Q1: rd or th extra space is left in sewer pipes at maximum discharge for

ANS:D - all the above.

The extra space left in sewer pipes at maximum discharge for accommodating potential increases in flow is typically referred to as "allowance for future growth" or "design margin." This additional capacity serves several purposes:

1. Low estimates of the average and maximum flows: Sewer systems are designed based on anticipated flow rates, but these estimates may not always accurately reflect actual conditions. By including extra space in the pipes, the system can handle higher flows than initially projected, ensuring that it does not become overwhelmed during peak usage periods or unexpected events.
2. Large scale infiltration of stormwater: Infiltration of stormwater into sewer systems can occur due to various factors such as cracks in pipes, faulty connections, or groundwater intrusion. During heavy rainfall or periods of high groundwater levels, infiltration rates can increase significantly, adding to the flow in the sewer system. The extra space in the pipes helps accommodate this additional flow without causing backups or overflows.
3. Unexpected increase in population: Population growth can lead to increased wastewater generation, putting additional stress on sewer systems. By leaving extra space in the pipes, the system can accommodate higher flows resulting from population growth without the need for immediate expansion or upgrades.

Therefore, all of the options provided are correct:

• Extra space in sewer pipes at maximum discharge accounts for low estimates of the average and maximum flows.
• It also accommodates large-scale infiltration of stormwater into the sewer system.
• Additionally, it provides flexibility to handle unexpected increases in population and associated wastewater flows.

Including a design margin or allowance for future growth in sewer system planning helps ensure that the infrastructure can effectively meet the needs of the community both now and in the future, while also reducing the risk of system failures or capacity issues.