How to compute irregular pond stage storage relationship according to MSMA?

Authority may request/inquire detailed breakdown on how MiTS software gets the ‘provided pond storage volume’. Calculation on the storage volume is based on the double-end area. 

“The storage volume for natural ponds in irregular terrain is usually developed for detention pond using a topographic map and the double-end area.”(MSMA 2nd Edition, 7.5.2)

The double-end area formula is expressed as:

Where, 

V(1,2) = Storage volume between elevation 1 and 2 (m3);

A1 = Surface area at elevation 1 (m2);

A2 = Surface area at elevation 2 (m2); and 

h = Change in elevation between points 1 and 2 (m).

Let’s check with textual report from MiTS;

Therefore, 

V at 1.5m storage = [(2540.16 + 2560.36) / 2] * (0.15-0.10) = 127.51 m3

Hence, this can be used as guidance on how the calculation is made in MiTS software.