A Study on Storm Water Drainage System of Annanagara and Ashokanagara of Shimoga City Karnataka India

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1 A Study on Storm Water Drainage System of Annanagara and Ashokanagara of Shimoga City Karnataka India Veena D Savanth Lecturer, Department of Civil Engineering Jain Institute of Technology, Davanagere, Karnataka, India A V Shivapur Professor and Head Department of Civil Engineering, Center for PG studies Visvesvaraya Technological University, Belgaum, Karnataka, India Arun Kumar G S Assistant Professor, Department of Civil Engineering Jain Institute of Technology, Davanagere, Karnataka, India Abstract- The pervious soil is being covered with impervious material by 20 % annually due to ever demanding requirement of shelter for the human settlement. Attempt on Assesment of vulnerability to urban flood has been made to estimate discharge rate based on previous year s rainfall data of AnnaNagar and AshokaNagar of Shimoga city by the authors. The Intensity-Duration-Frequency IDF curves and their equations have been developed for 3h duration storm and cyclones. Keywords Rainfall, Intensity, Runoff, Flood, IDF Curve, Storm Drain. I.INTRODUCTION Precipitation which is overwhelmingly depended on time and space, these two components on which the enormity of precipitation varies. Shimoga is one of the fastest growing city in malnad area which expanding more hugeness of the urban surge occured in the months of June to September. In 2009 a generous cylonic effect on the city especially the study area which is closer to the vehicle terminal and other open amenties influenced, more than 589 houses were impacted and proceeded in the investigation region. STUDY AREA Shimoga lies in the western part of the Karnataka state (India) between to north latitude and to east longitudes covering an area of sq. km. The districts it is surrounded by are Uttara- Kannada and Dharwad in the North, Udupi and Chikmagalur districts in South and Davanagere district in the East. Generally, the weather is hot and humid in the eastern part and very pleasant in the remaining part of the area. It has tropical climate all year. The relative humidity ranges from 27 to 88%, the wind speed recorded is between 4 and 7 Km/hr. Fig 1 shows the study area i.e., Anna Nagar and Ashoka Nagar of Shimoga city. Which covers an area of sq..m. which lies in north and east at 584m above MSL. SOIL TYPE The soils that exist in the study area are reddish to brownish clayey loam to lateritic. The thickness varies from few cm to 3.50 m. The rate of water infiltration through these soils is recorded as 4.3 to 40.11cm/hr. The mixed soil occurs in the areas where the schistose rock is predominant. It is of medium to fine-grained and permeable with higher moisture content. The thickness of soil ranges from 0.5 m to29 m and is having the water infiltration capacity of about 0.60 cm/hour. Volume 5 Issue 3 June ISSN:

2 RAINFALL PATTERN The area enjoys tropical climate throughout the year. Generally, the weather is hot and humid in the eastern part and very pleasant in the remaining parts of the area. The relative humidity ranges from 27 to 88%, the wind speed recorded is between 4 and 7km/hr. The evapo-transpiration is normally high in ghat section as compared to plain in the east. Summer prevails between March to early June, the wet months start from early June to September, October and November months experience scanty rain by N-E monsoon. The winter commences in mid- November and ends in the middle of February. The rainfall data (Automatic Rain Gauge ARG ) for Shimoga city is available for 13 years only ( ) the average annual rainfall is around 1068 mm (for about 10 years). The rainfall pattern suggests a steady decline in rainfall as we move from West to East. The mean pre monsoon rainfall 159 mm, mean South West monsoon rainfall is around 722 mm and North East monsoon season is around 186 mm. The intensity of rainfall is the rate of precipitation per unit time. It can be expressed as either instantaneous intensity or average intensity over the duration of rainfall. The frequency is expressed in terms of return period (T) which is the average length of time between rainfall events that is equaled or exceeded the given (design) magnitude. The average intensity commonly used. Where: P is the rainfall depth, t is the duration of rainfall Figure 1. Study Area [2] Development of IDF Curves II METHODOLOGY From the previous precipitation information the traditional storm happens just for few hours however the precipitation continues for twelve hours or perhaps up to twenty four hours, differentiated because the traditional precipitation and cyclone. Mathematically, before differentiating we have a tendency to premeditated the curve mingling all the three hour period storms in one graph there we have a tendency to didn t got the IDF curves parallel to every different when separating the cyclone and traditional storm then the IDF curves are derived as below and that are nearly parallel to every different within the case of traditional precipitation and cyclone. Case 1: For Normal Rainfall The intensity rainfall data collected for 13 years has been used for the analysis. The frequency analysis has been done to estimeate the storm corresponding to the return period. The intensity duration frequeny curves were developed to know the relationship between storm and period. The durations of rainfall considered for 3-hour. Return periods is calculated for: 2-year, 5-year, 10-year, 20-year, 50-year and 100-year. The mean and standard deviation for the selected durations is calculated. The frequency factor is calculated for all the selected return periods, based on the selected distribution [3]. The rainfall intensity is obtained by the below equation. Volume 5 Issue 3 June ISSN:

3 Where: = mean, S= standard deviation and K T = frequency factor for return period. Table-1 Depth and cumulative rainfall with intensity of ranking for 3 hour duration. Cumulative Depth of rainfall Rank in M Year Depth of rainfall Intensity in mm/hr 01 hr 02 hr 03 hr 01 hr 02 hr 03 hr 01 hr 02 hr 03 hr 2001 October June October August April April October April October June October April May Figure 2. IDF Curve for Normal Rainfall Table- 2 Return period (T r ) and probability of occurrence of the rainfall intensity (F r ) in mm/h Year/ Storm Duration hr 02 hr 03 hr M T r Probability F r & , 2002, 2006 & & Volume 5 Issue 3 June ISSN:

4 Table-3 Intensity of rainfall for different recurrence intervals and given time period from graph and equation. Time period (T) Rainfall intensity By Equation By Graph Case II: For Cyclone For the development of IDF curves, the greatest precipitation profundity of distinctive years which constant for 3 hours of specific year is picked as demonstrated in the table beneath for the cyclone. Table-4 Depth and cumulative rainfall with intensity of ranking for 3 hour duration. Depth of rainfall Cumulative Depth of rainfall Intensity in mm/hr Rank Year in M 01 hr 02 hr 03 hr 01 hr 02 hr 03 hr 01 hr 02 hr 03 hr 2001 October June October August April April October April October June October April May Figure 3. IDF Curve for Cyclone Volume 5 Issue 3 June ISSN:

5 Table-5 Return period (Tr) and probability of occurrence of the rainfall intensity (Fr) in mm/hr Rainfall intensity Year 01 hr 02 hr 03 hr M T r F r , 2010 & & Table-6 Intensity of rainfall for a desired recurrence interval and given time duration from graph and equation. Time period (T) Rainfall Intensity in mm/h By Equation By Graph Storm Discharge Estimation The storm discharge is estimated here using a Rational Formula Q=C*i*A Where, Q= discharge in m 3 /sec, C= runoff coefficient (0.65), i = intensity of rainfall for 1 hr duration and A= Study area in m 2. From the substitution in the rational formulae the discharge will be cumecs for normal rainfall and 3.38 cumecs for cyclone, required dimensions for storm drain is of about d= m and b=1.20 m (rectangular cross section without considering grit). Hyetograph The variation of rainfall with respect to time is shown graphically by hyetograph. For the estimated discharge of 3.38 cumecs considering probability of occurrence 70%, the return period is determined as 1.3 years. K t value of 1.3 year is For 1 hour, 2 hour, 3 hour duration the designed intensities are mm/ hr, 9.94 mm/hr and 6.4 mm/hr Table-7 Details of intensities for 1hr, 2hr & 3hr Storm Duration 1h 2h 3h Rainfall Intensity mm/hr Volume 5 Issue 3 June ISSN:

6 Figure 4. Showing details of hyetograph Infiltration capacity of the soil for the research are ( ) is 6 mm/hr [1]. Figure 5. Showing details of hyetograph for infiltration capacity of soil III. CONCLUSIONS Based on the study the following conclusions are drawn: It has been observed that cyclones are more frequent for the Study area. The observed maximum intensity of normal rainfall is 9.06 mm/hr and for cyclone 16 mm/hr, considering the probability of occurrence 70 % of the return period will be 1.3 years. The runoff discharge for the present storm drainage is 1.62 m 3 /sec. The existing storm drainage size found to be d= 0.9 m b=1.20 m The storm drainage required for the obtained runoff discharge is d= m b=1.20 m, which is Sufficient to carry the present discharge. Volume 5 Issue 3 June ISSN:

7 REFERENCES [1] Government of India, ministry of water resources central ground water board (CGWB). [2] IN&dg=dbrw&newdg=1 [3] P P Mujumdar,Department of Civil Engineering, Lecturer 29, STOCHASTIC HYDROLOGY IISC [4] [5] [6] [7] Khalid K. Al-anazi, Dr. Ibrahim H. El-Sebaie Development of intensity-duration-frequency relationships for the area, International journal on computational engineering research, Vol. 03\Issue, 10, page no Khalid K. Al-anazi, Dr. Ibrahim H. El-Sebaie Development of intensity-duration-frequency relationships for the area, International journal on computational engineering research, Vol. 03\Issue, 10, page no S.De Toffol, A.N.Laghari and WmRauch presented a paper on the analysis of trends in rainfall patterns relevant to urban drainage systems, 11 th International conference on urban drainage, page no Antigha R.E,Ogarekpe N.M. Development of Intensity Duration Frequency Curves for Calabar Metropolis, South- South, Nigeria The International Journal Of Engineering And Science (Ijes),Volum 2,Issue 3,Pages39 42 Volume 5 Issue 3 June ISSN: