ON IMPROVEMENT OF AN URBAN DRAINAGE SYSTEM
Of Moratuwa,Jaffna,[email protected]
Dr. Kasun de Silva,
Dr. Nimal Wijeyaratna, Dr. Lalith Rajapaksa
rainfall event is the main reason for very heavy flooding. This occurs because
of the urbanization in the cities. the urbanization causes the natural
unbalance between effective drainage capacity and generated urban runoff.(Kong, Ban, Yin, James, & Dronova, 2017)
To stop this unbalance, we must have a proper drainage system. the drainage
system is disturbed due to solid waste deposited in the channels.so we must
maintain proper drainage channel to move the runoff
very effectively. We must consider hydrologic impact assessment to design the
storage and urban drainage system. When we model the drainage, a system using SWMM (Storm Water Management
Modelling) software input the pre-and post-hydrological model to analyze the existing drainage system. Then we
must consider flooding issues and sewage water mixed with rainwater and other water-related issues to come up with the new design. The drainage system I design should consider
the groundwater protection because there are a lot of
species inside the ground.(Nadeesha Chandraseana, Wan Yusof, Ul Mustafa, Mustaffa, & Umar, 2016)
Keywords: Heavy flooding;
urbanization; solid waste; runoff; ground water
Flooding is the natural disaster. These disasters we
can’t control by our hands. We can control only by protecting the nature. This
flooding disaster causes severe damages to people as well as properties. This
disproportionate impact in densely populated cities may affect flooding heavily.
This occurs normally in the downstream areas where people are living in
informal settlements. For them it is frequently occurred. When we consider the
affected people are mostly the low-income people in Colombo city. The victim of
these natural hazards is mainly affected by without pre-warning is given by the
Chandraseana et al., 2016)
The main goal of this research
Give a good
drainage system to the critical area in Colombo city.
Modify the land
profile for efficiency of the surface run off.
In Colombo city is becoming very sensitive areas
because of high level organizations are established in this area. So, the
urbanization is the most commonly occurred in this area. These also leads to flooding.
We can call this as increases of impervious areas causing these issues. When we
analyse the real scenario of the Colombo city higher peak flow and shorter time
to peak is the main factor affects the flooding. The intensity of precipitation
also increases due to various reasons like climatic changes. That also causes
high run off in the downstream areas.(Trenouth,
Gharabaghi, & Farghaly, 2018)
To overcome this issued we have to have a proper
drainage infrastructure should be developed. We must model a drainage system in
SWMM for the pre-and post-conditions. Then only we can come up with every
difficulty in the existing drainage system. As all know this is fully
computerized model we can model different types of model find the final
effective drainage model.(Rathnayake, 2015)
Not only modelling drainage system leads to stop the
flooding. We must maintain the properly otherwise it will not continue functioning.
People also put their solid waste in near the open space this also leads to
block the drainage.it reduces drainage capacity. So, people also think about
this as well. That’s for their own benefits.(Kong et al., 2017)
When we consider the drainage is one of the least
concentration factor in urban development cycle. This tends to decrease the efficiency
and workability. Main problem in srilanka is very low finance allocation for
the drainage infra structure.
Consider all these effects we have to design an
effective drainage to consider all the safety issues of the people.
We have considered the critical area which is
sensitive area in Colombo. Here the area we consider is Kelaniya. Which is
consisting of 450 hec area. This consist of mixture of residential areas,
roads, marshy areas. The Kalani area is 1.50 m above the mean sea level. this
existing drainage system is constructed in 1910.
Figure ?1 General
Outline of the study area
continue our further study of flood management based on the topographical map
in Kelaniya area. then only we can clearly identify the land profile. After
that we can identify which land area should be cut or fill depend on their
present condition to make the runoff efficiently.
reason is unplanned urbanization in the downstream area which is heavily
affected the flooding. the solid waste management should well organize
otherwise it will also block the drainage channels. We have to give the solution
for the drainage system in the sensitive area.
Urban drainage cycle
hydrological cycle shown in figure- 2 should be well organized otherwise it
will also leads to flooding. normally hydrological cycle starts with
precipitation. It is fully developed by rainfalls. It also creates overland
flow. As well as ground recharge done
by infiltration. there is an initial loss governed by evaporation. This cycle
can be implement very clearly by the below diagram.(Nadeesha Chandraseana et al., 2016)
of the ground also affect the flooding in the considerable amount.so we can see
the relationship between imperviousness. The equation (1) and (2) clearly state
? runoff volume (1)
Imperviousness ? 1/Infilt. Volume (2)
Figure?2 Schematic representation of urban drainage cycle
(Nadeesha Chandraseana et al., 2016)
about computer modelling in storm water management Model(SWMM)
software is commonly used hydraulic software for designing planning analyzing
used in srilanka. SWMM software can design a pre-model using the data of
existing drainage system get from CMC and run in this software and find out the
problem in this current system. Then we can get the idea of the land profile
and existing runoff patterns and design a post model in SWMM software this
leads to help us to find a effective and economical way.
software we can analyze for different scenario. This software basically models
with quantity and quality of runoff made within each catchment before modeling
in SWMM software we must identify the sub catchment area which can causes the
heavy runoff in our segment.
analyze and come up with different implementation depend on our analysis
changing rainfall due to the climatic changes and man-made effects to the
in the surface run off
of the rainfall in to unsaturated soils.
A symmetrical form of current urban structure affects the urban drainage
cycle. In present condition urban areas are without any prior control people
are making administrative, industrial and residential areas. They are not
considering the formal zoning plans over the cityscape. The negative effect of
urban drainage cycle is disposing the solid wastes in the critical sensitive
areas. Likewise, population agglomeration affects the flooding plan.(Jang et al., 2007)
Sample data obtain from Colombo municipal council to obtain drainage
capacity needed for the area.
rainfall November 2013 =375mm/h
Colombo Municipal Council = 37 000 m2 Runoff coefficient for urban area = 0.6
volume = rainfall X Area X Runoff Coefficient Runoff volume = 8,325,000 m3
amount to a volume of 8,325,000 m3 from a 375 mm of rainfall.
length of drainage area of CMC is 350,000 m. The drainage section is
rectangular and the dimensions varying from 1m-0.6m. Average width and depth of micro drain canal
is about 1m.
= length X Width X depth
= 350x 103 m x
1 m x 1 m =
350, 000 m3
Drainage capacity: Runoff volume = 0.0420
consider the present and future imperviousness of landscape scenario from the
CMC data sheet. because land scenario may change due to the past flooding and
urbanization effects. When flooding occurs the land, profile might change
slightly because of soil erosion and other related parameters.so when we are
designing we must consider these effects as well.
population agglomeration scenario also affects the drainage system very much.
So, we have a clear idea about the population in 10 years interval. So, we can
get the data of past population from CMC and predict the future population.
From this data’s we can design a long-lasting drainage system.
in SWMM for modelling
model using SWMM urban drainage cycle the watershed is know we must follow this
method. For that we must design pre-and post-model using this software to
verify the applicability of SWMM software to natural watershed condition.(Burger, Sitzenfrei, Kleidorfer, & Rauch, 2014)
modelling study we have to get the data from experimental study known as
Seolma-cheon watershed. And, other two international studies Weecheon and
Pyungchang. For all this study we must input the area, channel length,
watersheds slope, channel slope. From these parameters we can clearly model the
existing condition and future condition very economically.(Rathnayake, 2015)
software modelling run off simulation needed for pre-and post-models’ needed
substantial parameters for the design. The land use type is also important
parameter for determine run off discharge and the sub catchment properties,
depression storage for pervious and impervious storages manning N value for
overland flow pervious and impervious surfaces, hydraulic conductivity of
impervious surface and soil infiltration parameters. We must adjust all the
parameters according to the SWMM manual.
Figure?3 SWMM Drainage System Model(Rossman, 2015)
Figure -3 which
should be modelled using SWMM. this system shows that S1, S2, S3 are the sub
catchment areas, C1, C2, C3,C4 are storm sewer conduits,J1,J2,J3,J4 are conduit junctions .the system discharges
at the creek point labeled Out1.(Rossman, 2015)
must input the sub catchment parameters area, width, %slope, %impervious,
N-impervious, D-store-Impervious, D-store-perv, %Zero impervious, Method of
Analysis, Suction head, Conductivity, Initial Deflect.(Rossman, 2015)
have to input nodes data’s as well node invert, note max depth, node ponded
area, conduit length, conduit geometry, conduit roughness, flow units, link
offsets, routing model.
above parameters to the above model then we have to run and find out the
difficulties in existing model and what parameters we have to make the change
like wise we can modify the model and come to the perfect drainage system.
catchment is the basic unit for hydrological model. To model pre-development
conditions sub catchments were introduced based on the digital elevation model.
expected substantially alter the surface hydrological patterns and also sub
catchment further subdivided based on surface types and land use parameters.
planned road network the road width, slope, and cross-sectional shape also
important in surface routing and surface drainage water model also should be
developed along the road depend on the conditions.
analyzing this Kelaniya area we have the data of contours, spot heights,
building roads, culvert locations and existing stream line. Then only the
software we can analyze the land profile area which should be quiet enough to
runoff or it should be modified depending of the data which we have. The
culvert designing also important parameters designing the drainage system
because the road is divided the area in to two different zones. Culvert is the
only one connecting both sides. The runoff capacity can manage by the culverts
when flooding occurs. So, we must analyze the existing drainage capacity is
enough to withstand the future condition or it should be increases further.so
we have design the culvert capacity using SWMM software.(Kong et al., 2017)
of building also another main aspect causes this flooding.in now a day’s
conditions ground reality the urban dwellers modify the stream to accommodate
for their land or housing complex. If the land cluster information did not
match with the digital map information. The stream network is modified in
certain lands.so in order to overcome this issue we have to have a proper urban
planning. If it is carried out properly we can avoid the effect of
To stop the
solid waste deposited in the drainage channels we must maintain a proper
disposal method regularly. collect the solid waste regularly to from the
residential and commercial areas in a
systematic manner.as well as separate the solid waste in to different category
then only it can be recycled or dispose. Otherwise we can input the sensors for
the garbage disposal drum to identify the garbage disposal to take the garbage.
This leads to keep the city clean and as well as maintain the drainage path
we have to implement the new methods for disposal of garbage and maintain a
good drainage path and effective drainage system without any disturbances.
drainage system cannot handle the runoff fully. So, we need to modify the
existing one for the efficiency of the flow run off in future. The old drainage
system and retention system accommodate the less than 50% of the total runoff.
But natural retention system of the Colombo city cannot handle 50% of total
runoff. So this shows that we cannot change natural retention system we have to
do modification in the existing drainage or design the new economical drainage
system to accommodate present and future flooding in Colombo city.(Dong, Guo, & Zeng, 2017)
will increase the hydraulic capacity of urban drainage system. And give support
to storm flood management, hydro catchment management, and low-lying area
management.it also give ways to policy guideline for the urban drainage system.
Flood management consist of solid waste management as well. The reason is it
should give a proper functioning of channels. Therefore, it links between both
flood management and solid waste management.
software is very useful because we can design the new drainage system by
modelling the past system of the existing data’s. it is freely available so
that our design become more creative and economical.
from this software we can have a very good drainage system for the Kelaniya
area as soon as finish my research not only that I can have a topographical map
of existing surface. but that is little change due to soil erosion and
incorporation of building. That effect also finally identified and give the solution.
so final output of this research is very helpful for the nations and the people.
From this new drainage system people can live a calm live when the rainfall in
changing due to natural activities.
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