Just a thought from an out and out amateur.....when departing from 34 why can't aircraft fly up the Hutt Valley rather than over Newlands ridge if it causes so many problems? At least that way the distance is much longer to achieve the height necessary.
At Hayward's Rd a left turn would necessitate approx. another 120 metres to climb in excess of the Newlands ridge but gives another 14kms to achieve it.
The extra distance to overfly Paraparaumu for instance is about 3km.
To a layman this seems all too simple....why doesn't it happen?