wastewater pumpstation operational storage modelling 1

[swazimatt]

I would like to know what the standard modelling procedure is for PWWF, PDF and ADF for wastewater. My understanding is that PWWF is for an hour in the morning and evening, but how would i model the rest of the day?

We have a pumpstation proposed where the receiving network can only accept about 50% of the peak wet weather flow so the pump will discharge at 50%PWWF and the balance will be stored and pumped as the flow into the pumpstation reduces down to average flow.

Is there a standard document i can refer to where it says under wet weather flows, peak is expected to be for 1hr, the flow will then reduce over x hours until it achieves ADF (or average wet weather flow?) this way i can determine the size of the additional storage tank and also demonstrate that it will clear before the next peak 12 hours(?) later

 

[Kodiak31]

"My understanding is that PWWF is for an hour in the morning and evening," I think you are referring to Peak Hourly Flow. Functionally, your definition is probably close enough.

Peak wet weather flow (PWWF) is a function of the leakiness of the collection system and the characteristics of the design storm you are attempting to model. There is no true "peak" as there is always a larger storm which could occur (10-year, 25-year, 100-year, etc.) which would likely produce a higher wet weather peak flow and volume in the collection system. There are also less intense but lengthy wet weather periods which can produce a large volume of wet weather flow which can fill your storage even if flows never approach the "peak".

Typically, you would estimate the PWWF flow rate and the resulting design storm sanitary hydrograph by flow metering during a few storm events and then projecting flows up to whatever design storm you decide upon or your regulator requires. This is often done with a temporary flow meter and rain gauge installation to study some smaller storms (or a big one if you get lucky during the flow metering period), then unit hydrograph methods to define the wet weather component and project to your design. If you are sizing storage, you will need a hydrogaph. In deciding upon a design storm you should consider consequences of failure (i.e., your storage being exhausted). Is this likely to flood basements? Relieve to grade? Overflow to a waterway?

There is no standard guidance as every collection system is unique(more or less susceptible to inflow and infiltration, different soil conditions, combined sewers, separated sewers, etc.).

 

[swazimatt]

makes sense, thanks