DESIGNING BENDWAY WEIRS

1
DESIGNING BENDWAY WEIRS
2
(No Transcript)
3
(No Transcript)
4
ARE BENDWAYS THE RIGHT CHOICE?

• LOOK AT IE DATA
• ----WIDTH/DEPTH RATIO gt 10
• ----CEM STAGE IV OR V
• ----Unvegetated Pt. Bar _at_ lt 50 bankfull depth
• ----Radius Curvature/Bankfull Width gt6
• ----Rc/Bankfull Width gt4lt6

5
ARE BENDWAYS RIGHT?

• CAN POINT BAR MATERIAL BE MOVED BY FLOW?
• IS SOME SCALLOPING BETWEEN WEIRS ACCEPTABLE?
• IS CHANNEL BED AT LEAST 20 FT WIDE?
• ARE ENTRANCE AND EXIT CHANNELS RELATIVELY STABLE?

6
(No Transcript)
7
(No Transcript)
8
(No Transcript)
9
START THE LAYOUT

• PLACE FIRST WEIR AT VERY START OF ERODING BANK
• ANGLE UPSTREAM SO THAT FLOW IS DIRECTED TOWARD
  POINT BAR AND INSIDE EDGE OF BEND
• ANGLE SHOULD BE 10 TO 20 DEGREES UPSTREAM OF
  PERPENDICULAR

10
(No Transcript)
11
(No Transcript)
12
RECORD DATA

• LEFT OR RIGHT BANK
• STATION
• LENGTH
• ANGLE
• AZIMUTH (COMPASS READING)

13
(No Transcript)
14
LAYING OUT WEIR 2

• STAND IN STREAM AT KEY OF WEIR NO. 1
• TURN 90 DEGREE ANGLE DOWNSTREAM FROM WEIR
• PLACE FLAG AT INTERSECTION OF SIGHTLINE WITH TOE
  OF BANK
• MEASURE DISTANCE TO FLAG

15
LAYING OUT WEIR 2

• IF DISTANCE TO INTERSECT IS LESS THAN 4 TIMES THE
  LENGTH OF WEIR 1 ---PUT WEIR 2 JUST ABOVE TH
  EINTERSECT POINT.
• IF DISTANCE IS MORE THAN 4 TIMES LENGTH OF WEIR 1
  ---MOVE UPSTREAM TO POINT WHERE SPACING IS 4
  TIMES LENGTH OF W-1

16
(No Transcript)
17
REPEAT PROCESS UNTIL

• LAST WEIR IS LESS THAN 4 WEIR LENGTHS FROM STABLE
  POINT ON BANK
• THEN SET ANGLE ON LAST WEIR TO DIRECT FLOW AT 90
  DEGREES INTO THE CENTER OF THE EXIT CHANNEL
• (COULD BE 0 DEGREES OR EVEN ANGLED DOWNSTREAM)

18
ADJUST WEIR LENGTHS

• GO BACK AND ADJUST LENGTHS TO MAKE ENDS OF WEIR
  FORM A SMOOTH ALIGNMENT THRU WEIR TIPS.

19
RE-CHECK ANGLES

• GO BACK THRU THE LAYOUT AGAIN TO CHECK WHERE EACH
  WEIR IS DIRECTING FLOW.
• PERDENDICULAR FROM MIDPOINT SHOULD NORMALLY
  DIRECT FLOW NEAR THE TIP OF THE NEXT WEIR
  DOWNSTREAM.

20
WEIR HEIGHT

• GO DOWNSTREAM TO RIFFLE LOCATION
• SHOOT ELEVATION OF RIFFLE AND MEASURE AVERAGE
  FLOW DEPTH.
• ADD 1.5 FT. TO RIFFLE ELEVATION AND THAT SHOULD
  BE YOUR CREST ELEVATION FOR ALL WEIRS IN THIS
  SET.

21
(No Transcript)
22
(No Transcript)
23
(No Transcript)
24
(No Transcript)
25
QUANTITIES

• USE WATER SURFACE AS LEVEL AND MEASURE WATER
  DEPTH ALONG WEIR EVERY 10 FT. AND COMPUTE AVERAGE
  DEPTH.
• SUBTRACT AVERAGE DEPTH OF WATER AT RIFFLE FROM
  1.5 FT. AND ADD TO AVERAGE WATER DEPTH TO GET
  RIFFLE HEIGHT.

26
QUANTITIES

• (ALL WEIRS IN A SET SHOULD BE SAME HEIGHT ABOVE
  WATER LINE)
• FIND END AREA FOR DESIGN HEIGHT ON CHART AND
  MULTIPLY BY WEIR LENGTH TO GET VOLUME
• MULTIPLY VOLUME (CU. FT.) BY 105 LBS.
• DIVIDE BY 2000 LBS TO GET TONS.

27
(No Transcript)
28
QUANTITIES

• KEYS ARE A MINIMUM OF 5 FT. DEEP AND 4 FT.
  WIDE.
• HEIGHT OF KEY SHOULD BE APPROX. HEIGHT OF LOW
  BANK OR 2 TIMES MAX. BANKFULL DEPTH.
• COMPUTE REQUIRED STONE FOR KEYS AND ADD TOTAL

29
(No Transcript)
30
DETERMINING STONE SIZE

• USE VELOCITY CALCULATED DURING IE
• MULTIPLY VELOCITY BY 2 TO APPROX. MAX. VELOCITY
  (PROVIDES A SMALL MARGIN OF SAFETY)
• SELECT D100 STONE SIZE FROM CHART OF VELOCITY
  REQUIRED TO MOVE STONE ( IE SECTION)

31
(No Transcript)
32
(No Transcript)
33
(No Transcript)
34
(No Transcript)