Abstract
Urbanization of an area cause to increase the impervious areas in the vicinity of city area that cause to decrease the infiltration and increase the surface runoff. This cause flash floods in low land land areas. areas. Theref Therefore ore stormw stormwater ater manage managemen mentt in urban urban areas areas shoul should d be done done with with sufficient attention. Stormwater drainage problem in Matara Municipality area has become a major problem. This is mainly because of improper practices adopted while developments are taking place. In this cont contex extt alter alterna nati tion on made made to the the surf surface ace topo topogr grap aphy hy and and perm permeab eabil ilit ity y in
prop propert erty y
developmen developments ts have created a significant significant impact impact on increasing increasing the surface run-off run-off rates and volume. People who live in the close proximity, change the topography to prevent the surface runoff runoff throug through h their their land, land, thus, thus, effecti effectivel vely y changi changing ng the natura naturall draina drainage ge paths paths in the urbanized areas. This studies mainly focused to develop a stormwater model for Piladuwa area in Matara municipal council, by the use of EPA SWMM model.
Acknowledgements
First and foremost, I would like to express my appreciation to Prof. N. T. S Wijesekera [Final year year Researc Research h Projec Projectt coordi coordinat nator or and my indivi individua duall Resear Research ch Project Project superv superviso isor], r], for sacrifi sacrificin cing g his priceless priceless time of heavil heavily y loaded loaded work work schedu schedule le in order order to guide, guide, direct direct,, advise, comment, correct and criticize me and my research work. Also there was excellent support from academic staff of the Department of Civil Engineering University of Moratuwa. I make this an opportunity to extend my humble gratitude to all the academic staff members in the Department of Civil Engineering. Special appreciation goes to Mr.Dulanjan Wijesinghe and, Miss.Nimmi sooriyabandara for helping us in GPS survey . I wou would also also like like to than thank k my rese resear arch ch grou roup membe embers rs Mis Miss.H. s.H.M. M.D. D.Ha Hars rsh hani, ani, Miss.K.S.S.Chandrasiri and my batch mates that I closely worked with during the research
Table of Contents
Abstract............................................ Abstract................................................................... .............................................. ................................................................... ............................................ .i Acknowledgements................................ Acknowledgements......... .............................................. .............................................. .............................................. .................................... ...............ii ..ii List of Figures...................................... Figures............................................................. .............................................. .......................................................... ................................... ....vi List of Tables........................................ Tables............................................................... .............................................. ............................................ .................................. ................vii ...vii CHAPTER 01..................................... 01............................................................ .............................................. .............................................. ................................1 .........1 1.1 Introduction...................... ............................................. .............................................. ................................................................ ......................................... ........ 1 1.1.1 Resear Research ch backgrou background nd........ ................ ................. ................. ................ ................ ................ ................ ................ ............... ........... ........ ........ ........ .... 1 1.2 Scope .................... ........................................... .............................................. .............................................. ............................................... ..................................... ...............2 1.3 Objectives..................................... ............................................................ .............................................. ............................................................. ......................................2 1.3.1 Overall objectives of group..................... ............................................ .............................................. ............................................ ..................... 2 1.3.2 Specific objective..................... ............................................ .............................................. .............................................. .................................... ............. 2 1.3.3 Limitation and boundary of the research project..................... ..................................................... .................................. ..2
3.3.2 Area..................... ............................................ .............................................. .............................................. ..................................................... .............................. 19 3.3.3 Width........................................................... .................................................................................. .............................................. ..................................... .............. 19 3.3.4 Manning roughness:........................ ............................................... .............................................. ................................................. .......................... 19 3.3.5 Percentage of pervious and imperviousness ............................................... .......................................................... ........... 19 3.4 Field work execution....................... .............................................. .............................................. .............................................. ............................. ...... 20 3.4.1 Other required data ....................... .............................................. ................................................................ ......................................... ......... 21 CHAPTER 04....................................... 04.............................................................. .............................................. .............................................. ......................................22 ...............22 4.0 Modeling....................... .............................................. .............................................. .............................................. ................................................. .......................... 22 4.1 Model selection..................... ............................................ .............................................. .............................................. ...................................... ................. 22 4.2 My study area.................... ........................................... .............................................. ................................................................ ......................................... ..... 22 4.3.1 Schematic diagram for SWMM model....................... .............................................. ................................................ ......................... 23 4.3.3 Notations & symbols used ...................... ............................................. ............................................................. ...................................... ... 24 4.2.3 Data for model....................... .............................................. .............................................. ............................................... ................................... ........... 24 4.4.4 Design rainfall ra infall intensity...................... ............................................. .............................................. ................................................ ......................... 26 4.4.5 Input rainfall data...................... ............................................. .............................................. ...................................................... ............................... 27
6.3 Sensitivity analysis for other subcatchment ..................... ........................................................... ...................................... ....... 40 CHPATER 07 .............................................. ..................................................................... .............................................. .............................................. ..............................41 .......41 7.1 Conclusion & Discussion..................... ............................................ .............................................. .................................. ........................ ................ ... 41 8.0REFERENCES..................................................................................................................viii 9.0 ANNEXES................................. ANNEXES........................................................ .............................................. .............................................. ....................................... .................viii .viii 9.1 Annex A...................... ............................................. .............................................. .............................................. .................................... .......................... ............... .. viii viii 9.2 Annex B..................... ............................................ .............................................. .............................................. ....................................................... ................................ ix
List of Figures
Figure 1 – Matara Municipal Council area................................................................................1 Figure 2 – Flood hazards
................................................................................................2
Figure 3 - Catchment areas.........................................................................................................3 Figure 4 - Methodology flow chart........................................................................................ ....4 Figure 5 - Surface runoff reducing ......................................................................................14 Figure 6 -Pervious cathbasin
........................................................................................15
Figure 7 - sMap of selected area (Piladuwa)...........................................................................23 Figure 8 - Divided subcatchments..........................................................................................23 Figure 9- SWMM model schematic diagram...........................................................................24 Figure 10 notation used for SWMM................................................................................ .24 Figure 11 - Input parameters for the model..............................................................................25 Figure 12- manning’s roughness values..........................
25
List of Tables
Table 1 - Model comparison....................................................................................................11 Table 2 - Model comparison.................................................................................................11 Table 3 – Field work execution ..............................................................................................21 Table 4 – Catchment details ....................................................................................................29 Table 5 – Subcatchment Details...............................................................................................29 Table 6 - Subcacthment Runoff............................................................................................33 Table 7 - Maximum node depth ..........................................................................................33 Table 8 - Node inflow summary.......................................................................................34 Table 9 - Node flooding summary...........................................................................................34 Table 10 - Outfall Loading Summary................................................................................. .35 Table 11 - Link flow summary..............................................................................................35 Table 12 – Flooding nodes.......................................................................................................37
CHAPTER 01 1.1
Introduction
1.1.1
Research background
When the history is considered, it can clearly see that the civilization has occurred around the f flood plains. Matara Municipal Council Area is also situated in a flood plain of Nilwala River (Figure 1) and has experiencing stormwater drainage problems,such as flash floods.
Figure 2 – Flood hazards
1.2
Scope
The main scope of this study is to develop a mathematical model for the Matara Municipal Council Area, to provide engineering and management options to mitigate the stormwater problem. 1.3 1.3.1
Objectives Overall objectives of group
1.4
Study area
Matara is located at the Southern coast of Sri Lanka. Matara is a well developed commercial centre. Nilwala River is the main fresh water body at close proximity. In Matara Municipal area there are three sample areas which were identified for detailed modeling. They are listed below. 1. Piladuwa 2. Walgama 3. Thotamuna
Figure 3 - Catchment areas
1.5
Study Methodology Flow Chart
1.6
Activities Executed
Literature survey
Literature surveys done to identify best software package to this project and also to gain knowledge what have done by other have done relating to our research project. Literature survey is very important to find manning’s roughness value, parameters for GREEN AMPT infiltration method etc….
GPS practice
To take the GPS point, photo point and voice cut at the field. GPS points are very important to identify the path of the river , also we can check that if there is a deviation with map also and length between nodes can be measures using GPS points .
Practicing a sample data collection
Before going to the field, it is important to have firsthand experience in how to take the relevant data accurately and quickly. So
Field visit
Field visits were conducted for collect data of the subcatchment such as vegetation, ponded areas, geometry of channel, nodes etc…..
Data arranging and summarizing
After every field visit it was necessary to arrange and summarize the collected data for future references.
Even though we develop a computer model e can’t guarantee that it would give accurate result as output . To assure reliable output from the model it is necessary to calibrate the model with the available data for rainfall data and inundation depths.
Sensitivity analysis
Sensitivity analysis is important to identify which parameter affects mostly affect to the outflow from the catchment. After identifying those parameters engineering and management option can be given.
CHAPTER 02 2.1 Literature review 2.1.1 Brief History
It is advisable to discuss the problems of existing Nilwala scheme, which was implemented in 1980 s with technical consultancy of a French company. The strategy of ‘protecting lands by embanking and evacuating storm water by pumping’ was mainly applied in this scheme. Other alternatives such as diversion, storage, temporary detention, enlarging river channel etc were not been considered. Flood warning and bypassing system had been attempted, but failed due to various socio - economic factors. The Nilwala scheme was subjected to many controversies since the beginning. The time allocated for planning and design was very limited. The problem was not discussed widely and the stakeholders and local expertise point of view were not taken in to consideration. The scheme could not achieve the targeted benefits. Specially the first phase of the scheme, Kiralakele, was a complete failure and still abandoned after the several attempts
the water-retaining and evapotranspirating functions of the soil and vegetation in the urban landscape. In an undeveloped area, rainfall typically infiltrates into the ground surface or is evapotranspirated
by
vegetation.
In
the
urban
landscape,
these
processes
of
evapotranspiration and water retention in the soil are diminished, such that stormwater flows rapidly across the land surface and arrives at the stream channel in short, concentrated bursts of high discharge. This transformation of the hydrologic regime is a wholesale reorganization of the processes of runoff generation, and it occurs throughout the developed landscape. When combined with the introduction of pollutant sources that accompany urbanization (such as lawns, motor vehicles, domesticated animals, and industries), these changes in hydrology have led to water quality and habitat degradation in virtually all urban streams. (CLAIRE WELTY, et al., 2008) The influence of humans on the physical and biological systems of the Earth’s surface is not a recent manifestation of modern societies; instead, it is ubiquitous throughout our history. As human populations have grown, so has their footprint, such that between 30 and 50 percent of the Earth’s surface has now been transformed (Vitousek et al., 1997). Most of this land area is not covered with pavement; indeed, less than 10 percent of this transformed surface is truly
present there are few studies on urban flooding that O. Mark et al. / Journal of Hydrology 299 (2004) 284–299 285deal with both the conditions in the surcharged pipe network and the extensive flooding on the catchment surface. Even fewer projects have dealt with modeling urban flooding in developing countries. Some of the few case studies dealing with of modelling of urban flooding which both includes the pipe system and extended surface flooding are: Bangkok (Thailand) (Boonya-Aroonnet et al., 2002); Dhaka City (Bangladesh) (Mark et al., 2001); Fukuoka and Tokyo (Japan) ( Ishikawa et al., 2002); Harris Gully (USA) (Holder et al., 2002); Indore (India) (Kolskyet al., 1999) and Playa de Gandia (Spain) (Tomicˇic´ et al., 1999). These studies treated urban flooding as a one-dimensional (1D) problem. Schmitt et al. (2002) considered a 2D model as a benchmark for 1D model. A model, which dynamically couples a 1D pipe flow model with a 2D hydrodynamic surface flood is currently under development (Alam, 2003).
Many numerical models available today adopt numerical schemes to the solutions of full de Saint-Venant equations. For instance, models like SWMM-EXTRAN ( Huber and Dickinson,
Table 1 - Model comparison
(Review of storm water models
by Christopher zoppou)
SWMM free and it can use for planning and designing urban models.
The storm water
management model(SWMM) was developed for the Environmental
Protection Agency in 1969 – 1971 as a singel event model for simulation of quantity and quality processes in combined sewer systems.It has since been applied to virtually every aspect of urban drainage,from routine drainage design to sophisticated hydraulic analysis to non-point source runoff quality studies, using both single event and continous simulation.Through subdeviding large catchments and flow routing down the drainage system.SWMM can be applied to catchments of almost any size ,from parking lots to subdevision section to cities. (philip B.Bedient, 1992)
The EPA Storm Water Management Model (SWMM) is a dynamic rainfall-runoff simulation model used for single event or long-term (continuous) simulation of runoff quantity and quality from primarily urban areas. The runoff component of SWMM operates on a collection of subcatchment areas that receive precipitation and generate runoff and pollutant loads. The routing portion of SWMM transports this runoff through a system of pipes, channels,
•
Evaluating the effectiveness of Best Management Practices for reducing wet weather pollutant loadings.
2.6 Engineering Guidelines
Detained water contributes to runoff and therefore detention ponds or basins must
have an outlet and outfall system . A gravity outfall should be used whenever feasible. Pumping should only be used where there is no other practical way of handling the excess runoff. (Highway Design Manual )
Detention pond designing
Detention ponds are the most commonly used form of runoff control, Outlet facilities for ponds can consist of a concrete weir, a berm with culverts at several levels, a mid-pond draw-off, or any one of a variety of other outlet structures. Side slopes are typically
stormwater is held, which creates a small permanent wetland. Plants in the wet area hide the sediment and debris accumulated near the outlet. Disadvantages include moderate to high routine maintenance needs, infrequent but expensive sediment removal, and nuisance problems including weeds, odors and debris collection. Dry basins are considered unsightly at least in part because the accumulated sediment and debris are visible between rains.
Surface runoff reducing
On-site (Lot-level) Controls On-site (Lot-level) controls are practices that reduce the quantity of stormwater runoff and improve the water quality before the runoff reaches the conveyance system. These practices are applied at a single lot level or multiple lots in a small area. Reduced Lot Grading The development standards require a minimum lot grade of two per cent to ensure adequate drainage of stormwater away from the buildings. In order to avoid foundation
Pervious Catchbasins
Pervious catchbasins are designed to convey the road drainage and these systems have large sumps that are physically connected to an exfiltration storage medium. The storage medium is located below or beside the catchbasin. Pervious catchbasin details for road drainage are shown in Figure6
CHAPTER 03 3.1 Data Collection 3.1.1 General description
Field visits conducted to collect subcathment parameters such as vegetation, ponded areas, geometry of channel, nodes etc….. These field-collected data are very important for model calibration and verification in case of ungauged catchments. SWMM software was practiced before the field visit to familiarize with the input parameters. Before going to the field locations in Matara, a preliminary field visit was conducted at Molpe- Katubedda area to gain experience on field parameter capturing. Also a GPS survey was done in the university premises to familiarize with the instruments. It is important to know about parameters that must be collected at the field for model development. For model calibration and verification purpose at least the upper limit and the lower limits of the water flow in conduits must be known in the case of unavailability of
Canal bank condition(concrete, gabion etc…)
Position of nodes
3.3 Sample calculation
After every field visit desk study was carried out to complete the calculation accordingly. The sub catchments slope, area, width, manning’s roughness and percentage areas of pervious and imperviousness, were calculated using collected data, 1:10,000 topographic sheets, and Arc GIS software. Infiltration model choose for computation was the Green-ampt model. Required data for this method can be found in SWMM help manual, provided the soil type is known. 3.3.1 Slope
If contours are present and we can recognize water flowing paths can be recognized then water path length and contour intervals were measured to calculate the slope.
Considering all, Final Slope = (0.07x516.38+0.044x443.31+0.0896x294.65) 1254.34 =
0.0654
3.3.2 Area
Subcatchments of the study area was divided according to the contour pattern of that area. Using Arc GIS software, areas of each subcatchment were calculated by creating a polygon. 3.3.3
Width
This is given by the subcatchment area divided by the maximum overland flow length. Maximum overland flow length was taken as the length of the water path that starts at the most far end of the sub catchment.
Subroad2
=
Percentage of impervious
=
•
603.3m 2 18027.05 x 100% = 9%
=
200290.8
Marshy land area 1
=
22221.96m2
Marshy land area 2
=
7259.09m2
Areas from trees
=
67263.19m2
Areas for earth soils
=
5169 m2
Percentage N pervious
N values for short grass
=
0.15
used a float and found the flow velocity of the water. Also got GPS point of the path. From the peoples asked about rain and flood height and frequency and maximum flow of canal and minimum flow. 02
Piladuwa
“
04/03/2010 03 04
Thotamuna 13/03/2010
05
“
Thudawa
“
Kunu Ela
“
14/03/2010 06
Brownshill
Table 3 – Field work execution
“
CHAPTER 04 4.0 Modeling 4.1 Model selection
We used EPA SWMM software use to model the catchment in our research work because of the following reasons. 1. SWMM is dynamic rainfall-runoff model used for single event or long term (continuous) simulation of runoff quantity and quality from primarily urban areas. 2. Specially design for urban watersheds. 3. Handles drainage networks of any sizes 4. Accommodates various conduit shapes as well as irregular natural channels
Figure 7 - sMap of selected area (Piladuwa) 4.3.1 Schematic diagram for SWMM model
Figure 9- SWMM model schematic diagram
4.3.3 Notations & symbols used
There are some notations which are used to indicate the symbols in the model. Those notations can be changed by varying the default values of the model. Following are the notations which are used for this study. S – Subcathment C – Conduit (canal) J – Nodes Out – Outfall
Figure 11 - Input parameters for the model
4.4 Input data for the model 4.4.1 Manning’s roughness
Figure 13 –Infiltration data 4.4.3 Depression storage data
Return period In Years
10 X
Zone I Zone 2 Zone 3 Zone 4 Zone 5
25 Y
79.2 109.98 112.7 47.19 32.67
X 0.747 0.837 0.827 0.645 0.684
50 Y
73.75 150.95 146.26 63.26 49.25
X 0.712 0.859 0.844 0.662 0.731
88.91 176.74 167.77 72.08 52.09
According to the map of hydrological stations and Zones Matara is located at zone 3. Then for 10 year return period the Intensity become 0.845 inches/hr.
Figure 16 - Time series
4.4.6 Catchment details
Sub Catchment 10
0.0136
0.26
0.0024
163.3
Sub Catchment 11
0.0426
0.24
0.0026
183.7
Sub Catchment 12
0.0437
0.36
0.0012
110
Sub Catchment 13
0.0394
0.25
0.0025
122.4
Sub Catchment 14
0.0306
0.33
0.007
130.7
Sub Catchment 15
0.0425
0.37
0.009
137.8
Sub Catchment 16
0.0509
0.3
0.002
176.6
Sub Catchment 17
0.053
0.36
0.003
1301.7
Table 4 – Catchment details
Subcatchmen t
NImpervious
N-perv
S- Imperv
S-Perv
%zero
CHAPTER 05 5.0 Model results
After modeling and calibration the mathematical model, it can be use to take number of out puts such as flow simulations, subcathment runoff, infiltration etc. Some results are given below which generate for the Piladuwa (My catchment). 5.1 Surface runoff
5.2 Simulation result Figure 19 – Schematic diagram of Piladuwa
Node9 Node 5 Node6 Node 7 &8
Node depth vs time graph can use to identify that maximum depth of the water level at any node . Figure 22
Node15
Node15
Node15
These animated results shows that this canal in my catchment flooded within 1 st 15 minutes, so this canal system flooded with design rainfall input. 5.3 Subcacthment Runoff summary
5.5 Node inflow summary
Table 8 - Node inflow summary
5.7 Outfall Loading Summary
Table 10 - Outfall Loading Summary
5.8 Link flow summary
From the field data ,calculated data and output from the result following maximum and minimum values can be identify.
Largest subcatchment
=
0.06 km2
Smallest subcatchment
=
0.009 km2
Maximum slope of the catchment
=
0.009 km2
Minimum slope of the catchment
=
0.0004km2
Maximum out flow from the catchment
=
0.249 m3
Minimum out flow from the catchment
=
0.029 m3
Maximum runoff coefficient
=
0.989
Minimum runoff coefficient
=
0.568
CHAPTER 06 6.1 Sensitivity Analysis
At the field we identify the flooding location, from the model we got those area getting flooded, after calibration of the model. These flooding nodes as below:
Flooding Node
Related subcathment
J1
S6
J15
S11
J16
S14
J17
S12
Table 12 – Flooding nodes So it is needed to do a sensitivity analysis for above mentioned subcatchments to identify
Peak
peak runoff%
% slope
% change of slope
0.0025
-50
0.195
4.4
0.005
0
0.204
0
0.0075
50
0.209
2.4
runoff(m 3/s) change
Table 13 - Subcatchment slope vs peak flow
Peak
Peak runoff
Manning's "n"
% change of "n"
0.24
0
0.204
0
0.36
50
0.194
4.9
0.48
100
0.187
8.33
0.8
233
0.176
13.7
runoff(m 3/s) %change
Table 14 - Pervious Manning's n vs. peak out flow
6.3 Sensitivity analysis for other subcatchment
s tl r si s yl a n a y
u s e
CHPATER 07 7.1 Conclusion & Discussion
The output from the SWMM model and field observations are matching so SWMM can use to model this catchment area. In Piladuwa area major problem is blockage of water by the bund which was built under Nilwala scheme. This causes to flooding in the area marked in below figure. Also capacity of this canal is very much low consider to the in flow.
Figure 25 – Flooding area
8.0 REFERENCES •
Philip B.Bedient, W. C. (1992). hydro;ogy and flood plain analysis. addison-wesley .
•
Lewis,A, March 2008 Storm Water Management Model User’s manual Version 5.0, U.S. Environmental Protection Agency, Cincinnati.
•
Ponrajah, A.J.P 1989, Technical Guide Lines for Irrigation Works. 1 st ed. Irrigation Department.
•
Wijesekera,N.T.S 2009, Preparation of the storm water drainage plan fornMatara Municipal Council area, University of Moratuwa, November1998.
•
David, E, Farley.J & Haynes,C Design and routing of storm flows in an urbanized
watershed without surface streams, Journal of Hydrology, Department of Civil and Environmental Engineering, Duke University USA.
•
Mendham, NJ Municipal Options for Storm water Management, ResourcePaper, Association of New Jersey Environmental Commissions.
•
The National Academy of Sciences, 2008, Urban storm water Management in the
Unites states , National Academy of Sciences.
•
Chow, V. T., Maidment, D. R. & Mays, L. W. (1988) Applied Hydrology , New York etc., McGraw-Hill. (0-07-010810-2)
•
Maidment, D.R. 1993, Hand Book of Hydrology. 1st ed. New York: McGraw Hill Book Company.
•
Storm water Drainage manual - Planning, Design and Management, Drainage Service
9.0 ANNEXES 9.1 Annex A
Photos taken at the field
