xt74xg9f6122 https://nyx.uky.edu/dips/xt74xg9f6122/data/mets.xml   Kentucky Agricultural Experiment Station. 1938 journals kaes_circulars_003_317 English Lexington : The Service, 1913-1958. Contact the Special Collections Research Center for information regarding rights and use of this collection. Kentucky Agricultural Experiment Station Circular (Kentucky Agricultural Experiment Station) n. 317 text Circular (Kentucky Agricultural Experiment Station) n. 317 1938 2014 true xt74xg9f6122 section xt74xg9f6122 i
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COLLEGE OF AGRICULTURE
Extension Division
THOMAS P. COOPER, Dean and Director i
CIRCULAR NO. 317
EARTH DAMS FOR FARM RESERVOIRS
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' Lexington, Ky.
August, 1938
_ Published in connection with the agricultural extension woi·k carried on by c¤-0pera- V
hou of the College of Agriculture, University of Kentucky, with the U. S. Department of
Agriculture, and distributed in furtherance of the work provided for in the Act of Con-
gress of Muy 8, 1914.

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Fmum; 1. Crawler type tractor and tw0—whee1ed terrace grader used for bmldmg
farm reservoirs ( U
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Ear//1 Dams for Farm Rc.resr1»air.s 5 ‘ -
wm FACTORS TO BE CONSIDERED IN SELECTING A SITE
thc FOR A RESERVOIR
any Capacity of a Reservoir and Drainage Area. The area that
lm, (trains into a reservoir should not be less than 7 or 8 acres. This l
area will provide ample water lor a minimum—sixed reservoir, y
um t.{l_ acre in area and an average of 6 feet deep, which will hold 11/,
acre-[ect when lilled to capacity. An acre-loot is the amotmt ol
water required to cover an acre one loot deep. It is equal to ·
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za . r  "·i¤%;·§—· .*'  tw`,.   · tw · $:4   .· ’ ‘ `”‘  "` " ‘ ir.?  `=·  ' · .
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iéa ··lV   ai—,2 ig.-   »··i · i‘~—     ‘‘’·   $3*   ;·»     A Q
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Fmum: 3. Break in an earth dam due to overtopping at a low point caused by ex-
cessive settling of the dll. V
umu 43,560 cubic [eet or 325,850 gallons. The area that drains into the
° reservoir should equal 5 acres for each acre-loot capacity in order
that the normal rainfall during the winter and spring 1nay fill the
H reservoir before summer. Occasionally, a dam may be located
lm below a s )1`l11¤` which will assure a constant water level and Jrovide
. . .° . .
ideal conditions lor hsh culture. Care should be exercised, how-
’· ever. HOL to locate a dam at such an elevation that the high—water
level in the reservoir will cover the spring.
,~\ narrow draw between two hills makes an ideal site for a dam
]' I . . . .
H U Mid reservoir, especially when the land immediately above the dam
site is com yarativelt level, since the maximum storare ca nacity
may be obtained with a minimum yardage ol earth in a dam. Ust1—
l"l'°` ¥\ll}` such a location provides a suitable site lor il spillway to divert
¥*'“l surplus water around the dam.
(Wl Ewtporation and Sevjnzge. In selecting a site lor a reservoir, it
****1* Should be kept in mind that a deep reservoir having the same vol»
CU" UIUC as zt shallow one loses less water by evaporation and S€€[)Hg€
smce smaller areas are in contact with the air and soil. The area

 ti Kmzlizrlcv Extension Cirrizlur No. BIT
to be flooded by a dam of :1 given height or the necessary height of
dam to flood il given area may be determined during il prelin1in;11·t [hc
examination of 21 proposed site :1s explained under “Survey for :111 il H
Earth l)2llll,H on page 8. TC
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Ficumz 4. Break in an earth dam due to inadequate spillway.  
QQ
Spf/lz1w1y. lf possible. a s1te should be selected wlnch permits  
the construction of :r spillway resembling :1 wide, shallow water ,4
channel, around one end of the (llllll. Frequently the topograpliy Q
is such that tl1e spillway CHI] be constructed :1t one side of the pond  
and be entirelv inde >endent of the dam. Overflow >i >es of vitrilietl  
’  
clay, concrete or iron, placed near the top of the dam, are more  
expensive, if of sufficient capacity, than open-channel spillways, :111tl  
beca11se of possible seepage around the pipe and settling of earth
:1re apt to permit loss of water from the reservoir or fZlilll1`C of the i re
dam. \1\’here :1 da111 and reservoir are located so :1s to :1dd to the
appeztrance of il farmstead or :1 reservoir is constructed as il feature
of 21 plan for landscaping, the spillway may be directly over lllt _lm
d:1n1. In such cases, the top of the dam and lower slope must lit llc
protected by masonry which is expensive :1nd usually requires ll1€ UM
services of skilled workmen. V iw
Core lVa//. A core trench extending to subsoil ZlI](l refilled willl ml
illll)CI`\'l()llS n1:1teri:1l should be included in the plan for il small IM
earth dam, otherwise seep:1ge may occur between the earth fill antl
the original surface of the soil. The trench sl1o11ld run the lull '
length of the dam. The core of i1npervio11s niaterial or sul>S¤>|l “`ll
sho11ld extend from the origin:1l ground level to within one fool Ul l"'l
the top of the dam, thruout its length, and be not less than fl <>l` ·l "'l‘
feet in width.  

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Eur//1 l)(l7I?S for Farm R(’.Y(f}`7I{)I"I`.S` 7 I
Qht of Si]/ing of 11 I{12.s11r11111)f11. Excessive erosio11 2ll)()\'€ ll d211n lllily c21use
lllilllv the reservoir to be lilled with $C(lll`llCl]L. This hztzzird is reduced to
:11* 2111 il niiniinuni il the (ll`2lll`l2lg€ Zil`C2l is l)(jl`lll2lI]Cl]L p21sture or woodland.
TCl`l`ZlClllg tl1e drainage Zll`C2l greatly reduces silting 2lIl(l lllily be ll 1
1 , 1 111e:111s ol` increasing the (ll`2llllI-1gC z1re21 by diverting water l·]`f)lIl 2111 1
gy! _ adjoining slope to tl121t (llilllilllq to the reservoir.‘
3  ki · ‘
    A grass strip 50 to 100 leet wide 2ll`()llll(l the pond, Zll)()\'C tl1e A
  l1igll—\\’ZlLC1` lll2l1`l<, helps to prevent silting ol` the reservoir, since it
  checks tl1e velocity ol the water :1nd causes the soil to be deposited
»Y~—·*_i* . . V
  on tl1e grass r21ther than 111 the reservoir. l11 order that tl1e grass
  snip be lI\2llIll21lll€(l, it inust be protected i~l`()ll\ overgiuxiiig 2lIl(l 1
§   trzunping by livestock.
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earth
, F1Gu111: 5. A farm reservoir with 11 masonry spillway directly over an earth dam, as
)l lllC a feature in lzmdscaping.
o the
}iltlll`C M , . , , , . e . . _.
_l_ thc I/11* Szzlzsozl .8/11111/d I>1* l‘,X(l)I7Ill('([. lhe subsoil :11 il dxnn site
'I L bt Yl|0lll(l be tight or nezirlv inipervious to Witlel`. .·\ loc:1tion sl1o11ld
S ‘ . ‘ 5 1
thc he avoided where the 1lll])()l1ll(lC(l \\'2ll(fl' \\'()lll(l corer ll bed ol
as . .
gr:u1el, sand, or rock containing SCEIHIS or lZl}'Cl`S, unless such beds
lwilh ‘ il1`Ccoye111l by {ive or six l`eet ol` iinpervious soil. The nziture ol the
mm] ~l\l>soil should be deterinined by the use ol` ll soil auger or il post-
. ‘ l1ol1·1lj1»—,—C]~
ll 21111l ‘ hh '
e lull R('](l/].()}l Io l1`[1*/1Is. A site niziy be selected where tl1e reservoir
ubsoil will serve llI()l`C lllilll o11e lield. l"l`(]llCIlll}` il re:1rrzingenieiit ol
;,1i11>I` lVlli`CS will 111:1ke it possible to wziter livestock i11 several fields. l~I`0lll
i or ·l one reservoir.
1K8utucky Extension Circular No, 304, **Soil Erosion zind Its C0ntr01."

 S Kenluc/cy Extension Circular N0. 317
surwny Fox AN EARTH DAM Em
After the site of a dam has been chosen it is advisable to mark I (
the high—water line with stakes and to get data for determining the
dimensions of the dam. This information is required for estimqt. ML
ing the volume of the dam and determining its probable cost and {lin}
. . . . . _ [
the length of time required to build 1t. A farm level or survevort Il I
. . . . I Q
level is convenient in making the survey.  
m
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    ——— $3
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Fmums 6. A farm reservoir protected from silting by permanent sod, Note electric
fence to exclude livestock.
nh:
Use of Imwl io I.om1e Hfg`fI.-1lr'(lf('}` [ine. The steps to be taken the
are: at
l. Set up the level as shown in hgure 7 so that the telescope is ilu
about one foot higher than the proposed high-water mark at the or
site of the dam. The rodman sets the rod on the ground at “A", €11·
the proposed water line at one end of the site. The instrument am
man then directs the rodman to raise or lower the target until it fer
coincides with the horizontal cross hair. The target is fastened in slit
this position.
2. The rodman then crosses the draw and the instrument man ex
motions him to move up or down the slope at the other end of the ;t (
site until a place is found where the target again coincides with tht as
horizontal cross hair. This is station F. Stations A and F mark the me
water line at each end of the proposed dam but not the top of the to
dam, as explained later. he
3. The rodman then moves up the draw until the water line 15 po
found at the upper end of the proposed pond, as was point F (SW wg
tion G, Hgure 7). These three sta tions give an outline of the area
in which water will be impounded by the proposed dam. Other

 E(ll`f/I l)tl7II5 for Farm Reservoirs 9
points indicating the high—water line may be located as were points
G and F.
  Uge of Devel lo Drslcrmiuc Hcighl of Dawg ln order that an
nab ;t(·curat€·€st11H2ltQ Hllly l)€ ll1ZiCl€ ol ~IhC yélrilktge lll a proposed clam g
1 and to aid in designing the dam before construction work is started,
  it is necessary that the height ol the dam to the higli»water mark be
'OI ` determined at those points along its length where there is a change A
in the slope of the ground. Set the instrument in a position as il-
lustrated in hgure 7 and the rod at high-water line at one end ol
@4%%
7
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2 .~;;.;·¤?.Z—s...ee. rj? ~a.s.
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  -  __       ti.  
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1 Cm FIGURE 7. Use of level to locate the high—water line of a reservoir.
C C
the dam, with the target set level with the horizontal cross hair of t
aken the instrument. Record the height ol` the target above ground level .
at this station. Hold the rod at another point such as D and record
pe is the height of the target above ground level when its center coin-
t the cides with the horizontal cross hair of the instrument. The diller-
“A", ence of the two readings is the dillerence in elevation of points A
ment and D, or the height of the dam to higlrwater level at D. The dif`-
til it ference in elevation between high-water level and other points
Bd in should be determined in like manner.
lf no surveyor`s level is available and the top ol the dam does not
man exceed 200 feet in length. point F may be located bv sighting over
ml the a carpenter`s level set at A. a string may then be stretched as tight
li the as possible from A to F. to indicate the high-water level. Measure
lc the ments may then be made from the string to the ground at points A
>f the to F. The height of the string above the ground at A and F should
he O leet. Besides determining the height of the dam at various
ine is points it will be necessary to measure and record the length of each
(sta- segment of the dam as illustrated in hgure 8.
BAT? Recording Du/a. The data taken in the preliminary survey can 5
t1e‘

 lf) Kwiliic/:v Ijxicnsioii C/rcu/ur N0. 3/7
he lllt)Sl conveniently recorded in the form of il sketch, us shown '
i11 figure 8. [hc
Leve/ of .5,w//way tigu
H/ /2 wc:/er /eve/ 4 Bas.
A   _ [ _ 1 j¤· F Base
Y" b' "0l El Top
B tbl 1s; E
0 0  .
5—’0" /2C0"4"l"/0C0~ xzio 6iO  
Frczumz 8. Suggested form for recording data taken in survey.  
CORRECT DIMENSIONS FOR A DAM up
Hwig/1/. Tl1e depth of wnter i11 il reservoir is determined by '.
[lll? elevzttion of the spillwuv rztther than the l1eight of dum. A * 
lllllllltllllll difference in elevzttion of six feet between the floor of the  
storage 2ll`C2l fll](l tl1e level of the spillwztv is reconnnended. The E?
‘ height of tl1e dznn 2ll)<)\`() tl1e spillwuy should include tl1e depth of
the S])lll\\'1l>`, which mziv he o11e to two feet, 2tIl(l illl ztdditionztl foot. i
of l1eigl1t culled Ul·l`CCl)<)2ll`(l.H to reduce the llZllZll`(l of water hreatlt-
ing tl1e (lillll during periods of llC(l\'}' Tillllliilll, wl1en wztter in the
spillwtiv may he running :1t its lll2lXllIllllll depth.
Tl1e l.()ll()\\'lllg exzunple illustrzites the lllClll()(l used in deter-
mining tl1e height. of :1 dzun :1t vztrious points in its length. See l°"°l
figure l5.
Height of spillway above original ground level ............ 8 feet. H
Depth of spillway .............................,................................,..... 2 feet. ml
Freeboard ..........,................................,........................................ 1 foot.
Total height of dam .......... ll feet.  
'/`ojz ll'irf//1. The lllllllllllllll width of the top of the dam should *t<`<°
he ·l feet for dznns up to lll feet i11 height. 11nd 6 feet for dznns front *[>ll
Ifl to l5 feet in height. Tl1e type of equipment used in nioring N5]
£‘2ll`lll 111:1}* lIlill]>U¤ lttlt
is five times tl1e height. plus tl1e top width. steeper slopes 2ll`C ztpt wo
to result i11 slun1pii1g of tl1e fill when it hecoi11es wet. ztnd increzises tlit
the dillicultv of esttthlishing vegetzttion to control erosion. sor

 '4
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E(l)'//I Dani.; fAf)l`F(ll`H1 1{¢·srri‘1wii·.s ll i
»wii The following exainple illustrates the niethod ol determining
the base width of the dain at a point where the height is l l [eet (see
ligure I5).
T Base width of slope on dry side—2’ horizontal to 1’ vertical, 2 x ll' ......., 22 ft.
Base width of slope on wet side-3* horizontal to 1’ vertical, 3 x 11’ ........ 33 ft.
Top width of dam ...................................,...................................................i.............. 4 ft.
A Total base width of dam ........ 59 ft. i
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3lCl`· FIGURE 9. The top of an earth dam should be at least one foot above the highest
· _‘ level of water in the spillway. This additional height is called freeboard.
Set
lmiirr//1. The len rth ol the dain will he determined bv the ·
h t ,
width ol the draw in which the dain is located.
Size of Sjzil/way. An open-channel spillwav should he large
enough to carry water from the reservoir at a rate equal to that at
which water inay llow in lil`()l]l the drainage area. Heavy rain may
iuld occur when the reservoir is filled to capacity and an inadequate
`roiii spillwav causes lailtire olA the dain lroin over-topping. The size olA
ving a spillwav depends on the size. topography and ground cover olA the
over drainage area and the grade ol the spillwav.
con- The depth ol` an open-channel spillwav inav he lixed at l lt.,
least ll.; lt., or 2 lAt., hut the width inust vary accordingly. as shown in
tahle 2 which gives the width olA a spillwav ot a given depth. Since
to l a dam, when settled. should have at least l foot olA lreehoard ahove
side. the high-water level in the spillway. a shallow. wide spillwav per-
opes mus a greater storage capacity lor the saine height ol` dain than
rapt would a deeper and narrower one. ln sonie locations. the lav ol
eases the land determines the depth ol` spillwav. ll` loose stone or ina-
vourv inust be used to protect a water channel lroni erosion, a deep, \

 I2 [\·F}IfII(`/fj' ljxtcnsfon C1`r<·11Zur1\'o. }l7
narrow channel requires less protective material. As a general rule. ion
the depth of the spillway should increase with the drainage area exc
and the run—ofl. lf a drainage area exceeds 50 acres, or unusual chc
conditions exist which would make the success of a simple earth prt:
dam doubtful. an engineer should be employed to design the dam son
and spillway.
To determine the size of spillway:
. . . . off
lst. Determine the area of the body of land above the reservoir, A
the average slope of the ground, and the vegetative cover.
2nd. From table l determine the run-off in cubic feet per second. I
3rd. Select the hgure in the left-hand colum of table 2 which is
nearest to the run—oll in cubic feet per second as determined from
table l. The hgure in the proper column for depth. opposite the
determined figure for run»off is the width to make the spillway.
Table 1. Rates of run-off in cubic feet pe1· second from timber, pasture
and cultivated land for Kentucky (based on rainfall frequency once in
10 years).
Untcrraced Areas _ Terraced Y i
Timber Pasture Cutivated Cultivatediii
Rolling l-lilly _Rolling Hillv Qling Hilly Rolling
Area drained. 5 to 10C} 10 to 30*}} 5 to 10'}; 10 to 30'jg 5 to 10% 10 to 30% 5 to l0"}—
acres slope slope slope slope slope slope slope
2 2.9 4.5 6.7 8.8 11.9 15.3 9.2 ‘
4 5.5 7.5 12.2 15.3 21.0 28.0 15.7
6 8.3 10.7 17.5 21.8 31.0 40.5 21.6
8 11.1 13.6 22.3 27.3 39.4 50.4 26.8
10 13.8 16.3 27.2 33.0 47.2 58.8 32.1
12 16.0 18.8 31.9 38.1 54.2 66.3 37.1
14 18.3 21.3 36.1 43.2 60.2 73.5 41.7
16 20.4 23.7 40.0 48.1 66.0 80.2 46.0
18 22.2 25.8 43.5 51.7 70.1 86.5 50.1
20 23.8 27.4 46.6 55.0 76.3 92.7 54.3
25 26.9 31.5 53.2 62.6 88.3 106.7 64.4
30 29.2 34.7 58.9 69.6 98.7 119.4 73.7
35 31.0 37.9 63.7 75.1 107.0 134.0 83.0
40 32.0 41.0 67.8 80.0 114.5 150.0 93.0
45 35.0 46.0 71.0 85.0 125.0 170.0 105.0
50 50.0 65.0 80.0 98.0 138.0 189.0 122.0
iw Tabula-ted from curves prepared by C. El_§an1ser,rIl. S. DQQQSE Agricuhmc.
PROTECT A SPILLWAY FROM EROSION
\Vhere the spillway is cut thru one end of the dam. a grade of 6 i
inches in 100 feet of horizontal distance should be provided to in-
crease the velocity of water. A spillway may be protected from  
erosion by the use of dense-rooted vegetation, such as l)lllCgl`€l5$ 0f  
Bermuda grass, established by seeding or soclding. \1Vhere provis-

 Earl/1 Dams for l·`urm Resc1‘1mi1’.1 13 .
ule_ ion 1111151. l)€ 1112ldC [O1` 2111 Z*\l)1`UpL (l1‘<>p in 21 spillway, 01* the gradcg
ireu exceeds that reconinieiiclecl in the footnote to table 2, 21 niasonrv
suzil check dzini with apron should be built or the spillway should he
irtli protected from erosion by paving it with concrete or rubble ma-
lzmi S(>Ill`>’.l
Table 2. Bottom width of spillway, in fect, corresponding to given run-
. 0ff and depthii
·oii·, ,4..?-4?4Lr 11. 
Run-off, 1 foot 1l{;1eet 2 feet l
cu. ft. per sec. deep deep deep
md. rf-———·—4—·é~——— ————
. ·. 5 5 —- -
.l1 is . 10 5 _ _
l`()ll1 15 6 _ _
the 20 9 - -
25 11 - -
30 13 5 -—
_ 35 15 6 —
’°“Y" 40 17 7 -
B *7* 45 19 8 5 .
50 21 9 6
77 . 55 23 10 6%
fe 50 25 11 7 ,
ted 65 27 12% 7%
__ 70 30 13% 8
‘§, 75 — 14% 9
N 80 - 15% 9%
6 I 85 -— 16% 10
5 90 - 17% 11
7 95 - 18% 11%
5 100 - 19% 12
B 105 -— 20 % 12  i
1 110 — 21% 13%
1 115 — 23 14
7 120 - 24 14%
0 125 — 25 15%
7 130 - 26 16
3 135 — 27 15%
4 140 - 28 17
7 145 — 29 18
0 150 — 30 18%
0 155 - — 19
0 160 - - 20
0 _ 165 - - 20%
ire, 170 — - 21
175 — — 22
180 — — 22%
185 — — 23
of 6 190 — — 24
0 m` ‘ The grade of u spillway for the dimensions indicated in this table should not be less
[10111 than 0.5%. If vegetation is used in the channel to control erosion, the grader should not
Pxveed 7, 5 or 31,;% for channels 1 ft., 1175 ft., or 2 ft. deep, respectively. Side slope of
55 (11 spillivay 3 ft. horizontal to 1 ft. vertical.
UVM- 1See Kentucky Extension Circular No. 304, "Soil Erosion and Its C0ntr0l."  

 W
l·l ]\'('HII!(`/{X l£X[('}I.S`li(HI (iil`('I//(ll` No. 317
Illustration. Use of Tables to Determine Size of Spillway
l’r1»!»I11111. To determine the width of spillway for a reservoir to be filled
from a 16—acre drainage area of rolling land with a maximum slope of 10 I
percent, or 10-foot drop in 100 feet of horizontal distance, which is in grass ml
but may be cultivated in row crops.
S11/111i1111, From table 1, opposite 16 in the column "Area Drained" and
under the headings "Cultivated" and "Rolling" the figure 66 is the run—o1T
in cubic feet per second.
In table 2, read down in the left-hand column "Run-off in cubic feet
per second" to 65, the figure nearest to 66. Opposite 65, in the columns
headed 1 ft., ll; ft., and 2 ft. deep, will be found the figures 27, 12% and
7%, respectively. This means that the spillway should have a bottom width
of 27 feet if 1 foot deep; 12% feet if 1% feet deep; or 7% feet if 2 feet deep.  
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