REDESIGNING OF STORMWATER DRAINS LEADING
TO KUKKARAHALLI LAKE AND SUGGESTING
MITIGATIVE MEASURES - A CASE STUDY
Nisha.S, Mamatha A.S. and Pavithra.M.
Department of Environmental Engineering,
Sri Jayachamarajendra College of Engineering, Mysore-570 006, Karnataka, India
Phone: 0821-410693
E-mail: twitterin@yahoo.co.uk
Stormwater drains are designed mainly to control the quantity,
quality of runoff, resulting from storm events. Stormwater drains are also
designed for erosion control, boosting of
natural ground water table,
prevention of eutrophcation and safeguarding other aquatic bodies's life,
enrichment of fresh water resources, maintenance of hygiene and aesthetic
appeal of the lake.
In order to achieve the above goals ,a detailed study of the existing
stormwater drains leading to kukkkarahalli lake was carried out and it was
found that 3 out of the 4 drains required redesigning. The catchment area
was divided into 3 subcatchements, district A, district B and district C
having an area of 37.5 ha, 75 ha and 75 ha respectively. The peak
discharge was found to be 8.43 cum,16.87cum and 16.87cum respectively.
The depth of flow was calculated and was found that all the drains A, B and
C had sufficient depth to carry the discharge, whereas drain D was short by
0.82 m. Hence redesigning is done to increase the total depth of the drain.
Next, it was observed that the actual shape of the drain was not maintained
due to erosion. It was found that drain A was compeletely distorted for about
a length of 315 m, and drain B had lost its shape at different chainages.
Hence by retaining the bedwidth and side slope the same as that existing,
redesigning with respect to earth filling and earth cutting was done as per the
redesigned data. As the result of redesigning, an additional flow of 15 cum
can be allowed into the lake along with the present inflow ,which helps to
increase the fresh water inflow to the lake.
INTRODUCTION
“The natural or man made channels that carry stormwater are referred
to as stormwater drain”[1].
Stormwater drains are designed to control the quality, quantity, timing and
distribution of runoff resulting from storm events. If these drains are
designed properly and modified suitably for the local hydrological scenario,
maximum benefits could be obtained like enrichment of fresh water
resource, improvement of ground water table, improvement of aesthetics of
town or city ,facilitating the safety of adjoining structure of stormwater
drains in the catchment area.
Keeping the above points in mind, a case study of stormwater drains
connecting to Kukkarahalli Lake in Mysore city has been undertaken.
For this purpose, the data including rainfall and topographical data
were collected . Other field data was collected by site surveying.
Objectives of the Study
1. To study the fate of existing stormwater drains leading to
Kukkarahalli lake.
2. To redesign stormwater drains for channelising the storm runoff
into the lake.
3. To estimate the probable financial requirement for rehabilitation of
the drains.
4. To suggest mitigative measures for the management of stormwater
drains.
DESCRIPTION OF THE STUDY AREA AND METHODOLOGY.
The garden city, Mysore is one of the historical places in Karnataka. It
is situated at a latitude of 120 30' N and a longitude of 760 37' 5" E. Tourism
is the major source of income to the city. Some of the major attractions
contributing to its charm are the scenic lakes like Kukkarahalli, Karanji,
Lingambudi, Dalvoi and Devanoor lake, Palaces and Chamundi Hills.
Kukkarahalli lake is situated in a peaceful and scenic atmosphere close to
the Mysore University. It was built by Dewan Poornaiah in 1867.
Unfortunately the beautiful water body has slowly deteriorated. Excessive
inflow of sewage and sludge has resulted in the over nourishment or
eutrophication of this historic and beautiful lake. The exact location along
with the catchment is shown in Figure 1. For the purpose of stormwater
drainage studies, the catchment area of Kukkarahalli lake is divided into
three subcatchments namely District A containing 1 drain, District B
containing 2 drains and District C containing 1 drain. Here drains of width
greater than 1m only are considered.
FIGURE 1 Location And Catchment of Kukkarahalli Lake.
Discharge Estimation
Rational method, is the most widely used peak runoff method in urban
hydrology. A large number of municipalities and local utilities use the
rational formula to design stormwater networks. The rational formula relates
the peak discharge to the rainfall and topographic characteristics of the
drainage area. The primary attraction of the rational formula is its simplicity.
However its drawbacks relate primarily to the fact that the intensityduration-frequency relationships on which it is based were originally
intended for the calculation of a peak-flow rate and not for the calculation
of either the runoff hydrographs or flow volumes [3]. The peak flow at any
given point in drainage system is estimated using following formula.
Q=CAR/360
…………… Equation 1
Where Q = Peak, runoff in m3/s
C = Runoff coefficient
A = Catchment area in hectares
R = Rainfall intensity in mm/hour
Use of Rational method is not recommended in any catchment where
ponding of stormwater might affect the peak discharge. The runoff
coefficients used for different types of drainage area were taken from [2].
Manning’s equation was used to calculate the velocity and water depths in
the drains as described in [4].
Table 1
Existing Conditions of Drain - A
Location – Gangothri Campus
Drain
Type
Total
Chainage
Bed
Total
Lengt
From To
Width
Depth
Longitudi
Side Peak
h (m)
(m)
(m)
(m)
nal
Slop Flow
Slope
e
(m3/s)
0.050
1:1.
16.87
0
(m)
200
6.5
1.63
Trapezoi 400
dal
5
200
400
18
It is a 0.034
-
16.87
flat
terrain
TABLE .2
EXISTING CONDITIONS OF DRAIN - B
Location – Gangothri Layout
Drain
Total
Chainage
Bed
Total
Type
Lengt
From To
Width
Depth
Longitudi
Side Peak
h (m)
(m)
(m)
(m)
nal
Slop Flow
Slope
e
(m3/s)
0.034
1:1.
16.87
0
(m)
200
20.1
3.8
5
Trapezoi 960
dal
200
400
8.2
3.8
0.038
1:1.
5
16.87
400
600
7.5
3.8
0.033
1:1.
16.87
5
600
800
7.5
3.8
0.033
1:1.
16.87
5
800
100
30
3.8
0.031
0
1:1.
16.87
5
TABLE 3
EXISTING CONDITIONS OF DRAIN - C
Location – Open University Campus Gangothri
Drain
Total
Chainage
Bed
Total
Type
Lengt
From To
Width
Depth
Longitudi
Side Peak
h (m)
(m)
(m)
(m)
nal
Slop Flow
Slope
e
(m3/s)
0.014
1:1.
8.43
0
(m)
200
6.4
3.4
Trapezoi 592
dal
5
200
400
6.4
3.4
0.0138
1:1.
8.43
5
400
600
6.4
3.4
0.0133
1:1.
5
TABLE 4
EXISTING CONDITIONS OF DRAIN – D
Location - Paduvarahalli
8.43
Drain
Total
Chainage
Bed
Total
Type
Lengt
From To
Width
Depth
Longitudi
Side Peak
h (m)
(m)
(m)
(m)
nal
Slop Flow
Slope
e
(m3/s)
Rectangu
lar
576
(m)
0
200
1.5
0.7
0.0065
0
16.87
200
400
2
0.7
0.0071
0
16.87
400
600
2
0.7
0.0076
0
16.87
Existing Drainage Conditions
Detailed study of drains at different chainages is shown in Tables 2.1
to 2.4. Survey carried out revealed that two of the drains are heavily silted
and weeded. This has reduced the discharge capacity of the drains
considerably. The drains were also found to be carrying sewage and sludge
flow thereby increasing the quantity of flow in the drain. The major
bottlenecks observed which obstructed the smooth functioning of
stormwater drains were :
 Silting and weeding of drains
 Partial and haphazard lining of drains.
 Flow of sewage and disposal of solid waste into the drains.
 Silting and blockage of tertiary drains.
 Encroachment of flow channels.
the
 Lack of adequate maintenance of the channels and associated structures
like culverts.
 Dumping of construction spills and other materials into the drains.
 Blockage of the drains due to electric poles and stones being used to
cross the drains.
RESULTS AND REDESIGNING OF STORMWATER DRAINS
After the field analysis of present stormwater drain conditions, it was
observed that the drain C is properly designed for peak discharge but drain
A, drain B and drain D required redesigning. Table 5 shows the redesigned
details.
TABLE 5
SUMMARY OF REDESIGNED DETAILS OF DRAINS
Drain
Type
Drain
Total
Peak
Bed
Total
Side
Longitudina
Length
Discharge
Width
Depth
Slope
l Slope
(m)
(m3/s)
(m)
(m)
400
21
6.5
0.86
1:1.5
0.042
960
21
20.1
0.68
1:1.5
0.034
576
21
2
1.52
1:1.5
0.007
A
Drain B
Drain D
Cost Estimation
The major factor, which is to be considered in the redesigning aspect
is to estimate the cost for rehabilitating the entire drain area. Table 6 gives
the unit cost and the total cost for the reconstruction of the drains. Unit
rates have been collected from M/s Dalal Consultancy, Mysore[5].
TABLE 6
COST
ESTIMATION
FOR
RECONSTRUCTION
OF
STORMWATER DRAINS
Sl
Item
Unit
Quantity
N
Rate/Unit Cost
(Rs)
(Rs)
Remarks
o
1
Desilting
cum
300.66
46
13830.36
For 509 m length
2
Deweeding
sq.m
3538.5
2
7077.00
For 824 m length
3
Lining
cum
49.2
1800
808560
For 290 m length
4
Revetment
cum
107.49
260
27947.4
For 1275 m length
5
Earth Cutting
cum
14167.5
72
1020060
For 800 m length
6
Filling
11855.35
34
403081.9
For 475 m length
and cum
Compacting
Total
CONCLUSIONS AND RECOMMENDATIONS
22,66,726.3
Conclusions
 The present condition of the stormwater drains leading to
Kukkarahalli lake were found to be silted, weeded, blocked
with construction debris and polluted by the entry of sewage at
few places.
 The reasons for the above condition of these drains were
mismanagement and improper usage of stormwater drains.
 .In order to facilitate the easy flow through the drain, redesigning
was done to improve the Lake water quality.
 The total cost of remodelling for all the drains worked out to be
around Rs. 23 lakh.
 After remodelling there is an additional inflow of 15 m3/sec
along with present discharge thereby increasing the fresh water
quantity in the lake.
Recommendations
 Necessity of Cleaning
The system should be periodically inspected and cleaned. Better
maintenance includes removing blockages, cleaning catch basins and
repairing where necessary. Pre-monsoon cleaning up of the storm water
system is very important in order to ensure efficient functioning of the
system during rainy days.
 Role of Authorities Concerned
In order to achieve better maintenance of the storm water drainage
system, the following actions have to be taken, so that the drainage system
meets the desired goals.
 Prevent flow of sewage and disposal of solid wastes into drains.
 Prevent silting, weeding and blockage of tertiary drains.
 Prevent encroachments of flow channels and tanks.
 Proper maintenance
of
channel and associated structures (eg.
culverts).
 Prevent dumping of construction spills (debris) and other materials into
drains.
REFERENCES
1. David A. Chin, 2000, " Water Resources Engineering". Prentice
Hall.
2. Warren Viessman, Mark J. Hammer, 1992, " Water Supply and
Pollution Control", 5th Edition, Harper
Collins College
Publishers.
3. Chance Constrained Model For Stormwater System Design and
Rehabilitation “Journal of Water
Resources Planning and
Management”,1997,ASCE..
4. Ven
Te
Chow
,”OpenChannel
Hydraulics”,International
Students,Edition,Mc Graw Hll Publications.
5. Master Plan of Remodelling of Stormwater Drains ,2000 - A
report, Dalal Consultancy.