CIVIL & STRUCTURAL ENGINEERING CONSULTANTS
7A Barbados Avenue, Kingston 5, Jamaica, Tele: (876) 754-2154/5 Fax: (876) 754-2156
New Market Housing Development
Drainage Report
June 2006
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New Market Housing Development Drainage Report
TABLE OF CONTENTS
Overview .......................................................................................... 3
Description of development ................................................................................. 3
General soil type................................................................................................... 3
Main drainage path ....................................................................................................... 3
Method of determining surface flows................................................. 5
Drainage design criteria..................................................................... 6
Mapping of local watershed ............................................................... 7
Drainage designs ..............................................................................11
Discussion and Conclusions .............................................................13
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New Market Housing Development Drainage Report
DRAINAGE STUDY FOR THE PROPOSED SUBDIVISION NEW HARBOUR
VILLAGE IN OLD HARBOUR ST. CATHERINE
Overview
Description of development
The proposed New Harbour Village development at Old Harbour in
Saint Catherine is a 52.5 Ha plot of land to be subdivided into 840
housing lots with suitable amenities. The proposed development is
located along the Old Harbour Bay Road to the south of the Old
Harbour town and Highway 2000. The property shares boundaries with
a parochial road that borders Belmont Housing Scheme to the north,
Brampton Farms to the south, Old Harbour Bay Road to the west and
fish farms to the east.
General soil type
The predominant soil type outcropping on the proposed development
lands is called Lodge clay loams, with the following characteristics:
dominant slope range 0% - 3.5%, fair external drainage, with good
internal drainage through soil to 27.94 cm (11”) and moderate drainage
below, high moisture supplying capacity, very little erosion hazard. This
soil type is estimated to be classified as a hydraulic soil type C (SCS) as
described by the US Department of Agriculture Natural Resources
Conservation Service classification.
Main drainage path
The lands in the vicinity of the proposed site drain from north to south
towards Galleon Bay, which is west of Old Harbour Bay. These lands
are drained by several watercourses which include Fraser, Stony and
Church gullies. Fraser gully is the closest of these major gully systems
and it is to the east of the project site. The proposed site is contained in a
local watershed in the above drainage system. The watercourse for this
local watershed is centrally aligned through the site as shown in Figure
1. To the west there is a drain along the Old Harbour Bay main road that
flows into the Whim Estates gully system.
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New Market Housing Development Drainage Report
The site’s local watershed extends north to the town of Old Harbour and
drains part of the eastern section of the town. This sub-watershed can be
divided into two distinct areas, north of the railway and highway 2000
road being primarily urbanized while to the south is primarily
agricultural lands (Figure 1).
The northern and southern lands are linked by drain crossings below the
railway and highway, with the highway’s box culvert being the smaller
of the two – 2.44m wide by 1.52m high (8ft x 5ft).
The channels in the northern section are characterised by irregular crosssections, alignments and varying channel surface materials such as
concrete and earth. The existing channel in the southern section that is
aligned centrally through the proposed site is also of similar description
as the northern section but is primarily natural channels.
Proposed
Development
Local
watercourse
Gullies to receive flows from
proposed development
Figure 1Map of the proposed development site and existing watercourse that receives surface flows,
extracted from the 1:50,000 metric series.
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New Market Housing Development Drainage Report
Method of determining surface flows
Several factors influences and governs surface runoff which includes: the
intensity and duration of precipitation; the drainage area - shape, slope,
and soil type (capacity for infiltration), the channel efficiency and other
characteristics.
The Rational method of determining peak surface runoff is used for the
sub areas within the subdivision and for the channel that conveys flows
from areas north of the proposed development. That area north of the
project boundary that conveys flows through the project lands is
approximately 228 acres. The rational method can be used for areas up
to approximately 400acres.
The calculation for peak runoff using the rational method is set out
below:
Q = C i A x 1/Ku
Where:
Q = Flow, m3/s (ft3/s)
C = coefficient of runoff (dimensionless)
i = rain intensity mm/hr (in/hr)
A = drainage area, hectares, ha (acres)
Ku = units conversion factor 360 (1 in English units))
Rain data is taken from the National Meteorological Service’s estimates
of maximum 24 hour rainfall for selected return periods. This is
converted to rainfall intensity by the following equation.
i = 4.73 x R
(12.25+D) 0.65
Where R = 24-hour rainfall.
D = Duration of the design rainfall event equal to the time of
concentration
The runoff coefficients by hydraulic soil group and slope range used in
the rational method were developed by Rawls et al. as shown in table 7.6
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New Market Housing Development Drainage Report
in the standard handbook of environmental engineering (by Robert
Corbitt).
The proposed development is located between the Old Harbour town
and Old Harbour Bay however the rain data used is for Old Harbour
town (see Table 1) as this is slightly higher and part of the local water shed
extends to the Old Harbour town.
Table 1 Rainfall Data
Error! Not a valid link.
The surface flows for the central main drain are shown in Table 2 below.
Table 2 Surface flows for main central drain
Error! Not a valid link.
Drainage design criteria
The Jamaica Institution of Engineers recommended “Guidelines for the
design and Construction of Housing Infrastructure” Vol 1: 1984 Storm
Water Drainage recommends that the design storm frequency of storm
sewers be 2 years and for culverts, bridges and flood control projects a
minimum of 10 years.
In the Standard Handbook for Civil Engineers by Merritt, Loftin and
Ricketts article 14.9 states “Flooding problems and surface drainage as
concerns of community and regional planning studies, differ primarily in
degree of severity. The principal concern with flooding is the desire to
avoid injury and loss of life and reduce property damages caused by
major floods (those having a recurrence interval of 25 to 100 years).
Surface-drainage systems on the other hand are primarily concerned
with convenience and providing access to property in relatively minor
storms (those having a recurrence interval of 2 to 10 years)”.
Investigations were conducted for the 1 in 25 year event for the main
drainage channels and 1 in 10 year event for the subdivision drains.
The Hydraulic structures were designed with a minimum freeboard of
1/3 the design depth in open drains while storm sewers were designed
flowing full.
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New Market Housing Development Drainage Report
It is recommended that the floor levels are to be set a minimum of 0.41m
above the road centreline. This is to allow for the road reservation to
convey the 1: 50 year storm water estimated flows without inundating
the floor levels.
Mapping of local watershed
The outline of the local watershed that affects the proposed subdivision
is shown below in Figure 2 Plan of Local watershed.
The watershed to the east of the local watershed is drained by Fraser’s
Gully and the watershed to the west is drained by watercourses on the
Old Harbour Bay main road and in the lands known as the Whim.
Mytons /
Frasers Gully
Proposed
Development
Ridge delineating
watershed
Existing
Watercoure
Figure 2 Plan of Local watershed
The start of the watershed is approximately 0.85Km north of the Old
Harbour main road and approximately 0.7Km east of the road to
Bannister.
The ridge to the east is generally aligned to the south east and terminates
just north of the confluence of the local watercourse and the Frasers
Gully.
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New Market Housing Development Drainage Report
The ridge to the west is generally aligned parallel to the Old Harbour
Bay road and just to the east of it.
The surface flows from the Bannister Road and the Old Harbour town
centre convey flows along the Old Harbour main road (as shown in
photos numbered 1-3 below) that drain in watercourses southward onto
the Whim lands.
Photo 1 View of Old Harbour Town Centre from the road to Bannister
Photo 2 Culvert conveying flows from Old Harbour centre
Photo 3 drain downstream of culvert
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New Market Housing Development Drainage Report
The land use in the local watershed is mixed but can be considered as
urban with some large open areas and agricultural use.
The watercourse in the local watershed cross both the railway and
Highway 2000 as shown in the photos below.
Photo 4 Railway Bridge
Photo 5 Highway 2000 Box Culvert
The drained area north of the development within the local water shed is
approximately 106 hectares.
Photo 6 Drain on north parochial road
Photo 7 Existing culvert crossing north parochial road
The local watershed is approximately 157 hectares from the start of the
watershed to the southern boundary of the proposed subdivision.
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New Market Housing Development Drainage Report
Photo 8 Existing drain south of site
The watercourse discharges into a detention pond that overflows into a
channel that forms a confluence with the Frasers Gully as shown in
Figure 3.
Local water shed Northern section
Old Harbour
Centre
Railway
Location of
Photo 3
Local water shed –
Southern section
Proposed
Development
Detention
Pond
Figure 3 Aerial photograph showing the Proposed site in delineated drainage area
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New Market Housing Development Drainage Report
Drainage designs
This report will consider only the main drainage features for the project.
The main central drain will replace the local watercourse (as shown in
photo 6) where it travels within the project lands.
The main central drain is sized to convey the 1:25 year return storm
flows and the subdivision drains are sized to convey 1:10 year return
flows.
Manning’s Open Channel drain design method
The Manning’s method of determining velocity of channel flow is used
to size the drain cross sections. An outline of the method is shown
below.
Variables
[] indicates dimensions
A = Flow cross-sectional area, determined normal (perpendicular) to the bottom surface
[L2]
b = Channel bottom width [L].
F = Froude number. F is a non-dimensional parameter indicating the relative effect of
inertial effects to gravity effects.
Flows with F<1 are low velocity flows called subcritical. F>1 are high velocity flows
called supercritical. Subcritical flows are controlled by downstream obstructions while
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New Market Housing Development Drainage Report
supercritical flows are affected by upstream controls. F=1 flows are called critical.
g = acceleration due to gravity = 32.174 ft/s2 = 9.8066 m/s2. g is used in the equation for
Froude number.
k = unit conversion factor = 1.49 if English units = 1.0 if metric units.
n = Manning coefficient
P = Wetted perimeter [L]. P is the contact length between the water and the channel
bottom and sides.
Q = Discharge or flowrate [L3/T].
R = Hydraulic radius of the flow cross-section [L].
S = Slope of channel bottom or water surface [L/L]. Vertical distance divided by
horizontal distance.
T = Top width of the flowing water [L].
V = Average velocity of the water [L/T].
y = Water depth measured normal (perpendicular) to the bottom of the channel [L
z1, z2 = Side slopes of each bank of the channel.
The manning friction coefficients used are shown in the table below.
Material
Manning n
Natural Streams
Material
Manning n
Excavated Earth Channels
Clean and Straight
0.030
Clean
0.022
Major Rivers
0.035
Gravelly
0.025
Sluggish with Deep
Pools
0.040
Weedy
0.030
Stony, Cobbles
0.035
Metals
Floodplains
Brass
0.011
Pasture, Farmland
0.035
Cast Iron
0.013
Light Brush
0.050
Smooth Steel
0.012
Heavy Brush
0.075
Corrugated Metal
0.022
Trees
0.15
Glass
0.010
Finished Concrete
0.012
Clay Tile
0.014
Unfinished Concrete
0.014
Brickwork
0.015
Gravel
0.029
Asphalt
0.016
Earth
0.025
Masonry
0.025
Planed Wood
0.012
Unplaned Wood
0.013
Non-Metals
Corrugated Polyethylene (PE) with smooth inner walls
0.009-0.015
Corrugated Polyethylene (PE) with corrugated inner walls
0.018-0.025
Polyvinyl Chloride (PVC) with smooth inner walls
0.009-0.011
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New Market Housing Development Drainage Report
Table 3 details the estimated flows in the open and the central main
drains. The return period for flow estimates are shown in the table. The
drain reservations are a minimum of 3m wider than the top width of the
drain structures whereby surface water will always have a route for
through flow in extraordinary events.
Table 3 New Harbour Village Drain Sizing
Error! Not a valid link.
Discussion and Conclusions
The drainage concept is to allow for major storm water flows originating
north of the proposed subdivision to flow through the project lands
without a major effect on the proposed subdivision.
The subdivision roads and drain reservations are graded to provide clear
flow paths that will convey surface flows into the main central and
existing downstream watercourses during extreme rain events.
An existing detention feature receives surface flow just south of the
project lands that will allow for reduction in stream velocity and peak
downstream discharge.
Floor levels will be set a minimum of 0.41m above road finished
centreline grades. Houses constructed adjacent to proposed drains will
be raised a minimum of an additional 0.2m to allow for a greater flow
capacity in the road and drain reservations.
Attachments include spreadsheets showing the sub-drainage areas and
the resulting surface flows that were used to size the pipe culverts.
Open and recreational areas are sited around the main central drain
throughout the project lands. A longitudinal park a minimum of 32m
wide to the east of central main drain will provide additional area for
surface flows if an extreme event was to occur. At the discharge of the
central main drain there are two large parks that can detain water if
excessive flows or blockages were to occur.
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New Market Housing Development Drainage Report
The residents in the area that were interviewed say that flooding is not a
problem in the area except for the 36” diameter pipe culvert shown in
photo #7 being overtopped from time to time and causing localised
problems. That pipe culvert will be replaced by a 3.6m wide by 1.5m
high culvert therefore this project will improve the overall drainage in the
area.
Prepared by
I. A. Foreman PE
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