McKinney J.D., Warnick C.C. Microhydropower Handbook Volume 1
Подождите немного. Документ загружается.
Anchor post -
a-
.
Large rock
Note:
1 ft minimum drop over weir
. Tongue and Qroove
lumber, spiked
/
Plastic or other
-mfl
type of water seal
Upstream
face
b&
- ” ’
Q
planks
’
rrlmm
-
can be omitted if
Sandbag or
earth and clay fill
weir is temporary
INEL 2 1262
Figure 3-8. Tongue-and-groove lumber dam, with weir.
For dams less
Rdcks
and gravel
Earth\and clay
.
For dams
more
1 ft minimum
Slide-in metal plate weir
If more than one weir is used,
the bottom of each weir must be at the
same elevation.
INEL 2 1263
Figure 3-9.
Log crib darns.
.!
3-29
_ _-.
.- ._
,
/
__-_- .- ._.__. -.._. ~--
stream is unusually low at the time of meacurement, estimate the additional
depth for average flow. The depth of the weir notch should be at least
equal to the depth of the stream.
The width of the notch should be at
least three times the depth (Figure 3-7).
The tongue-and-groove dam and wei r is constructed of lumber spiked
together.
If possible, divert the stream around construction areas. Dig a
trench across the stream perpendicular to the flow. This trench must be
smooth enough so that the bottom piece of lumber can be leveled.
Clay or
earth can be used for leveling. Drive the downstream priming planks (see
Figure 3-8) 2 to 3 feet deep into the stream bed to limit seepage under the
dam.
Priming planks are wooden boards, preferably tongue-and-groove, with
one end cut to a point on one edge (Figure 3-10). They are driven into the
soil so that the long pointed side is placed next to the previously driven
piank. Then as each successive plank is driven, it is forced snug against
the preceding board.a If the weir is a temporary installation,'both
upstream and downstream priming planks can be omitted.
Drive the timber anchor post into the stream bed until solid resis'tance
prevents further driving.
Shim between the post and the tongue-and-groove
lumber while building the dam to maintain a vertical plumb on the dam.
After the lumber is in place and the weir notch is smooth, drive the
upstream priming planks and waterproof the upstream face of the dam.
Next,
P!ace sandbags or earth fill against the front face.
Avoid placing the
fill too close to the weir opening.
Water turbulence upstream from the
weir
face will affect the measurement accuracy.
Finally, at least 5 feet
upstream from the weir,
drive a post into the stream bed so that the top of
the post is level with the bottom face of the weir.
Use a carpenter's level
to assure that the top of the post and the bottom face of the weir are '
level. NOTE:
The post should be located so that it can be easily reached
from the bank'(Figure 3-11).
L
a.
Robin Saunders, Harnessing I;he Power of Water, Energy Primer, Portola
Institute.
3-30
Figure 3-10. Primi ng plank.
1267
For crib dams, use several logs stacked together like a corncrib--hence
the term "crib dam."
A crib dam consists of green logs or heavier timbers
stacked perpendicular to each other,
spaced about 2 or 3 feet apart.
Spike
these together where they cross,
and fill the spaces in between with rocks
and grave:. Cover the upstream side,
especially the base, with earth or
clay to seal the edges.
The priming planks should be driven 2 to 3 feet
deep into the soil.
Protect the downstream face of the dam from erosion or undercutting
wherever water will spill over.
This is most important during times of
heavy flow!
The spillway-
c can be made of concrete, lumber, or simply a
pile of rocks large enough to withstand the continual flow. Crib dams can
be built with the lower cross-timbers extended out to form a series of
small water cascades downstream.
Each cross-timber step should be at least
as wide as it is tall.a Finally, as with the tongue-and-groove dam, drive
a post into the stream bed at least 5 feet above the weir, and make the top
of the post level with the bottom of the weir (Figure 3-11).
a.
Robin Saunders, Harnessing the Power of Water, Energy Primer, Porto!a
institute.
c..
3-31
it can be reached
from shore
l .I
INEL 2 1269
Figure 3-11.
Relationship of weir and measuring post.
To measure the water depth above the weir, simply place a yard stick
011 the post and read the depth to the nearest l/8 inch.
The flow for mea-
sured depth is read directly' from Table 3-4. This table lists flow for
each inch of weir width.
To convert to total flow, multiply by the width
of the weir(s) in inches.
Enter the resulting value in your flow table
(Figure 3-5).
EXAMPLE: Assume that the weir is 3 feet wide and that the depth is
measured at 4-3/S inches.
3-32
TABLE 3-4.
FLOW PER INCH GF KIR WIDTH (cfs)
Inches
0
l/8
l/4
3/8
l/2
0
:
3
4
5
6
i
9
10
::
13
14
15
16
17
18
:i
21
22
23
24
25
26
27
28
29
z.
32
ii
35
0 0.003
0.008
0.0015 0.0024
0.0067 0.0080 0.0094
0.0108 0.0123
0.0190
0.0208 0.0226 0.0245 0.0265
0.0348
0.0370
0.0393 0.0415 0.0439
0.0536
0.0561 0.0587
0.0613 0.0640
0.0749
0.0777
0.0806 0.0835 0.0864
0.0985
0.1016
0.1047 0.1078 0.1110
0.1241
0.1274
0.1308 0.1342 0.1376
0.1516 0.1552
0.1588 0.1624 0.166@
0.1809 0.1847 0.1885
0.1923 0.1962
0.2119
0.2159 0.2199 0.2239 0.2280
0.2444 0.2486 0.2528
0.2570
0.2613
0.2785 0.2829 0.2873 0.2917 0.2961
0.3140
0.3186 0.3231 0.3277 0.3323
0.3510
0.3557 0.3604 0.3652 0.3699
0.3892 0.3941 0.3990
0.4039
0.4089
0.4288
0.4338 0.4389 0.4440 0.4491
0.4696
0.4748 0.4800 0.4852 0.4925
0.5117
0.5170 0.5224
0.5277 0.5331
0.5549
0.5604 0.5659
0.5714 0.5769
0.5993
C.6049
0.6105 0.6162 0.6219
0.6448 0.6505
0.6563
0.6621 0.6679
0.6914 0.6973
0.7032
0.7091 0.7151
0.7390 0.7451 0.7511
0.7572 0.7633
0.7878 0.7939
0.8GOl
0.8063
0.8125
0.8375 0.8438
0.8501
0.8564
0.8628
0.8882 0.8947 0.9011
0.9075 0.9140
0.9400 0.9465 0.9531
0.9596 0.9662
0.9927 0.9993 1.006
1.013 1.019
1.046
1.053
1.060
1.067
1.074
1.101 1.108 1.115
1.122
1.129
1.156 1.163 1.170
1.178
1.184
1.213 1.220 1.227
1.234
1.241
1.270 1.277 1.285
i.292
1.299
1.328 1.336 1.343
1.356
1.358
1.387 1.395 1.402
1.410
1.417
5/8
--
0.0033
0.0139
0.0285
0.0462
0.0666
0.0894
0.1142
0.1411
0 > i697
0.2001
0.2320
0.2656
0.3006
a.3370
0.3747
0.4138
0.4547
0.4958
0.5385
0.5825
0.6276
0.6738
0.7210
0.7694
0.8187
0.8691
0.9205
0.9728
1.026
1.080
1.136
1.192
1.248
1.306
1.365
1.425
3/4
7/8
0.0044
0.0055
0.0155
0.0172
0.0306
0.0327
0.0487
0.051i
0.0694
0.0721
0.0924
0.0954
0.1175
0.1208
0.1446
0.1481
0.1734 0.1771
0.2040 0.2079
0.2361
0.2403
0.2699
0.2742
0.3050
0.3095
0.3416
0.3463
0.3795
0.3844
0.4188
0.4238
0.4593
0.4645
0.5010 0.5063
0.5440
0.5494
0.5881 0.5937
0.6333
0.6390
0.6796
0.6855
0.7270 0.7330
0.7755 0.7816
0.8250 0.8312
0.8755 0.8819
0.9270 0.9335 -
0.9792 0.9860
1.033 1.040
1.087 1.094
1.142 1.149
1.199 1.206
1.256 1.263
1.314 1.321
1.372 1.378
1.432 1.440
3-33
From Table 3-4, the flow per inch of weir width is found to
be
From Table 3-4, the flow per inch of weir width is found to be
0.0613 cfs. 0.0613 cfs. Since the weir is 36 inches wide, the total flow is Since the weir is 36 inches wide, the total flow is
therefore: therefore:
36 x 0.0613 = 2.21 cfs . 36 x 0.0613 = 2.21 cfs .
3.3.3.1.3 Float Method--The float method is recommended for
3.3.3.1.3 Float Method--The float method is recommended for
larger streams where a temporary dam is not practical. The method is not larger streams where a temporary dam is not practical. The method is not
as accurate as the previous two, but for large amounts of water, precise
as accurate as the previous two, but for large amounts of water, precise
measurements are not as critical. measurements are not as critical.
Equation (2-l) expressed flow as volume divided by time: Equation (2-l) expressed flow as volume divided by time:
. Q t”
=-
The float method uses another definition for flow: Flow is equal to the
area of a cross-section of the flowing water multiplied by the velocity of
the flowing water--
that is, the speed with which that cross-sectional area
is moving (Figure 3-12).
This subsection discusses how to determine area
and velocity for this calculation.
Q=Axv
(3-
The float method uses another definition for flow: Flow is equal to the
area of a cross-section of the flowing water multiplied by the velocity of
the flowing water--
that is, the speed with which that cross-sectional area
is moving (Figure 3-12).
This subsection discusses how to determine area
and velocity for this calculation.
Q=Axv
(3-
where
Q
flow in cfs flow in cfs
A A
= =
area in square feet (ft2) area in square feet (ft2)
V V
=
=
velocity in feet per second (fps) velocity in feet per second (fps)
3-34
.
NOTE:
Both Equation (2-l) and Equation (3-3) exprejs flow in cfs.
To use the float method, you must determine two quantities:
0
The average cross-sectional area of the stream
e
The velocity at which the stream is moving.
To determine the average area,
choose a length of stream at least
30 feet long (the longer
the better) tha.t is fairly straight, with sides
approximately parallel.
The stream should have a relatively smooth and
unobstructed bottom.
If there are large rocks in the bed or if the stream
flow is irregular, you will have to apply an appropriate correctinr factor
to the velocity.
INEL 2 12’34
Figure 3-12. Float method for estimating flow.
To start, stake out a pain,
+ at each end of the chosen length of stream
and drive a post on each side of the bank at these points.
Connect a wire
or rope between the posts crossing the stream (Figure 3-12). Use a car-
penter's line level to level the taut wire.
Measure the width of the stream
at each crossing.
Divide the width into convenient equal segments (1 to
2 feet each). Crass the stream, tying a marker (string or ribbon) on the
3-35
-.... .
wire or rope to mark each equal segment.
With a yard stick, measuring rod,
or similar device, measure the depth of water at each marker, (It is
usually easier to measure the distance from the stream bottom to the wire
and then subtract the distance from the wire to the top of the stream.)
Add up all'the readings and multiply by the segment width.
D = (d1 + d2 + d3 + . . . dn)
(3-4)
where
D
=
sum of the depths measured,
d
=
measured depth of the stream at each marker in inches
n
=
number of markers
EXAMPLE: Assume that the stream is 20 feet wide and that wires have
been stretched across the stream in two places 45 feet apart. Find
.
the sum of the depths measured.
First, divide each wire across the stream into e-foot
segments. Since 2 divides into 20 feet 10 times, use
9 markers to identify the segments, marking the first
segment 2 feet from the shore and continuing across in
Z-font intervals. The last segment marker should be
2 from the opposite bank. Next, measure the depth of
the stream at each marker, and add up all the depths
measured.
D = dl + d2 + d3 + . . . dg = 168 in.
.Now, determine the cross-sectional area of the stream. To do this,
multiply the sum of the depths measured (D) by the width of the individual
segments (W) and divide by 144 to convert from square inches to square feet.
(3-5)
3-36
where
A
C
cross-sectional area in ft2
W
=
width of individual segments in inches
D
=
sum of the.depths measured in inches
144 =
the number of square inches (in2) in a ft2
EXANPLE:
A= 24 in. x 16y4in'
A = 28 ft2
Repeat the process at the other crossing, add the two areas together,
and divide by two to obtain an average cross-sectional area for the
selected length of stream.
A1 + A2
A= 2
where
A
=
A. =
1
A2 =
2
=
(3-6)
average cross-sectional area in ft2
cross-sectional area at the first crossing in ft2
cross-sectional area at the second crossing in ft2
number of areas added together
3-37
\
.__.
--. .
-. _ ..__. _ ~- _. -,- ,_-..,. _.. .._ -.