To most observers, the level (or presence) of water in the lake doesn't appear to be directly related to fluctuating annual rainfall or droughts: they are "out of sync".

Lake George was formed as a result of the headwaters of the Yass River (which once flowed through what is now Geary's Gap) being cut off by movement on a fault that is now reflected in the Lake George Escarpment.

Water and sediments from the "severed head" of the Yass River slowly accumulated in the basin that was formed on the eastern side of the fault. Eventually, sufficient sediment accumulated to absorb all of the water in drier periods and form a "buried" water table.

Now the lake only fills after extended periods of rainy weather, and because the lateral and vertical movement of groundwater is much slower than surface flows, there is a long lag time between wet-weather periods and the appearance of water in the lake. This lag is magnified by evaporation, which is a large factor in such a broad, shallow body of water.

Douglas Mackenzie, Deakin

David Crowe's report "Future generations of Australians will be left paying price if hefty cuts are made to immigration" (The Canberra Times, October 9, p4) is perhaps myopic rather than long-sighted?

It declares a necessity for population to continue increasing at its present rate of 1.6 per cent indefinitely to "address the ageing of the population". And net overseas migration currently contributes 62 per cent of that increase.

It must surely be about numbers rather than ageing. That's assuming the Productivity Commission was correct in 2015: "the long-run effects need not to be large because migrants themselves age. The degree to which the ageing of past migrants can be offset, and thus ageing of the population delayed, also depends on the rate of growth of net migration over time."

At the time, Peter McDonald also declared himself to be of similar opinion. We pay in advance for physical, intellectual, social infrastructure; or suffer the consequences as is increasingly apparent. It's an escalating problem for future generations. And indefinitely, as the push continues for increasing numbers.

Colin Samundsett, Farrer

It looks like the nearly completed ACT Court complex towering over Vernon Circle has created a precedent, with Barry Morris' proposed massive apartment and commercial development at City Hill (The Canberra Times, October 6).

City Hill is set to turn into a canyon, echoing noise, trapping exhaust fumes, providing no visual vistas or relief from the road below and creating conflict between pedestrian and road users.

Maybe extending Commonwealth Avenue with a tunnel under City Hill could rectify some of the ACT town planners' mistakes.

John Skurr, Deakin

Mike Quirk (Letters, October 7) questions the wisdom of developing the new Molonglo suburb of Whitlam on the northern side of the river before developing land closer to the proposed commercial centre. One reason might be that a water supply is readily available from the two water reservoirs on the ridgeline behind Weetangera. Apparently, these have the capacity to service Whitlam without creating supply problems for the south Belconnen suburbs they have served since the 1970s.

Also, the long-neglected Weetangera oval was rejuvenated a few years ago.

The landform in the Molonglo Valley has a shortage of level ground large enough to provide playing fields to service these new suburbs, according to a government source.

Robyn Coghlan, Hawker

With the announcement of the retirement of Nikki Haley as UN ambassador comes the unexpected suggestion of an insider replacement – US President Donald Trump's daughter, Ivanka. She is a fashion designer which may be useful as a lot of ambassadorial work does seem to involve "dress-ups".

While Mr Trump says no one "is more competent in the world" than Ivanka to be the replacement for Ms Haley, she may find that the complexities of some situations challenging.

The situation in Ireland can be seen as a green versus orange problem so maybe the fashion world might have something to offer. The Korean region is more than just two teams, the North and South sides not playing nice. Let's not even contemplate how the most competent ambassadorial candidate would work with the Middle East countries.

Ivanka does have a skill that may help – she speaks French and she is wise enough to squash the suggestion immediately.

There must be a great number of ambassadors spinning in their graves or swivelling in their leather seats at the suggestion that they are less competent than a fashion designer.

The issue of potential nepotism is best avoided at the moment given recent discussions of President Trump's family support for him and tax concerns.

Don't ever doubt it's a weird, weird world and could still get weirder.

Dennis Fitzgerald, Box Hill, Vic

In last week's Sunday Canberra Times we were told about a letter by Einstein, which belittled religion, going up for auction.

Just as we'd never accept our mechanic's medical advice, no matter how good a mechanic he was, neither should we be impressed by what Einstein thought he knew about God and religion.

Want to know about God and religion?

Go to a good theologian, and try living the religious life as well. Here you might get some insight, providing its genuine complexities don't get in your way.

Vasily Martin, Queanbeyan

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