Problem: gravity draining tank through sloped pipe, falling head

With a lot of perseverance you could probably do it the way you have proposed. An easier way would be to write a spreadsheet where the flow rate is calculated as a function of height. Then copy the formulas into 100 (or 1000) rows - one row for each horizontal slice from the top of the tank to the base. With the calculated flow rate for each slice calculate the time required to drain that slice. The flow rate for each slice would be based on the height to the mid-point of the slice and the flow rate is taken as a constant for that slice. Add up the times for the 100 slices and you have your answer.

Katmar Software
Engineering & Risk Analysis Software

this is a common problem for stormwater engineers, there is free public domain software out there that can do this. (however, you can integrate it also if you would rather do it that way) HEC-1 is one example. SWMMM is another. In addition to the givens you have listed, downstream channel and tailwater conditions will affect the discharge rating curve. Also, your discharge rating curve may vary from orifice to weir flow depending on the depth in the detention basin.

you will need the
discharge rating curve
storage rating curve and
inflow hydrograph (if any)

thateb,

You've got valid input from posts above.
The link below reports some practical examples worked out, which could help you.

thateb

To answer your last question, the way to change your profile designation (from chemical to civil) is to click the "red flag" and ask the administrators to change it.

Patricia Lougheed

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Made me go through my fluid dynamic books, here's your answer (from "2500 solved problems in fluid mechanics and hydraulics"
By Jack B. Evett, Cheng Liu):



Hope this would help.