Environmental Engineering II

Transcription

1 Environmental Engineering II Prof. Rajesh Bhagat Civil Engineering Department Y.C.C.E.,Nagpur B. E. (Civil Engg.) M. Tech. (Enviro. Engg.) GCOE, Amravati VNIT, Nagpur Experience & Achievement: Selected Scientist, NEERI-CSIR, Govt. of India. GATE Qualified Three Times. Selected Junior Engineer, ZP Washim. Three Times Selected as UGC Approved Assistant Professor. Assistant Professor, P.C.E., Nagpur. Assistant Professor, Cummins College of Engg. For Women (MKSSS, Nagpur) Mobile No.: / ID :- rajeysh7bhagat@gmail.com Website:-

2 UNIT-I 1) Systems of sanitation: Conservancy and water carriage system. Patterns of sewage collection systems. 2) Quantity of storm water and sanitary wastewater. 3) Hydraulic Design of sewers - capacity, size, grade, shapes and materials. 2

3 UNIT-II 1) Sewer Appurtenances manholes, street inlets, storm water overflows, inverted siphons, flushing and ventilation. 2) Construction and Maintenance of sewers, equipment s for maintenance & safety equipment s. 3) Sewage pumping. 4) House drainage systems, sanitary fitting and appliances, traps function and types, anti-syphonage, inspection chambers. Storm water drainage. 5) Rain water harvesting for individual houses & Different Methods. 3

4 UNIT-III 1) Characteristics of wastewater. 2) Flow sheet of conventional sewage treatment plant. 3) Preliminary and primary treatment: Screens, Grit chambers, Primary settling tank. Design of bar screens, grit chambers and primary settling tanks. 4

5 UNIT-IV 1) Secondary Treatment: Principle of Biological Treatment. Activated sludge process, Trickling Filter Concept, 2) SD & SDB: Functioning and Basic Load Calculations. Sludge digestion, Sludge drying beds. 3) Methods of disposal: Disposal on land and in water stream. 4) Self-purification capacity of stream. 5

6 UNIT-V 1) Rural sanitation: Pit Privy, Aqua Privy, Bio-gas Recovery, Eco-Sanitation. Septic tank including soak pit. Imhoff tanks. 2) Industrial Waste Water Treatment: Basic concepts of Industrial Waste Water Treatment, flow equalization, neutralization. Common treatment alternatives for industrial waste water. 6

7 UNIT-VI 1) Introduction to Air Pollution, 2) Meteorological Parameters. 3) Monitoring methods. 4) Techniques of air pollution control. 7

8 References:- 1. B.C. Punmia, Waste Water Engineering, Laxmi Publication 2. S.K. Garg, Environmental Engineering Vol II, Standard Publication 3. G.S. Birdie, Water Supply & Sanitary Engineering, Dhanpat Rai Pub Company 4. M.N. Rao & H.V.N. Rao, Air Pollution, McGraw Hill Publication. 5. M.J. Machghee, Water Supply & Sewage, McGraw Hill Publication.

9 Course Objective: 1) To acquaint development of railway transportation in India. 2) To understand geometric design of railway tracks. 3) To know zoning laws for development of air transportation in India. 4) To study tunnel alignment and necessity of tunnels. Course Outcome: 1) An ability to update & upgrade knowledge about transportation system in India. 2) An ability to design railway tracks & crossing. 3) An ability to avail information about development of air transportation in urban areas. 4) An ability to understand the construction of tunnel & advances in tunneling. 9

10 Grading: Grading is based on the following components that are weighted as described below: SN Criteria Distribution of Marks (%) 1 Online Test 4 2 Class Copy / Assignment 4 3 Attendance 2 4 Mid Semester Examinations-I 15 5 Mid Semester Examinations-II 15 6 End Semester Examination 60 10

11 Importance of Sanitation System:- 1) Spent water from bathroom, kitchens, basins, house washing, street washing, from industrial processes, semi liquid waste of human and animal excreta, dry refuse of houses, etc are produced daily. 2) If proper arrangement for collection, treatment & disposal of all waste produced are not made, they will go on accumulating & creates such foul condition that the safety of the structure such as building, roads will be in danger due to accumulation of wastewater in the foundation. 3) The disease producing bacteria spread up in the stagnate water & the health of public will be in danger. 4) All the drinkable water will be polluted. 5) Total insanitary conditions will be developed in the town. 6) It will be impossible for public to live in the cities. 7) Therefore in the interest of community or society it is most essential to collect treat & dispose of all the waste products in such a way that it may not cause any havoc to the people residing in the town. 11

12 Sanitation Work or System:- Sanitary engineering starts at the point where water supply engineering ends. The sanitary works can be broadly classified as: 1) Collection Work 2) Treatment Work 3) Disposal Work Collection Work: Collecting all types of waste products of the town. Refuse is collected separately & sewage is collected separately. Collection work should be such that waste matter can be transported quickly & steadily to the treatment plant. Safe, efficient & economical. 12

13 Treatment Work: Sewage needs treatments before disposal so that it may not pollute the environment and water body. If the wastewater is not treated it will cause many harms like pollution of water supply sources, destruction of food, fish and valuable aquatic life, creation of unpleasant sights & atmospheric air pollution, etc. Disposal Work: The treated or untreated wastewater are disposed off in various ways by irrigating fields or discharging into natural water course, etc. 13

14 Points are to be considered before finalizing a Sanitary Project:- 1) Financial aspects: 2) Population: 3) Quality of sewage: 4) Rainfall: 5) Rate of sewage: 6) Sources of sewage: 7) Topography of area: 8) Present method of disposal: 9) Treatment Methods: 10) Trends of town development: 14

15 Site for Sewage Treatment Works:- 1) Good foundation soil should be available for various units to rest firmly on the ground. 2) The general slope of the site should be moderate, so that flow from one unit to the other take place by gravity only. 3) Site should be lowest level area of the town, so that sewage from entire town can be collected by gravity only. 4) Enough area is available for future expansion. 5) Safe from flood. 6) Site should be situated on the leeward side of wind. 7) Not far way from city. 8) Subsoil water level at the site should be remain low even during monsoon. 15

16 Sewage or Wastewater : 1) Used water or liquid waste generated by the community due to its various activities. 2) Any water or liquid that contains impurities in such a concentration that is harmful if disposed into the environment. 3) It is 99.9% water & 0.1% solids 4) Quantity of sewage = 75 to 80 % of the water supplied 5) Lesser the supply of water greater the strength & vice-versa. 16

17 TYPES OF WASTEWATER DEPENDING ON SOURCE OF GENERATION Domestic wastewater: the used water from the residential, commercial, & institutional zones of a city. partially treated wastewater from small industries are also included Industrial wastewater: the liquid waste from large & medium scale industries. vary in quantity and quality large volume & high strength 17

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19 Collection Methods : 1) Conservancy System 2) Water-Carriage System 19

20 Conservancy System: Prevailing in small town or undeveloped towns. Various types of refuse & storm water are collected, conveyed & disposed off separately by different methods therefore it is called conservancy system. In the past, disposal of waste from water closets was carried out manually (dry System) and wastewater generated from kitchen and bathrooms was allowed to flow along the open drains. Human excreta is collected separately in privies or conservancy latrines. The liquid & semi-liquid waste are collected in separate drains of the same latrines, from where they are removed through human agency. After removal night soil is taken outside the town in closed animal drawn carts or trucks. Cheaper in initial cost. Aesthetic appearance of city can not be increased. 20

21 Water-Carriage System: With the development & advancement, urgent need was felt to replace conservancy system with improved type of system, in which human agency should not be used for the collection & conveyance of the sewage. Water is the cheapest substance used to transport the sewage easily & effectively therefore it is called water-carriage system. Excremental matter are mixed up in large quantity water & are taken out from the city through properly designed sewerage system., where they are disposed off after necessary treatment. Initial cost & maintenance cost is more. 21

22 Water-Carriage System: The old system may pose the health hazards, because of the possibilities of flies and insects transmitting disease germs. This is avoided in new system because of transport of night soil in close conduit. The human excreta is washed away as soon as it is produced, thus storing is not required as required in the old system of manual disposal. In the old system, the wastewater generated from the kitchen and bathrooms was required to be carried through open roadside drains for disposal. This is avoided in sewerage system as the open drains could generate bad odor when used for disposal of organic waste. The water carriage system does not occupy floor area, as the sewers are laid underground. Construction of toilets one above the other is possible in water carriage system and combining latrine and bathrooms together as water closets is possible. 22

23 Advantages of Water-Carriage System: It is hygienic method. No human agency is employed. There is no nuisance & risk of epidemics is less. It occupies less space in crowded lane. Due to more quantity of sewage, self cleansing velocity can be obtained even at less gradient. Building can be designed compact as one unit. Less area is required for disposal. The usual water supply is sufficient & no additional water is required. This system does not depend on manual labor every time. Sewage after proper treatment can be used for various purposes. 23

24 Conservancy System Very cheap in initial cost. Causes nuisance & Foul smell. Aesthetic appearance can not be increased. Large area require for burying excremental matter. Storm water is carried in drains, hence no pumping. Fully dependent on human agency. Does not permit compact design of structure. Disposal without any treatment may pollute the natural water course. Requires small quantity of water. Waste liquid reaching the disposal point is less, hence it can be disposed off without any treatment. Water Carriage System High initial cost. No foul smell. Aesthetic appearance can be increased. Less area is required. May or may not require pumping. No human agency is involved. Permits compact design of structure. Sewage is treated up to required degree of saturation hence less or no pollution. Requires large quantity of water. Large quantity of sewage highly polluted in nature, it requires treatment before disposal.

25 Common Terms Used in Sanitary Engineering: Refuse: Anything rejected or left as worthless. Sullage: Wastewater from bath rooms, kitchens, etc. & does not include human or animal excreta. Sewage: Liquid waste from community & includes sullage, discharge from latrines, urinals, industrial wastewater & storm water. Sanitary Sewage: Liquid waste of domestic & industrial places. Extremely foul in nature & required to be disposed off very carefully. Sewer: Underground conduits or drains through which sewage is conveyed are known as sewers. Sewerage: The entire science of collecting and carrying sewage by water carriage system through sewers is known as sewerage. 25

26 Sewerage System: The sewerage system are classified as follows: 1) Combined System 2) Separate System 3) Partially Separate System Combined system: Only one set of sewers is used to carry both the sanitary & storm water. Most suited in areas having small & evenly distributed rainfall throughout the year. In India, this system will face the problem of maintaining self cleansing velocity in the sewers during dry season. No need of flushing because more self cleansing velocity is available due to more quantity of sewage. Rain water dilutes the sewage. Initial cost is high as compared with separate system. In congested areas, easy to lay one large sewer than two smaller sewers. 26

27 Advantages of Combined System: Where rainfall is spread throughout a year, there is no need of flushing of sewers, as self cleansing velocity will developed due to more quantity because of addition of storm water. Only one set of pipe will be required for house plumbing. In congested areas it is easy to lay only one pipe rather than two pipes as required in other systems. Disadvantages of Combined System: Not suitable for the area with small period of rainfall in a year, because dry weather flow will be small due to which self cleansing velocity may not develop in sewers, resulting in silting. Large flow is required to be treated at sewage treatment plant before disposal, hence resulting in higher capital and operating cost of the treatment plant. When pumping is required this system is uneconomical. During rains overflowing of sewers will spoil or endanger public health

28 Separate System: 1) Two sets of sewers are used, one for carrying sewage & other for carrying storm water. 2) Sewage is carried to the treatment plant & storm water is discharged directly into natural outlet. Advantages: 1) Load on treatment units becomes less. 2) Natural water is not unnecessarily polluted. 3) Small size sewers are required. 4) Storm water discharged into natural streams. 5) Economical when pumping is needed for lifting of sewage. Disadvantages: 1) Cleaning of sewer are difficult as they are small in size. 2) Maintenance cost is high. 3) Self cleansing velocity is not easily achieved due to small quantity of sewage. 28 4) Storm water sewers operates only during monsoon hence becomes dumping place for garbage during summer-winter & may thus be choked. 28

29 Partially Separate System: 1) Part of the storm water especially collected from roofs and paved courtyards of the buildings is admitted in the same sewer along with sewage from residences and institutions, etc. The storm water from the other places is collected separately using separate conduits. Advantages: 1) Economical and reasonable size sewers are required. 2) Work of house plumbing is reduced as rain water from roofs, sullage from baths and kitchen, etc. are combined with discharge from water closets. 3) Flushing of sewers may not be required as small portion of storm water is allowed to enter in sanitary sewage. Disadvantages: 1) The quantity of storm water admitted in sewer may increase the load on pumping and treatment units. 2) Self-cleansing velocity may not develop in the sewers in dry weather

30 Separate System The quantity of sewage is to be treated is very less, because no need to treat the storm water. Combined System Treatment of sewage and storm water are to be done, so it is very costly method. Suitable for places where more intensity of rainfall takes place. Suitable for places where less intensity of rainfall takes place throughout the year. Difficult to use in narrow street. Suitable for narrow street. In case of pumping of sewage, it is less costly. Two sewer line of small size is needed & it is not costly as compare to combined system. Pumping of sewage is costly because sewage is having storm water. Only one line of sewer of big size is required, hence more costly.

31 Patterns of Collection System: 1) Perpendicular Pattern 2) Interceptor Pattern 3) Radial Pattern 4) Fan pattern 5) Zonal Pattern The patterns of collection system depend upon: 1. The topographical and hydrological features of the area. 2. The location and methods of treatment and disposal works. 3. The type of sewerage system employed, and 4. Extent of area to be served. 31

32 1) Perpendicular pattern: The main trunk sewer are laid perpendicular to natural water course. The shortest possible path is maintained for the rains carrying storm water and sewage Suitable for separate system and partially separate system. Not suitable for combined system, because treatment plant is required to be installed at every point of outlet; otherwise it will pollute the water body where the sewage is discharged. Fig. 1.1 Perpendicular Pattern (1) 32 32

33 2) Interceptor pattern: Improvement over the perpendicular pattern. Sewers are intercepted with large size sewers which are laid along the water course. Interceptor carries sewage to a common point, where it can be disposed off with or without treatment. Overflow or Storm regulators may be provided to handle very large flow or storm water. Fig. 1.2 Interceptor Pattern (1) 33

34 3) Radial Pattern: Sewers are laid radially outwards from the centre of city, hence this pattern is called as radial pattern. It is suitable for sewage disposal by land. More number of disposal works is required. Fig. 1.3 Radial Pattern (1) 34

35 4) Fan Pattern: Single treatment plant is located at a certain common point & the entire sewage flow is directed towards this point. Suitable for a city situated at one side of the natural water body, such as river. Number of converging main sewers and sub-mains are used forming a fan shape. The drawback in this pattern is that larger diameter sewer is required near to the treatment plant as entire sewage is collected at common point. For new development of the city the load on existing treatment plant increases hence restriction will have to be imposed on such development.. Fig. 1.4 Fan Pattern (3) 35

36 5) Zone Pattern: City is divided into suitable zones and separate interceptor is provided for each zone. More numbers of interceptors are provided in this pattern. Suitable & economical for sloping area than flat areas. Fig. 1.5 Zone Pattern (3) 36

37 Factors to be Considered in the Determination of the Quantity of Storm Water or Sewage: 1) Intensity & Duration of Rainfall: 2) Topography of Watershed: a) Extent of Catchment Area: b) Shape of the Area: c) Slope of the Area: d) Nature of Soil: e) Number of Available Ditches in the Area: 3) Atmospheric Temperature, Wind & Humidity:

38 Storm Water: The quantity of storm water can be calculated by following two methods Rational & Empirical Formulae: 1) Rational Method: 2) Q = ( C x R x A ) / 360 Where, Q = Quantity of storm water in m 3 /s R = Intensity of rainfall, mm/hour A = Drainage area in hectors C = Runoff coefficient, Overall runoff coefficient for different types of surface area, C = ((A 1 x C 1 + A 2 x C A n x C n ) / (A 1 + A A n )) A 1, A 2, A n are the different area & C 1,C 2, C n are their runoff coeff. Respectively. Que.1 The surface on which the rainfalls occurs consists of roots and pavements 40% (C 1 =0.8), lawn and gardens 60% (C 2 =0.2), calculate the runoff coefficient. If the total area of the district is 2 hectors and the intensity of rainfall is 50mm, what is the rate of runoff of the district. C = (0.32A A ) / A = 0.44 Q = (2 x 0.44 x 50 ) / 360 = m 3 /s

39 Storm Water: The quantity of storm water can be calculated by following two methods Rational & Empirical Formulae: Empirical Formulae Method: All empirical formulae are only applicable under certain condition. Suitable for a particular region after long practical, experience & collection of data. 1) Burkli- Zeiglar Formula: Q = (( C I A)/141.58) 4 (S/A) 2) McMath s Formula: Q = (( C I A)/141.58) 5 (S/A) 3) Fuller s Formula: Q = C M 0.8 / ) Fanning s Formula: Q = 12.8 M 5/8 5) Talbot s Formula: Q = 22.4 M ¼ Q = Runoff in m3/s I = intensity of rainfall, cm/hr ( R = rainfall intensity ) S = slope of the area, meter per thousand meter A = Drainage area in Hectors & M = Drainage area in Km2 C = Runoff coefficient or I = Impermeability Factor

40 Quantity of Sanitary Sewage: The quantity of sanitary sewage is mainly affected by the following factors: 1) Rate of water supply 2) Population 3) Type of area served as residential, commercial, industrial, etc. 4) Ground water infiltration. Determination: 1) Quantity of sanitary sewage should be equal to the quantity of water applied by water works but actually subtraction are done due to leakage or water being consumed in drinking, cooking, sprinkling, etc. 2) After doing all calculation, addition & subtraction, Quantity of sanitary sewage = 75 to 80 % of the total water supplied.

41 Variation in Quantity of Sanitary Sewage: 1) Practical average never flow in sewer, it continuously varies from hour to hour of the day and season to season. 2) The design of sewer should be done for the maximum possible flow. 3) Fluctuation is due to outcome certain local condition, habits, customs, holidays, season, etc. 4) Self cleansing velocity should be maintained in the case of minimum flow.

42 Variation in Sewage Flow Typical hourly variations in sewage flow

43 Maximum daily flow = Two times the annual average daily flow (representing seasonal variations) Maximum hourly flow = 1.5 times the maximum daily flow (accounting hourly variations) = Three times the annual average daily flow Minimum daily flow = 2/3 Annual average daily flow Minimum hourly flow = ½ Minimum daily flow = 1/3 Annual average daily flow

44 Design Period The future period for which the provision is made in designing the capacities of the various components of the sewerage scheme is known as the design period. The design period depends upon the following: 1) Ease and difficulty in expansion, 2) Amount and availability of investment, 3) Anticipated rate of population growth, including shifts in communities, industries and commercial investments, 4) Hydraulic constraints of the systems designed, and 5) Life of the material and equipment. 1. Laterals less than 15 cm diameter : Full development 2. Trunk or main sewers : 40 to 50 years 3. Treatment Units : 15 to 20 years 4. Pumping plant : 5 to 10 years

45 Important Factors Considered for Selecting Material for Sewer a. Resistance to corrosion b. Resistance to abrasion c. Strength and durability d. Weight of the material e. Imperviousness f. Economy and cost g. Hydraulically efficient Materials for Sewers Asbestos Cement Sewers Plain Cement Concrete or Reinforced Cement Concrete Vitrified Clay or Stoneware Sewers Brick Sewers Cast Iron Sewers Steel Pipes Ductile Iron Pipes Plastic sewers (PVC pipes)

46 Surface Drain Section: 1) Rectangular Surface Drain 2) Semicircular Surface Drain 3) U-Shaped Surface Drain 4) V-Shaped Surface Drain

47 Shapes of Sewer Pipes (a) Standard Egg Shaped Sewer ( b) New/ Modified Egg shaped Sewer Fig. Shapes of Sewer (c) Horse shoe sewer section (d) Parabolic section

48 (e) Semi-elliptical section ( f) Rectangular Sewer (i) Basket-Handle Section Fig. Shapes of Sewer (g) U-shaped section (h) Semi-circular Section

49 Egg Shaped Sewer:- 1) The depth of these sewer is 1.5m times of their width. 2) Constructed at site & made of concrete and brick arch with special invert at bottom or of RCC. 3) Better hydraulic property than circular with low discharge. 4) Used in both combined & separate system. 5) Most suitable for combined system bcoz gives self cleansing velocity even in DWF. 6) Equally suitable for separate system bcoz easily accommodate the flow of sewage with the development of the town. 7) Disadvantages are construction is difficult, less stable & requires good masonary backing.

50 Que. 2 Calculate the velocity of flow in a sewer of diameter 1.5m. The sewer is laid at a gradient of 1 in 550m. What will be the discharge through this sewer when running one-half full? Assume m = in Mannings formula. According to Manning s formula v = (1 / m) x r (2/3) x S (1/2) Hydraulic Mean Depth, r = (A/P) = d/4 for circular sewer running one half full r = 1.5 / 4 = 0.375m S = slope or gradient = 1 / 550 Putting values in Manning s formula, v = (1/0.012) (2/3) (1/550) (1/2) v = 1.84 m/s Q = A x v Q = ½ x (( x d 2 ) / 4 ) x (1.84) Q = 1.63 m 3 / s

51 Que. 3 Determine the velocity of flow in a circular sewer diameter 120 cm, laid on slope of 1 in 700, while flowing full. formula. r = 0.3m v = m/s Q = 1.47 m 3 /s Assume m = in Manning s

52 Que. 4 A sewer district has the Area = 5 hectors, Impermeability factors = 0.5, Design intensity of rainfall = 40 mm/hr, Density of population = 500 person per hectors, Average rate of water supply = 200 lpcd. Determine the sanitary sewage and storm water flow for design of sewer. Sanitary Sewage Flow: Average rate of water flow = 200 lpcd Assuming peak factor = 3 Area, A = 5 hector Population Density, Pd = 500 person per hector Q = 3 x A x Pd x flow rate Q = 3 x 5 x 500 x 200 Q = 1.5 x 10 6 Lit/Day Q = m 3 / s Strom Water Flow: Q = (A x C x R) / 360 Q = (5 x 0.5 x 40) / 360 = m 3 / s

53 Que. 5 Design the section of a combined circular sewer when area to be served = 150 hectares, population of locality = 50000, Max permissible velocity = 3.2 m/s, time of entry = 5 minutes, time of flow = 20 minutes, Rate of water supply = 270 liters/day/capita & Impermeability factor = Sanitary Sewage Flow: Assuming peak factor = 3.0 Maximum flow, Q = (3.0 x 270 x x 10-3 ) / (24 x 60 x 60) = m 3 / s Strom Water Flow: Time of Concentration = = 25 Minutes Intensity of Rainfall, R = ( a / (t + b)) when time conc. 20 to 100 minutes, a=760 & b= 20 R = (760 / ( )) = mm/hr Q = (A x C x R) / 360 Q = (150 x 0.45 x 16.89) / 360 = m 3 / s Combined Discharge = = m 3 / s Q = A x v A = Q / v A = / 3.2 = m 2 Diameter of sewer, D = ((A x 4) / ) = 1.2m

54 Que. 6 Design a storm sewer when area to be distributed = 5 hectors, effective impermeability factor = 0.4 & time of concentration = 20 minutes. Determine size and grade of the sewer if velocity is to be maintained 1 m/s. Rainfall intensity is given by R = (a) / ( b + t ) Take a = 750, b = 10 & m = Strom Water Flow: Time of Concentration = 20 Minutes Intensity of Rainfall, R = (a) / ( b + t ) R = (750 / ( )) = 25.0 mm/hr Q = (A x C x R) / 360 Q = (5 x 0.4 x 25) / 360 = m 3 / s Q = A x v A = Q / v A = / 1 = m 2 Diameter of sewer, D = ((A x 4) / ) = 0.42 m According to Manning s formula v = (1 / m) x r (2/3) x S (1/2) v = (1 / 0.015) x (D/4) (2/3) x S (1/2) 1 = (1 / 0.015) x (0.42/4) (2/3) x S (1/2) S = 8.6 x in 220m

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62 TYPICAL QUESTIONS 1) Define sewage, sewer & sewerage System? Explain in brief the data required in the planning of sewerage system? 2) Explain with neat sketches different shapes of sewer? 3) Draw a neat sketch of egg shape sewer & state advantages of disadvantage of it? 4) What do you understand by sewage collection system? Explain the various patterns of collection system? 5) How do you determine sewage production from city? Explain the various types of pipes used in Municipal Sewerage System? 6) What should be the characteristics of material to be used for sewers? 7) Describe the conservation system & water carriage system of sanitation with merits and demerits? 8) What do you understand by fluctuation in per capita sewage Production? State and explain the effects of these fluctuations in the design of sewage treatment plant? 9) Explain the rational method for estimating storm water? 10) What is Dry Weather Flow? Write briefly about the factors affecting DWF? 11) Design a suitable circular sewer to carry 1200 LPS of sewage. The sewer is running half full at a slope of 1 in 600. Assume manning s constant is ) If the total area is 5 hectares & the intensity of rainfall is 50 mm/hr, calculate coefficient of runoff. Assuming following data, Type of Area % of Total Area Runoff Coefficient Roofs & Pavements 40% 0.85 Lawns & Gardens 40% 0.20 Ground Surfaces 20% 0.10