What is sewage flow variation?
Sewage flow varies in sewerage which is dependent upon the time of any day. The variation of flow when plotted on a graph with time is called sewage variation flow graph.
Fluctuations in sewage flow
Fluctuations occur in sewage volume and average daily flow. Flow fluctuation occurs hourly and seasonally. Typical hourly fluctuations in wastewater mostly occur. If the flow rate is measured in the morning time, it will be the peak flow.
If the wastewater needs to travel long distances, the peak of the fluctuation graph will shift. That is the time it takes to collect enough sewage to fill the sewer, and the time spent on the trip. As the sewage flows into the sewer, more and more sewers get mixed in. This is because the area where sewerage is maintained is continuously increasing. This leads to reductions in sewage flow fluctuations and delay times continue to increase.
Size of displacement fluctuations vary from place to place and are very difficult to predict. For smaller communities, this variability is even more pronounced due to the shorter length and distance travelled.
What are the variousFlow rates?
The time it takes for the sewage to reach the main sewer is called flow rate.
For large cities, this variation is less. The following relationships can be taken into account when estimating the design flow rate:
Maximum daily flow rate = Twice the annual average daily flow rate (Seasonal fluctuation)
Maximum flow per hour = 1.5 times the maximum flow per day (billed hourly)
Fluctuation = 3 times the annual average daily flow rate
As the inflow area increases, the peak flow per hour decreases.
For small groups (Less than 50,000), peak factor can be 2.5. If the serviced population increases, the value decrease. For big cities, you can expect about 1.5 to 2.0. Therefore, the peak discharge in the receiving area can be regarded as 1.5 times the annual average daily discharge.
Also, in the design of wastewater treatment facilities,
The peak factor is estimated to be 1.5 times the average daily flow rate per year.
The minimum flow through the sewer is also important for increasing self-cleaning speed to avoid silt in the sewer. This flow occurs in the sewer at midnight. The impact of this flow is more pronounced on the side channels than on the main channel.
Check the minimum speed as follows:
Minimum daily flow rate = 2/3 year average daily flow rate
Minimum time flow rate = ½ Minimum daily flow rate = 1/3 yearly average daily flow rate
The overall variation between the maximum and minimum flow rates is greater and less on the sides.
In the main sewer system, this ratio can exceed 6 laterals and 2-3 for cases from the main channel.
Conclusion
Here a lot of flow variations can be seen which varies daily, hourly or seasonal.
The sewerage system is affected by the flow variations. If flow variations are not included in the sewage design, the pipes may be scoured and leakage may happen. So to ensure proper and fully functional sewage system, we must understand the role of flow variations.
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