City of Larkspur - Request for Proposals – Storm Drain Master Plan October 1, 2018

Attachment C

ATTACHMENTS C

CITY OF LARKSPUR STORM DRAIN MASTER PLAN 1988,

LARKSPUR CREEK CHANNEL STUDY 1989 AND

GREENBRAE STORM DRAINAGE STUDY 1987

STORM

REENBR~E

DRaINaGE STUDY

PROJECT NO. ECR71~

Pr-epnr-ecl bu

COUNTY OF MRR!N

DEPRRTMEN~T OF PUBLIC WORKS

Julg 1987

TRBLE OF CONTENTS

SITE I]ESCEIPTION ................. 1

UICINITY I'IRP ................... 2

SCOPE OF ORR INROE STUDY ............. 3

ORT~ COLLECTI ON ................. ~ 1

HYDROLOBY/HYDRRUL I CS .............. S

RECOMMENDAT IONS ................. B

Rt-eo R ................... 8

Arco B . . ................. 9

Rroa C ................... 10

The purpose, oF this studw wes to collect data on the existing

storm drain culverts in the public rights oF wow end

easements within the studw oreo, perform h~drologu end

hUdroulic calculations, end recommend improvements, os

needed, For these Facilities. These recommendations opplw to

the entire drainage swstem (both Larkspur and Countw oF Matin

portions) located between Sir Francis Drake Boulevard end the

northerlu top oF the watershed. The Follo~ing is o detailed

explanation oF the methods and criteria used For each oF

these tasks.

D~T~ COLLECTION

1! o~ the cuZverts or drainage ~acllittes were numbered and

shown on o topographic map entitled "GR££NBR~£ DRaINaGE

STUDY, CULUERT LOC~TION M~P" on Eile with the Countw o~

Narin, Department o~ Public Uorks. The'culverts or drainage

ocl~lties within oreo NAN and O portion o~ the culverts or

drainage ~acllities within oreo NBN were ~leld located.

In~ormotion o~ the remainder o~ the culverts or drainage

acllities within oreo NBN end Oil O~ the culverts or

drainage ~ociiities within area NCN woe obtained ~rom

previous ln~ormation on ~lie in the ~arin Countu Deportment

o~ Public WorkS. The exact dote and the dote collection

method used to obtain the previous in~ormotion is unknown.

Where ~leid located, the size o~ each culvert was measured.

The slope o~ each culvert was assumed to match the slope o~

the ground above it. The length o~ the culvert was scaled

rom o-topographic map.

HYDROLOBY/HYDRRULI~S

fl hwdrologu, mop end hudrologu/hudrauXic co~cu~otions for this

etudw ore on fiXe in the Herin Countw Deportment of Public

Works. The studw oreo mos divided into three main droinooe

areas end each of tl~ese areas mere further subdivided into

smo~ler ormos to calculate the flom In each culvert, The

Rotiono! flethod mos used to calculate storm meter runoff, end

the storm meter quantities from these calculation hove been

entered into the data sheets for each culvert. These dote

sheets are on file. in the rlorin Countw Deportment of Public

Works.

A ten-wear design storm mos used to calculate storm water

quantities for areas less than ~0 acres, and a tmentu-f~ve

wear design storm mas used to calculate quantities for

culvert drainage areas containing ~0 acres or more.

ecommendations For the replacement oF storm drain

within each oF the three main drainage areas ore shown on the

Following sheets. ?he dashed lines indicate where the

exlstino storm drain pipes ore adequate to handle the design

Flou. The solid lines .show where the existing storm

pipe diameters £number In parenthesis) are inadequate end the

diameter oF the pipe required to corfu the design Flow.

existino and replacement pipes ore rein~orced concrete pipes,

unless otheruise noted on plan.

The maJoritw oF the pipes to. be replaced ore located within

the rood right oF woU and normal construction techniques con

be used. However, within oreo 'B', the pipes to be replaced

between Los Certes end Sir Francis Drake Boulevard ore

located within drainage easements where residences are

located-within close proximitg. Specie! construction

techniques could be required to prevent damage to the

ex~st~ng dwellings. ~ more econom~co! approach might be to

divert some oF this drainage into o ne~ drainage s~stem that

would extend the Lo Cuesta drainage pipe et Los Certes

southerl~ to Sir Francis Drake Boulevard end .then wes~erlg