Streambank Protection Design of Riprap Protection

1. Streambank ProtectionDesign of Riprap Protection Stephen T. Maynord

2. Objectives: Following this lecture, the students will be able to: 1)Use riprap in different ways on streambank protection projects. 2)List significant riprap design factors common to most of the different ways of using riprap. 3)Describe significant design features associated with toe protection. 4)Determine riprap size, gabion size, and estimate scour depth in bends using PC program “Chanlpro”

3. Objective 1: Use riprap in different ways on streambank protection projects. Goal: Use minimum amount of structural protection required to accomplish project objectives. Achieving this goal could result in the following ways to use riprap:

4. Standard revetment constructed over the entire bank Upper bank protection Lower bank protection Toe protection Launchable stone protection such as windrow, trench-fill, or weighted riprap toe Indirect protection- dikes, hardpoints, bendway weirs- to be covered by others Environmental benefits

19. TRENCHFILL REVETMENT

25. Streambank ProtectionOBJECTIVE 2:DESIGN FACTORS & FAILURE CAUSES Design & failure can be scary!!!!

26. A.) RIPRAP CHARACTERISTICS • UNIT WEIGHT - >150 LBS/FT3 • SHAPE – BLOCKY RATHER THAN ELONGATED • ANGULARITY – ANGULAR BEST ROUNDED = 1.25* ANGULAR • SOURCES – ROCK QUARRIES, BROKEN CONCRETE, STREAM ROUNDED STONE? HAS YOUR OFFICE USED ANYTHING OTHER THAN CRUSHED ROCK FOR RIPRAP?

30. C.) LAYER THICKNESS • SIGNIFICANT IMPACT ON STABILITY • NOT LESS THAN d100(MAX) OR 1.5 d50(MAX) • THICKNESS > 1 d100(MAX) ALLOWED REDUCTION IN STONE SIZE • UNDERWATER PLACEMENT REQUIRES 50% INCREASE

31. D.) SIDE SLOPE INCLINATION • RARELY STEEPER THAN 1V:1.5H • 1V:2H TO 1V:3H PREFERRED • STONE SIZE LARGE WHEN BANK ANGLE APPROACHES REPOSE ANGLE • REPOSE ANGLE VARIES WITH SLOPE HEIGHT • SLIDING PROBLEMS ON FILTER FABRIC LIMIT TO 1V:2H • GEOTECHINICAL STABILITY OFTEN DEFINES LIMITING SLOPE ?WHAT SIDE SLOPES ARE USED IN YOUR AREA?

32. E.) FILTER REQUIREMENTS(PRIMARILY A GEOTECH RESPONSIBILITY)FILTER PURPOSES: • PREVENT STREAM TURBULENCE FROM REMOVING BANK MATERIAL • PREVENT GROUNDWATER FROM MOVING BANK MATERIAL THROUGH RIPRAP • SERVE AS FOUNDATION SUCCESSFUL REVETMENTS HAVE BEEN CONSTRUCTED WITHOUT A FILTER ? DOES YOUR OFFICE REQUIRE A FILTER?

34. F.) REVETMENT HEIGHT • TOTAL BANK PROTECTION • PARTIAL BANK PROTECTION -REDUCED STONE VOLUME -PROVIDES ENVIRONMENTAL BEEFITS -DEPENDS ON: -HYDRAULIC FORCES -BANK MATERIAL STRENGTH -VEGETATION -HYDROGRAPH -SUCCESSFUL IN SECTION 32

39. G.) VEGETATION IN RIPRAP • ADVANTAGES -LESS MAINTENANCE -ENVIRONMENTAL BENEFITS • DISADVANTAGES -DIFFICULT TO INSPECT -INCREASED WATER LEVELS -TURBULENCE INCREASE -LARGE TREE REMOVAL • ? WHAT ARE DISTRICT VEGETATION PRACTICES?

41. H.) TRANSPORT AND PLACEMENT • TRANSPORT OFTEN MAJOR PART OF COST • TRUCK $ = 10 * BARGE $ • DUMPING AND SPREADING PROMOTES SIZE SEGREGATION AND BREAKAGE • RELEASE NEAR FINAL POSITION? COMMENTS ON TRANSPORT AND PLACEMENT

42. Streambank ProtectionOBJECTIVE 3:TOE PROTECTION

45. TOE SCOURDESIGN • ESTIMATE MAXIMUM SCOUR • PROTECT AGAINST MAXIMUM SCOUR

47. SCOUR DEPTH DEPENDS ON: • CHANNEL PLANFORM • CROSS-SECTION • VELOCITY, SHEAR STRESS • WATER AND SEDIMENT HYDROGRAPH • BED MATERIAL SIZE AND GRADATION • BANK ERODIBILITY COMPLEX PROBLEM. THE FOLLOWING TECHNIQUES ARE AVAILABLE FOR SCOUR DEPTH ESTIMATION

48. TOE SCOUR ESTIMATIONS • EXPERIENCE AND “RULES OF THUMB” (MOST WIDELY USED METHOD) -MAXIMUM SCOUR WILL BE A CERTAIN DISTANCE BELOW THE DEEPEST POINT IN THE EXISTING CROSS-SECTION