Environmental Engineering-I

Transcription

1 Environmental Engineering-I Prof. Dr. Muhammad Zulfiqar Ali Khan Engr. Muhammad Aboubakar Farooq Department of Civil Engineering The University of Lahore 1

2 Future Water Requirements Depend upon: 1. Selection of PER CAPITA Water Consumption 2. Future Population Forecast 3. Design Period 2

3 Design Period It is the number of years in FUTURE for which the proposed facility would meet the demand of the community. OR This is the period into the FUTURE for which estimation is to be made. 3

4 Factors affecting Design Period Selection of an appropriate design period for a particular facility / component of water supply system is very important and dependent upon following factors: 1. Length or Life of Structures. 2. Ease of Extension. 3. First Cost 4. Economy of Scale 5. Lead Time 4

5 Factors affecting Design Period 1. Length or Life of Structure: - Pumps - Conduits (Type of Pipes) Type of Pipe Steel Pipes Cast Iron Pipes Concrete Pipes Average Service Life Years 100 Years 75 Years 5

6 Factors affecting Design Period 2. Ease of Extension: This factor affects design period of whole Water Supply System depending upon the easiness with which its components can be enlarged i.e. effort with which Capacity of the components can be increased. e.g. - Tubewell : Easy to drill. - Treatment Plant : Easy to enlarge. 6

7 Factors affecting Design Period 3. First Cost: In case of High first cost and High Rate of interest, design period should be SHORT, so that the total cost of the project should not be distributed to present population only. e.g. Houses 7

8 Factors affecting Design Period 4. Economy of Scale: Economy of Scale means that per unit production cast of a facility decreases with the increase in scale (size) of facility. 8

9 Factors affecting Design Period 4. Economy of Scale: (Contd ) Example: 200mm diameter W/S pipe, 1km Long serves 3000 Persons. Cost = Rs. 300,000 => Cost/Head = Rs mm diameter W/S pipe, 1km Long serves Persons. Cost = Rs. 480,000 => Cost/Head = Rs. 40 9

10 Factors affecting Design Period 5. Lead Time: It is the time from the perception of the project to its start of operation. Lead Time = Time for Design of Project + Construction Time When lead time is MORE, MORE will be the design period. 10

11 Design Periods and Design Flows for Various Water Supply System Components 1. Large Dams, Transmission Main (Conduit) These are COSTLY and difficult to enlarge. Design Period: 25 to 50 Years Reservoir: Design Capacities of Reservoirs should be adequate to provide MAXIMUM DAILY DEMAND Conduit: Generally designed for MAXIMUM DAILY DEMAND at the end of Design Period. 11

12 Design Periods and Design Flows for Various Water Supply System Components 2. TUBE WELLS: These are easy to drill. Design Period: 5 Years Designed at PEAK HOURLY DEMAND, if NO Storage is to be provided. Designed at MAX. DAILY DEMAND, if storage is to be provided. 12

13 Design Periods and Design Flows for Various Water Supply System Components 3. Water Treatment Plant: Easy to enlarge. Design Period: Years. Designed for MAXIMUM Daily Flow. 4. Pumping Station: Easy to enlarge. Design Period: 10 Years. 13

14 Design Periods and Design Flows for Various Water Supply System Components 5. Distribution System: Difficult to REPLACE. Design Period: 25 Years. Designed for: MAX. DAY DEMAND + FIRE DEMAND. PEAK HOURLY DEMAND. Whichever is greater. 14

15 ADEQUATE Design Period in Water Supply System is provided because: Too Frequent extensions of the system are not possible. Reasonable economies of scale are achieved. 15

16 Components of Water Supply System 1. Collection : Dams, Reservoir, Intake, Pumping Station, Tube wells. 2. Transmission : Conduit, Valves, Pumping Station, Gravity Flow. 3. Treatment : Sedimentation, Coagulation, Filtration, Storage Disinfection, 4. Distribution : Pumping Station, Overhead Reservoir, Mains, Pipes, Valves, Fire Hydrants 16

17 Problem No. 1 A community is expected to reach a population of in 20 years. The present population is and present average Water consumption is m 3 /day. The existing Water treatment plant has design capacity of m 3 /day. Assuming an arithmetic growth rate of population growth, Determine in what year the existing plant will reach its design capacity. Assume plant has been designed on Maximum daily Consumption Basis. 17

18 Problem No. 2 The present population of a community is increasing at a geometric growth rate of per year. The present water requirement is fully met by a number of tube wells installed in the city. The average Water consumption is 350 lpcd. Using a design period of 15 years, Calculate the additional tube wells of 3.4 m 3 /min capacity of each tube well to meet the demand of design period. 18

19 Problem No. 3 A small community had a population of and in the census year of 1991 and 2001 respectively. Assuming a geometric growth rate and an average water consumption of 300lpcd, Calculate the design flow for the treatment plant and the transmission mains. Select an appropriate value of design period. 19