Tag Archives: Rivers

The length of the Derwent River

Past readers of Frequently Asked Questions know that I have not been able to discover the ‘real’ length of the Derwent River.  In conversation recently with blog follower Yo, I was reminded of the challenges involved with determining river lengths.

If a river empties into a sea by more than one waterflow, then which is the ‘real’ river? Do we say there are two river lengths for the same river in such a circumstance?

If a river enters into a bay which opens onto a sea, where does the river end?

If the mouth of a river is a complex delta receiving silt flows and forever changing, can we pinpoint the location of the river mouth? At which time could a reliable measurement be made? No and never, are the answers to these questions.

At the source, rivers sometimes start with a dribble of water oozing from the ground. Is that enough to be able to define the water source as a river?  Some rivers pour from Lakes. Is the middle of the lake the start of the river or is that bank over which the water leaves the Lake, the official starting point? If a dam has been built at the junction of the lake and river, then the starting point may be the water at the top of the dam or at the bottom of the dam – leading to a different final river length.

What about rivers such as the Nile River which have at least two waterflows starting inland and which then meet to form one river?  Which waterflow counts towards the measurement of the river’s length? Or does the river start where the two or more waterflows merge?

Rivers do not travel in neat straight lines so should we measure the distance along the riverbank? If so, which bank?  The shape of the shoreline on either side of a river can be markedly different from each other and one side is usually longer than the other.

How about measuring the length of the river taking a centre line? Will that give the most accurate measurement?  This is the preferred method, however many of our measuring devices are straight – think ruler, think tape – so how can we make a reliable measurement?

On the first day in December 1873, the Commissioner of Patents for Inventions under England’s Patent Law Act 1852 recorded Edward Russell Morris’s invention of a pocket instrument which could measure distances on curved lines.  Since the 19th century, various variations have been developed.

If you check on EBay online, many historical versions of Opisometer Curvimeter Meilograph Map Measurers have been photographed, and are offered for sale. Opisometers have a tiny wheel at one end which, when rolled on a map along a road or river, connects with a graded scale in either a straight or circular format to read a distance. The unit markings refer either to kilometres or miles. You can watch a demonstration of one of these measuring tools on You Tube .

A bushwalking friend purchased an Opisometer many years ago and lent it to me so I could ascertain the length of the Derwent River more closely.  Today I used the Opisometer by rolling it on my maps, along an arbitrary ‘line’ in the centre of the river.


After using the Opisometer on all seventeen 1:25,000 maps that cover the Derwent River, it seems the length is 214 Kilometres (refer to Frequently Asked Questions for a table showing the breakdown per map).

Based on my measurements today, so far I have walked against 61 kilometres of that length.  I can see that any previous measurements reported in my blog, have been wildly inaccurate – generally too low.

Limited access roads, and limited direct access to the river from the land: Stage 14 of my walk along the Derwent River

A few times during my Stage 14 walk I noticed a sign ‘Limited Access Road’ and sometimes another sign indicating the Roads and Jetties Act 1935. This was true, for example, in the Sorell Creek area as I walked to New Norfolk. I wondered if this was Tasmanian state legislation affecting land ownership to the edge of the Derwent River.  Blog followers will have read my annoyance at not being able to walk along the exact river edge from time to time, because private property occupies the space and this is often gated and fenced. On my return home from the Stage 14 walk, I delved deeply into various pieces of legislation and other sites. This is what I discovered.

At http://www.ifs.tas.gov.au/publications/river-access-angler-rights-and-responsibilities, I learned that angler rights and responsibilities were as follows: “All anglers have an important role in maintaining good relations between landowners and the angling community. Firstly, anglers should understand that access is a privilege not a right, and secondly, when in doubt, ask permission. In Tasmania, most private land titles extend to the bank of the river and some titles extend to the middle of the river. This can mean that you may be trespassing, which is a criminal offence, even if you are wading in the river.

Rivers also flow through public land such as Crown Reserves, State Forests, National Parks, Hydro property and Conservation Areas. Whilst public access is usually permitted, different entry conditions may apply depending on the management authority.

The Inland Fisheries Service has been working to develop access to angling waters with a focus on improving foot access to major river fisheries. Much of this has involved negotiating with landowners and establishing formal agreements regarding access for anglers. Access points are now clearly marked with signs at the access locations on seven major river fisheries around the State.

Apart from registered private fisheries, Tasmania’s fishery is public property – the fish are not the property of the landowner. However, the land that surrounds public water is subject to title and the rights of the landowner to control access to the river or lake is at their discretion. Anglers must ensure that they are on public land or that they have sought the permission of the landowner to access the river or lake they wish to fish.

The majority of lakes in Tasmania exist on Hydro Tasmania or reserve land (Crown, National Parks etc) and public access is generally permitted across the land to the lakes and around the lake shores. Hydro does control access to areas where there is infrastructure or there are safety issues with public access. These areas are generally signposted with appropriate warnings.

Rivers generally traverse a number of different land tenures along their length, which may be a combination of reserves and private land. Land title generally extends to the edge of the river, and occasionally to the middle of the river. Land tenure can be searched on the LIST Tasmanian Property Database (www.thelist.tas.gov.au). Another useful tool is the Tasmanian 1:25000 map series, available from Service Tasmania. These show river reserves where they exist and anglers are permitted to access these areas provided they do not have to cross private property to reach them. The most important principle is ‘Access is a privilege not a right – when in doubt ask permission’.”

Stiles across fences have been installed for anglers and I saw a few of these during Stage 14 of my walk along the Derwent River.  These usefully provide access to sections but do not allow a continuous uninterrupted walk along the river’s edge.

 Stile jpeg

An 2007 article on the site http://www.exploroz.com/Forum/Topic/45914/Public_access_to_waterways_on_private_land.aspx

confirms this situation is similar across Australia, and it debunks some myths.

How does this get changed to allow easy public access to the river in Tasmania?  The permission must come from a State government minister under the Crowns Act 1976 (http://www.thelaw.tas.gov.au/tocview/index.w3p;cond=;doc_id=28%2B%2B1976%2BGS74%40EN%2B20131211000000;histon=;prompt=;rec=;term=). Clause 57 states: “Reservation of land abutting on streams. Where, in the opinion of the Minister, it is desirable to reserve Crown land –

(a) abutting on any permanent river, stream, or lake; or

(b) that is contiguous to the sea or an estuary –

he shall reserve, from any sale of that Crown land, land to the extent of at least 15 metres in width on each bank of the river, stream, lake, or the high-water mark of the sea or estuary.” I cannot imagine any government minister taking ‘rights’ away from current owners, so the chances of my lobbying successfully for a clear walking path next to the Derwent River are probably zero and zilch.

By the way, the interpretation clauses of the Roads and Jetties Act 1935 includes: a “country road means a road not being or forming portion of a State highway or subsidiary road, but does not include a street in any town”. I was reminded of an earlier post which tried to determine how a ‘back road’ might be defined.