typically were comprised of some cohesive materials combined with silt, sand and, in some places, gravel and larger particles. The bed materials in the New England region are considerably larger than in the Atlantic Coastal Plain to the south. The sand, gravel, and cobble beds were often armored; the width-to-depth ratios reflected this armored condition with an average value of 24. The channels were all meandering, but with beds transitional between plane beds and pool-riffle beds.

General Observations of Streams at Bridges

Channel stability is a function of levels of disturbance to the water and sediment discharges, and susceptibility of the channels to change. In every physiographic region, the disturbance that caused the greatest damage to the streams was the combination of cattle activity, vegetation removal, and channel straightening. The combined impact of these activities was worst where cattle had direct access to streams. Also, susceptibility of the channel banks to erosion significantly impacted the level of damage. Figures 9 and 10 provide examples of this combination of disturbances. All vegetation has been removed either through farming practices or by cattle grazing. The channel apparently had been straightened to provide better drainage and to maximize land for farming. Not only are cattle grazing in this area, but also they have direct access to the stream. Hoof damage is extensive. The combined disturbances have resulted in stream channel destabilization; the channel bed elevation has degraded and the banks have become overheightened and steepened. Figure 10 shows the eroding channel beneath the single-span bridge.

In many cases, maintaining a riparian buffer of an appropriate width is all that is needed to preserve channel stability. As discussed in the descriptions of the streams channels across the physiographic regions, some regions require only a single row of trees to help maintain stability, while others require a much greater width. This is due to bank materials and the susceptibility of the banks to failure. In the cases where channels are degrading because of channel straightening, cattle grazing, and urbanization effects, a vegetation buffer may not be enough to maintain stability. When the channel degrades, banks can become overheightened and fail through mass wasting. In this case, vegetation may help to slow the rate of failure, but usually cannot prevent collapse of the banks.

Figure 9. Stream impacts due to disturbances, including hoof damage,
vegetation removal, and channel straightening.

Figure 10. Impacts of disturbances at bridge (from figure 9).

Another observation that was frequently made at sites in all physiographic regions was that there was often a distinct change in channel stability upstream and downstream of the bridges. This was caused in every case by a change in property management, as it is common for a road (and, thus, a bridge) to divide property ownership. As an example, unnamed stream N 28 is wooded upstream, with a healthy wide band of upright trees keeping the banks stable (see figure 11). Immediately downstream of the bridge, all trees and other vegetation have been removed, resulting in destabilization of the banks (see figure 12).

Aerial photos were examined for each of the sites using http://terraserver-usa.com (these photos are not included in the report because they are readily available online). The photos were examined to check a larger view of the river, specifically looking at land use in the watershed and flood plain, construction areas, the extent of the riparian buffer, channel straightening, and channel pattern. In most cases, the aerial photos reinforced observations that were made on the ground. In a number of cases, the photos helped put the bridge reach into the perspective of the meander pattern, particularly where the bridge was located between meanders or just downstream of a tight meander. Old abandoned meanders also could be detected sometimes, giving an indication of previous lateral movement. Changes in channel pattern, for example from meandering to braided, can be detected on aerial photos. Examining the photos before or after visiting a site helped provide a rating, especially for the watershed condition factor.

Figure 11. Wooded land upstream of bridge.

Figure 12. Downstream of figure 11, vegetation removed.

EFFECT OF CHANNEL INSTABILITY ON BRIDGES

Unstable channels can cause a variety of problems at bridges; however, this is not necessarily the case. For example, the Mojave River in California (see figure 13) can be considered to be a naturally unstable channel, primarily in the lateral direction, in that there is considerable lateral movement of the channel. The channel bed and banks are noncohesive fine sand that adjust readily to sudden changes in hydrology from a dry condition to flash flooding. However, the bridge at the site that was visited spans a wide section of the flood plain, thus providing room for some lateral migration. In many other sites visited, lateral migration of meanders was a potential threat to bridge abutments. In figure 14, lateral migration of a gentle meander bend has forced the channel against the left abutment. This has, in turn, caused additional local scour at the abutment and undermining of the abutments, and could result in an unstable bridge foundation. Lateral and downstream migration of this meander would have a significant impact on the left abutment.

Figure 13. Mojave River, CA.

Figure 14. Meander migrationaffecting right abutment, Hammond Branch, MD.

One of the biggest problems created by channel instability at bridges exists at single-span bridges that are only as wide as the channel. This allows for no or limited lateral or vertical adjustments of the channel. As an example, figure 15 shows a single-span bridge across a channel that is both degrading and widening. Significant widening will result in undermining of the abutment walls.

Even for channels that are unstable, the bridge may not be in danger if adequate structural redundancy is in place. Thus, an observation of channel instability is not a sufficient condition for impending structural failure. The bridge inspector must consider what impact, if any, a channel that is deemed unstable will have during the time period between inspections, especially in the event of a large hydrologic event.

Channel stabilization measures at bridges are quite common. Given the small right-of-way at most bridges, the measures typically are placed directly at the bridge and perhaps a short distance upstream or downstream. By far, the most common type of stabilization measure observed at these sites was riprap. In some cases, the riprap appeared to be effective in holding the bank in place at the bridge. In other cases, however, riprap did not appear to be effective without significant maintenance. For example, at S.R. 445 over Roaring Run in Pennsylvania, there is a high riprap wall composed of graded riprap with a median size of about 152-229 mm (see figure 16). The purpose of the wall is to prevent lateral migration of the tight meander bend just upstream of the bridge. The wall has a bank angle of about 70E. This configuration of loose, undersized riprap in such a steep arrangement has little chance of withstanding the high shear stresses imposed on it at high flows as the high gradient stream makes this tight bend. There is already evidence of riprap wall failure, as much of the stone is deposited in the stream channel just upstream of the bridge. In other cases, stabilization efforts seem to work quite well. As an example, a cross vane has been installed just downstream of the S.R. 144 bridge over Potter Run in Pennsylvania (see figure 17). The cross vane causes the flow to pool just upstream and under the bridge, slowing the high velocity and minimizing scour under the bridge and along the banks.

RELATIONSHIP BETWEEN CHANNEL STABILITY AND SCOUR AT BRIDGES

In HEC-18, scour is defined as having three vertical components: local, contraction, and bed degradation. Local and contraction scours are caused by the bridge and occur within close vicinity of the bridge. Bed degradation, on the other hand, is not caused by the bridge and may be reach-wide or even systemwide. Channel instability includes bed degradation, but also comprises other components, based on the definition given previously, such as channel widening, lateral migration, and bed aggradation. At bridges, channel instabilities can cause:

• Channel bed degradation, which may undermine the bridge foundations.
• Channel widening, which can undermine and outflank bridge abutments and piles in the flood plain.
• Lateral migration, which can undermine abutments and permit local scour to be far more productive as the channel thalweg nears an abutment.

Channel aggradation in itself is not usually detrimental to the bridge structure, but it can lead to increased flooding and channel widening. At many of the bridges observed during this project, narrow, single-span bridges often were impacted more because small lateral movements of the channel could press the stream thalweg up against one abutment, increasing the local scour at that abutment.

Figure 15. Single-span bridge over unstable channel.

Figure 16. Riprap stabilization wall along Roaring Run, PA.

Figure 17. Cross vane downstream of bridge over Potter Run, PA.

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Page Owner: Office of Research, Development, and Technology, Office of Infrastructure, RDT Scheduled Update: Archive - No Update Technical Issues: TFHRC.WebMaster@dot.gov Topics: research, infrastructure, hydraulics Keywords: research, infrastructure, hydraulics, Bridge scour, stream stability, inspection, bridge maintenance, hydraulics TRT Terms: Scour at bridges--United States--Evaluation, Bridges--United States--Foundations and piers--Evaluation, Scour (Hydraulic engineering), Channel stabilization, Hydraulics Updated: 04/23/2012