A Dry Spill Traditional Geocache

As with all of our 4x4 caches we have no way of knowing you or your vehicles capabilities and our idea of medium may differ to yours so please be sure you feel confident with the tracks before attempting this cache.

This is the third and last in this series showcasing some of what the Thompson Catchment has to offer. We recommend coming from GCZG36 - Santa’s Rum Place and then onto GC1KFXE – Another Thompson Viewand then to this one. After you have completed this you can just keep going down hill, cross the Thompson River and then back onto the main road near the top of the Dam wall making a nice circuit drive.

We were going to place a cache here a few years back but the track was quite difficult and there was no safe parking near GZ. The track has been improved but will still need a high clearance vehicle with low range and this is reflected in the terrain rating. This track is not subject to seasonal closures but DO NOT attempt it if it has been wet!

At GZ you will be able to park up to 4 vehicles off the track and be rewarded with some great views of the massive Thompson Reservoir wall that towers 165 metres above the river. The main dam wall is 590 metres long. You can also see the size of the spillway that has unfortunately not seen use since the last time the reservoir overflowed in October, 1996.

The Thomson scheme was built in several stages. In the early 1970s many kilometres of tunnels were drilled and blasted through the rock of the Great Dividing Range to allow water from the Thomson River to flow into the Upper Yarra Reservoir. Preliminary work on the Thomson Reservoir dam wall started in 1976 and the massive wall was completed and ready to store water and supposedly draught proof Melbourne by 1983.

The Thomson Reservoir has a capacity of 1,068,000 megalitres and is the largest in Melbourne's water storage system. When we placed the cache on 4/1/09 it held only 214,118 megalitres in other words 20.1%.

Around 18% of the Thomson River Basin water flows into the Thomson Reservoir. In recent years approximately 46% of reservoir outflow has been used to supply Melbourne and around 54% has been released for maintaining environmental flows and supplying irrigation areas downstream. Water from the Thomson Reservoir is pumped to the Upper Yarra Reservoir and to Silvan Reservoir for distribution throughout the metropolitan area.

After you leave GZ and get to the bottom of the track where it crosses the Thompson River please check the depth prior to crossing. We have not seen it above the sill on our Landcruiser on any visit but it pays to err on the side of caution.