Llagas Creek Improvement Program
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10MA PRIETA SOIL CONSERVATION DISTRICT
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LOWER LLA.GAS CREEK IMPROVEMENT PROGRAM
PLAN OF OPERATIONS
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1. Looation of the .Work
The Lower Llagas Creek Improvement Project is located in the
Lome. Prieta Soil Conservation District in Santa Clara County, approxi-
mately five miles southeast of Gilroy, California. A general looation
map of the proposed projeot is attached.
The beginning of this projeot is on Llagas Creek at the north
boundary of the Taix Company property. This point is approxima. tely
6300 feet northwest of the Bloomfield Road bridge over Llagas Creek. The
project will continue for a distance of approximately 4600 feet downstream
from the Bloomfield Road bridge to the junction of Llagas Creek with the
Pajaro River and for an additional distance of approximately 1100 feet in
the Pajaro River. Total length of the project will be approximately
12,000 feet; however, construction work probably will not be done on the
up per 4100 feet of channel until a later date, since improvement work
was done on this seotion the past year. The entire project is included
as a part of this plan.
2. Description of the Project
The project involves the disposition of runoff we. ters from the
Llagal Creek watershed during the rainy season in order to prevent pro-
longed inundation of approximately 1200 acres of low lying basin area
whioh is used as oropland and pasture. At present, surface water will
stand for many days during the winter months. The ground will then be
extremely wet far into the spring making crops late and sometimes im-
possible to plant. The project will dispose of all runoff, but will not
be capable of carrying the peak floods that oan be expeoted.
Side drainage culverts will be installed at the existing drainage
ditches and as indicated in item 4 below. Floodgates will be furnished
and installed by the individual farmer. Outlet structures are reoommended
for the oulvert outlets.
The ohannel will follow the general al ignment of the existing
waterway, as shown approximately on the plans, since this is the most
practical and economical solution to the problem. At one point, the ohannel
will be realigned to eliminate a sharp corner at the Bloomfield Road bridge.
3. Desoription of the Work
This projeot provides for the oonstruotion of a ohannel to remove
the runoff from the area of the projeot. Before construction the site will
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be cleared ot tU.1. debris, truh and other obstruction.. Special pre-
cautions \dll be taken at thi8 ~ipal1n\~ crossings. The County M~ngtneer
or SMta Clara County has a",(!'J'eed to do the nece.sary excavation and to
construct a new bridg. at the BloOf!1tield Road crossing.
The ch<<nnel Is to be ot cOMbiruatiofi eu t and 1..,... COni tructlon.
The aide elopes of the cut are to be 1-1/2 1 1 vhUe the sid. slopes ot
the till art! to be 211 with a h toot btmrt and an S toot top wid.th. The
only exception to this 18 a ..action of 6 foot top width where material
18 lbd teet, as noted in parAf:rll}:lh 4-d below.
4. !!~~citlc Itas of 1;ork
a.. S ta tion 0;.00 to hl,tOO
-;':nlarg. en.tin,,; channel by excAvating ohannel to grade vi th
25 toot bottom width and m.inimum finished depth of 11-1/2
teat. Thi. section was WlU"geO in 19S2 and. haa are. anci
grade exceeding that requirecl tor d..1gn flov. Work on thi.
s.otion may be postponed. to a later d~.tet howev..., scme
clearing of v~:et.atlon ia nec.u~snry. The elope trom station.
o,too to 22~2; 1. 0.00368 and tor remainder of reach ill 0.00169.
Approxbl.a te r1~:ht-ot-vay ia 110 teat.
b. station 4l,tOO to 491loo
rinlarge erlsUng ehmmal by excAvti'!:tlng eh"Jln\~l wi th 2.$ toot
bottom v:tdth "'.'1<3 a m1n111Nrn tin1.!!lhed depth of 12 teet. The
elope o.f the c:*uarll'1~l 18 0.00J.69. Approxlmate right-ot-wa;y'
1s 110 teet.
(1) S ta tion 41,t2$
" 30 inch drainage culvert will be installed throU@h
tho west levee a:1;, the m.llti.ng drainage d1,tch.
c. Stat.1on L9,loo to S),loo
~:nlarge exillt1ng channel by Gcave tinp: channel wi tb )0 toot
bottom width and a "'Ilnim1lll f'jn1shed depth ot l~ teet. The
slope ot the channel 1. 0.00169. #pproximate right-of-way
i. 114 teet.
(1) s u tion Sl,tOO
A )0 inch drainoge culvert will be 1nst~11ed through
the _st levee at the wsti.ng dra.inage dl tah.
d. Station 53,t00 to 611-70
Enlarge en.ting channel by eXClilvaH.n.g channel with )0 toot
bottoM tI..ldth and .. lI'linimua finished. depth of 11.7 teet. The
top width of the levee 1s 6 teet wide in this .ection, -due
1:0 the 11mi ted .ve1.l.bIe material.
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(1) Station 54100
A 30 inch drainage oulvert will be ins talled through
the east levee at the existing drainage di toh known as
Washerwoman Creek.
e. Station 61170 to 63/00
Realign and excaVll te new channel with 30 foot bottom width'
and a minimum finished depth of 11.7 feet. The dope of '
the ohannel is .0010. ApproxirrlB. te right-of-way is 110 feet.
(1) Station 61/70
The new channel will leave the a1 ignment of the old
ohannel. Looation is to be as staked and as shown on
the plan.
(2) Station ~150
A 48 inoh drainage culvert will be ins talled through
the east levee at the existing drainage ohannel. This
oulvert will furnish drainage for approximetely 9,000
aores, about half of which 1s flat land. See paragraph
7, Basis of Engineering Design, for consideration in-
volved in the design of this culvert.
(3) Station 63/00
A new bridge will be constructed by Santa Clara County
on Bloomfield Road. Minimum. single span is to be 50
foot with olearenoe heig".'l-J.t to be the height of the levee
at 63/00. Center line of the new bridge is to be
approximately 50 feet west of the center line of the old
bridge. Construction of the channel will be discontinued
at the County right-of-way and will continue downstream
on the opposite side of the road. Santa Clara CO~l:l"t;y will
provide necessary excavation within County right-of-way.
(4) Station 63/00
An irrigation water line will be removed during con-
struction and replace~upon completion of the projeot,
by the indi vi dual owner.
f. Station 63/00 to 64170
Ex cava te new realigned channel with 36 foot bottom width and
a minimum finished depth of 11.7 feet. The slope of the
channel is .000579. Approximate ri[;ht-of-way is 110 feet.
(1) At Station 64170, new ohannel will be realigned into
the existing channel.
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g. Station 64170 to 87/00
Enlarge existing ohannel with 30 foot bottom width and a
minimum finished depth of 11.7 feet. The slope of the
ohannel is .000579. Approximate right-of-way is 110 feet.
(1) Station 86/00
A 24 inch drainage culvert is to be installed through
the west levee at the existing drainage ditch.
h. Station 87/00 to 109/00
Enlarge existing channel by excavating channel wi th 35 foot
bottom width and a minimum depth of 10 1/2 feet. The slope
of the channel is .000579. Approximate right-of-way is 110
feet.
(1) At Station 109/00, Llagas Creek flows into the PajG..t'o
River.
i. Station 109/00 to 120/00
This section 18 in the pajaro River.
Remove exis ting heavy growth of large trees and brush.
Lower existing channel by excavating a half-channel section
wi th bottom width of approximately 45 feet and a depth vary-
ing from 11.5 feet to 7 feet as the levee tapers off at the
end of the project. Levee will be constructed only on the
Santa Clara County side of the river. No work is planned on
the San Bent to County side. The slope of the channel 1.
0.000579. Approximate right-of-way is 160 feet.
j. End of Project at Station 120/00
At this location, project ends. Channel below this point i.
in poor condition and a.future group projeot is reoommended
for this area.
k. General
Construction stakes will be set for line and grade by the
· Soil Conservation Distriot.
5. Water Rights
There are no water rights involved in this project.
are made only for -!:he removal of surfaoe water and d:tainage.
Provisions
The work
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contemplated. in t.hia project has been ravi&wed and cleU"~ with the
County':ng1neer ot Santa Clara County and in ~ccordanoew1th the
overall CQunty rJrain.,e flan.
6. Jtifht-ot-v.,.
Rights-of-ace..s required tor con'truction and ulntenance
of thieproject 1n aocordance w1 to"! trw plar., will be provided by the
owners thereot unc!er working agrtK\!ment between $eid own~r8 and tne
South Santa Clara VWiflY,iatl'i:r Conserv1ition Dletr:tct.
1. &a1s or "!J.g1.neertnj: ti..1~
Channel is designed to dl111pose of $vf'ace wat$I'Z'i but 18 not
deligned to carr:' peak runoff b'-om the wat.13rt:!hed. .1 mlntm.mt capacitY'
pI 1000 ct. flow wi th 2 2-foot freeboard W~l!l rl1tnned, h0i49V~r, the
Df)'..ima capacity obtQ1nGd is 162~ ets. 'This latt4r tiii';ure m~y be
/ exc_s1 vo e1.nce th...~ will b'l1\ cons1d"8bl(~ ret.ardir~ ~tri9ct from
./ the ]i"a.1ero T'i.ver channel beloW' the end of t;r~ pr{~j~ct. ~.''''i!?n with
this retardil}f! ,,::f'tlil!Ct, tile ch!\nnelahould cU'rv the ll'l!n1mum 1000 cts
tlow .
n-. South Santa Clara. Vall(!!y,att:'T Centl:eTvation District will
cowstr.tct a 7$00 aere toot dq in 19Sh. Tn1!! dam is tQ provide 4000
acre teet of lf3t,.,U' COn89M"BUon .torag~~ and 3,00 tlor~ teet .of' fiood
control .torage. Therefore, thl. project wU.l l"i9ceive some flood control
bfmen tit trOll th1.s dqm in redueti.Of;, or pt)8.l.;: flows. F!owev~t' J considerable
runoff will 000"1" ~ the lOWlJr dr'linag;;) ar'"n. b~l.ow the du. fie further
study WA. mAde of this probl_ since the ~IFO:ldJf!1ate S1.Z€ and clq:"iuity ot
th. channel and fund. available liI~4f ur,~()dy det<emMd by the South
Santa Claralfilley ',"'fIlter Conee:rvaUon District.
r...ign of' drainage c\,lverts precpmted maflY probletU.,ben
fiooda occur, fiooding trom thE:. Bide dretn~~s w111 occur at the s_
t.iDle that the tlapas 18 at nood .tJ;g~. During 9~cttptional fioodB,
th0 lE!v... and t.he entire !U"":'I! will be f'.loOO~. Th4."ret'ar.$, eulv.;arts tor
the 8ide dre1.nAgl.l!lS will act only as dr..!rlng'~ c'~lve.rta and .'ill :r..ot carry
design now. Thill! moet cri tical dr31rd'I~G ie that along Bloomfield foad
which drain! l!IOl'll8 9,!)X) .er~s, ftbout hlllt." of' which is very fiat land.
The South S~ntn Cl!ll.!'tl Vsll,,*:{,atl:!r CenserT1!t:ion District will install at
least a 4f-i.neh eulvf!'rt atth1s poin~, how~'Vi't' ~ t 1s rt~B11zedt.hl!t a
consi4erable ltt:rg~r 1n:$tellA t.ion should be m~de and that this culvert
wU.l .erve only to dr~1n th~ land .a'bcut it I!U'ld will carry only a nUlll
percentage of th e peak runoff.
8. General. Com~truct1on Plan lIllld Sch~~.
c.Qn8truction 8J:80i tic.tion. tor i,hie pro.1ect are given em. the
folloving p<9fes and t{re It put of tria pl!'LTl.
COf18vuction work will be sUp"'.rv1.sed ,101ntl;r by II. designated
representative of the South Santa Cl.ara \ll!!11e;v vater Conee.rntion District
and a r~1)rC8wltatj ve of tJle :;011 ConservRtiC'Tl r>h'trict. COn8tr'UCtion
work rill be done on an hourly buts by dr~l~nil and clea.ri1li vUl be
done by bulldozer. Final ahapin!r of the 1~-ee5 w111 be done by bulldoser.
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9.
Statement of Costs
The itemized construction costs as estimated are shown on the
attached Cost Distribution Sheet. The cost of all construction will be .
borne by the South Santa Clara Valley Water Conservation District except
for the bridge on Bloomfield Road and the removing or relocating such
structures as pipelines, fences, etc. The South Santa Clara Valley
Water Conservation District will install drainage culverts through the
levees but the farmer will furnish and install the floodgates.
10. Maintenance Program
It is recognized b.Y all concerned that a maintenance problem
will exist due to the expected deposition of silty materials from the
Llagas Creek watershed. The South Santa Clara Valley Water Conservation
District will assume full reS'pOnsibility for the maintenance of the
proposed channel.
Prepared by:
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Work Unit Engineer
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Reviewed by:
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AJ;'~ Engineer /
Concurred in:
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Area C~nservationist
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Approved by:
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Cons. Distr.
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10 a Prieta Soil Conservation District
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SPECIFICATIONS
2.00 Construction Specifications
2.01 Excavation for Cha~~el and Construction of Levees
All excavation and construction of levees shall be in accordance
with the Plans and as staked in the field.
Excavation will be done by draGline. Excavated material Trill be
properly placed and spread in the levee so as to obtain satisfactory
densities consistant With this type of equipment. Final shaping of
levees will be done by bulldozer. R~cess excavation will be
disposed of as provided in paragraph 2.04 below.
No debris, rubbish or other unsatisfactory materials will be
placed in the levees.
All work 1vill be performed in a neat and workmanlike manner
satisfactory to the South Santa Clara Valley Water Conservation
District.
2.02 Clearing
All debris, rubbish and other materials will be removed from
the construction area prior to excavating. Debris that will burn
will be stockpiled adjacent to the construct:Lon area where it can be
burned at such time and in such a manner that burning is permitted
by the County Fire Ordinance. Cana, bottles, and other debris
that will not burn will be removed, stockpiled and disposed of in
such a manner satisfactory to the South Santa Clara Valley Water
Conservation District.
2.03 Removal of Obstructions
Fences will be removed and replaced by the ovVQer at such time
as not to delay the work of the contractor. Pipelines will be removed
and replaced by the owner at such a time as not to delay the work of
the contractor.
2.04 Disposal of Excavation
Excavated materials as needed will be placed in the levees.
Excess excavated materials will be stockpiled immediately adjacent
to the levees. Said material will be removed and spread over the
adjacent land by the individual o~ners.
2.05 Installation of Drainage Culverts
Culverts shall be installed in accordance with good structural
practices.
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2.06 Replacement of Bridr~e
The County of Santa Clara will construct a new bridge
on Bloomfield Road over L1agas Creek and will remove the
existing bridge. Channel excavation incidental to this work
will also be done by the County. All "'York will meet the
requirements of the County of Santa Clara.
2.07 General
Neither the Soil Conservation Service or its employees
shall be liable for any damage to any property as a result of
this work, or assumes any responsibility for the legal establishment
of any property or boundary line.
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U.S.DEPARTMENT OF AGRICUlTURE,SOll CONSERVATION SERVICE
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J.H.CHRIST, Director
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