Phetla.  I agree with another ...

Phetla.  I agree with another respondent, that constructing an equalization tank to capture the overflow will not solve your problem and is more expensive than simpler solutions.  It's clear your collection system suffers badly from inflow, and the sewer is subject to considerable debris content.  Bypassing the screen and discharging directly to the primary clarifier risks sending debris to the primary clarifier and consequential damage to downstream mechanical equipment and pumps.  Overflowing to an equalization basin will result high expense and trash accumulation in the basin, and given the problem occurs during high flow events it is questionable as to whether you can build a basin large enough to capture the resulting overflow.  That being said, it could function as a trash basin, rather than equalization basin.  This would require a smaller volume and could overflow to the primary clarifier. It would still require effort and cost to clean out after overflow events.  A better approach may be to add a second upstream screen with a bypass to the existing screen, effectively providing double the screen area and half the probability of an overflow event.  Addressing the community growth issue, you could later consider an overflow to a trash tank as a contingency measure, or replacing the manual screens with mechanically cleaned screens.