Report on Damages Done to Jennings and Perseverance Systems, April 2011

7/23/2019 Report on Damages Done to Jennings and Perseverance Systems, April 2011

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St Vincent and the Grenadines

Central Water and Sewerage Authority

Report on damages to the Jennings and

Perseverance Treatment and Supply Systems

and Restoration works April !""

Prepared #y$ %ngineering &epartment

&ate$ "'th(ay !""


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Table of Contents

Introduction

Outline of the Damage sustained to CWSA systems and Installations

Restoration and Repair works

ist of !ipes and "itting used during disaster relief

ist of construction materials used during disaster relief

ist of #$uipment and %achinery used during disaster relief

abour force used during disaster relief

Introduction


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)n the ""tho* April !"" heavy rain*all in the Perseverance and Jennings

valley+ "", and "!, respectively+ resulted in swollen rivers and severe

-ooding that in turn caused signi.cant damage to two o* our ma/or systems

on the windward side o* the island0 The a1ected systems were Jennings

Treatment and Supply system also known as the Windward Supply Pro/ect

and the Perseverance Treatment and Supply system that *eeds Georgetown

and surrounding areas0 The o#/ective o* this report is to document the post

disaster e1orts o* the Central Water and Sewerage Authority as it relates to

the reha#ilitation works done on our systems and its inter*ace with the

community in #oosting its resilience to cope with intermittent water

shortages0 An added e2pectation is that this report will assist in

supplementing a *avoura#le institutional *ramework to strengthen even

*urther our disaster management plan0


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Outline of the Damage sustained to CWSA systems and

Installations

On the !erse&erance system the ma'or damages were sustained in

the following areas(

(assive agglomeration o* #oulders+ logs and sediments at the intake

dam as well as a #uild up o* sediments in the grit cham#er rending

#oth una#le to *unction0

#reakages on the 3, ductile 4ron pipeline *rom the intake to the

Treatment plant0

At the 5!+!!! gallon storage tank over-ow the pipes were swept

away and outlet valves were shi*ted as well as an accumulation o*

sediments within the tanks cham#ers0

6evel sensors and 7low meters *rom the water resources pro/ect were

swept away #y the swollen river0

There was also scouring at the #ase o* the storage tank that may

threaten the structural integrity o* its *oundation and degradation o*

the slopes #etween the road and the tank that will re8uire retaining

structures to sta#ili9e same0

A '5!: section o* *ence closest to the river was swept away0

' ;reakages on the 3, ductile 4ron transmission main *rom the

treatment plant at the 'rd+ )ne at its river

crossing in Spring+ Georgetown and the other at the river crossing at

(ount ?oung where it supplied water to Chester Cottage0

" ;reakage on the


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There was also the *ailure o* a retaining wall that supported a portion

o* road a#ove the river #etween the .rst and second river crossing0

The #ridges were signi.cantly damaged as they were clogged in most

instances and the water eroded the weaker portions #e*ore and a*ter

completely destroying the roads and in some cases scouring their

*oundation and a#utment walls0

On the )ennings System the ma'or damages were obser&ed in the

following areas(

;reakage on a section o* the =, pipeline *rom the intake to the

treatment plant as a result o* a mass movement o* a signi.cant portion

o* the land0

The gate and '

one at the stream in *ront o* nights property+ two in the pro2imity o*

the hill a#ove knights #ridge+ one close to knights #ridge+ one en route

#etween ;yrea and Jennings at the .rst wash out and two suspended

river crossings at ;yrea proper0

The roads sustained similar damages to those in the perseverance

valley> high volumes o* sediments and huge logs rendered them

impassa#le0 4n some sections where the road runs parallel to the river

there was mass erosion o* the river #anks that signi.cantly reduced

the width o* the carriageway as well as landslides that causes road

#locked0


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The #ridges and river crossings were not as #adly a1ected and were

mainly #locked hence a1ecting their *unctionality and not their

structural integrity0

There was also damage done to the


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Cleaning o* the intake also #egun on that day as well as shuttling o* Pipes *rom

;elair Comple2 to ;yrea as the ;ridge at (t0 ?oung and conse8uently the #ridge at

;yrea were impassa#le0 )ur assessments continued until Thursday the "

T& B and G


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changes its course0 There are also plans in place to cover the pipeline

with mould or sand *rom the river #ed to act as a cushion and reduce

the vulnera#ility o* the pipes with respect to the ad/oining slope0

The .tting at the Storage tank over-ow were replaced on the B thand

3tho* April while the removal o* de#ris and -ushing o* the tanks weredone on those days #y la#ourers0

The #reakages on the 3, lines were repaired strategically *rom the 'rd

crossing upwards towards the treatment plant0 )n "= th o* April

lengths o* 3, -anged ductile iron pipes were .tted along the third river

crossing+ concrete works are yet to #e carried out at this point0 )n the

"Btho* April lengths o* 3, #ell H Plain and lengths o* 3, 7langed

pipes were used to restore the

thick layer o* concrete around '!: o* the pipe surround where the river

is e2pected to -ow0 (i2ing o* concrete was done #y mi2er with a mi2

ratio o* "$$< and the mi2 was transported #y ;uggy+ this was done

#etween the "3thand the "tho* April0

4n the second phase the 3,pipeline that was previously laid was

#ack.lled using sand that was transported *rom &ickson+ Georgetown

#y ;uggy and with the compliments o* (r Selwyn &a#reo0 The rivercourse was then diverted over to the concrete protected section o* the

pipeline again #y (r Austin ;ullock who also did the trenching *or the

second phase0 We then proceeded to /oin the pipes to the e2isting

pipeline at the other e2treme o* the river #y installing a *urther 5 I

lengths o* 3, &040 pipes0 )nce this was completed we then placed

concrete protection over a *urther !: o* pipeline as the natural course


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o* the river in that areas is #oth unpredicta#le and is also lia#le to

change when the #ridge is reconstructed hence a very conservative

approach on our part0 The concrete works were 8uite challenging as

the tires o* our #uggy were punctured on various occasion and we had

to resort to the use o* the ;ackhoe G


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&040 *rom the treatment plant+ concrete works were then carried out at

a later date0

The Chlorination *acility has since #een cleaned #y la#ourers+ the

#reakages on the ", chlorine line and the chlorine sample point stand

pipe has also #een repaired0

Repair works on the ", transmission mains are as *ollows$

At the two suspended river crossings at ;yrea one length o* ", &040

-anged pipes was used in #oth instances as well as a -anged adaptor0

At the .rst washout *rom Jennings in the direction o* ;yrea I lengths

o* ", &040 -anged were used to repair that section0

Close to knights ;ridge where originally there was ;ell and Plain Pipes

that were washed away+ ' lengths o* 7langed pipes were used as well

as welding to e1ect the anchors0

4n the pro2imity o* the hill a#ove knights the two #reakages re8uired =

I lengths o* ;ell and Plain pipes to reinstate that segment+ and < I

lengths respectively0

The stream in *ront o* knights ;uilding ' I lengths o* " &040 -anged

pipes were used to replace the ;ell and plain pipes o* the same

diameter that e2isted there0 Concrete works were also done throughout

at all o* these locations to secure the pipelines #y providing thrust

#locks+ anchors and Supports0

The damaged


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"K ;ell and Plain &040

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Documents

Report on Damages Done to Jennings and Perseverance Systems, April 2011