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A guide to Goulburn Rivers water levels and management
I much appreciate your regular fishing reports and the effort you put into it. However, for virtual fly fishing beginners such as myself, I believe that if you were to publish a background paper on Goulburn River water flows that beginners would get more from the reports. For example, the Goulburn River level @ 130 megalitres a day. What does this mean? (I assume that is the volume released via Eildon per day). Is there a statutory requirement to release a minimum flow? If there is what is it? What impact does the raising or lowering of water levels in the Goulburn have on hatches, likelihood of fish to take flies, differences in approach that fly fishers should take, and the like? I don’t believe that such background info need be provided on an ongoing basis but perhaps as a one-off intro to your reports for the new season. Please keep up the good work. I look forward to the resumption of your reports.
Regards and thanks
Thanks for the email Bruce. I will attempt to answer your questions and shed some light on the management of the state’s most popular trout river. I hope this helps you to better understand how this river works.
Goulburn River Management Overview
The Goulburn River plays a crucial role in transporting irrigation water from Lake Eildon downstream to the Goulburn Valley, a region known for its thriving agricultural industry. While the river also serves as a source of drinking water for towns and supports recreational activities along its entire length, its primary function is to deliver water for agricultural purposes during the dry months between October and April each year.
Essentially, rainfall is captured in Lake Eildon during the wetter months and then distributed downstream when it is most needed during the long, dry summers. This creates an atypical situation where the river experiences low and warmer flows in winter and spring, and high and cooler flows in summer. This flow regime contrasts with nearby streams that run high and cold in winter and low and warm in summer, making the Goulburn River an exceptional habitat for trout.
Goulburn Murray Water (GMW) is responsible for overseeing the management of water releases from Lake Eildon to the Goulburn River.
Lake Eildon boasts over 500 kilometers of shoreline and, when full, holds seven times the volume of water of Sydney Harbor. The dam wall, situated at the township of Eildon, acts as a natural choke point in the valley, blocking the flows of several rivers, including the Jamieson, Big, Howqua, Delatite, and Upper Goulburn.
Water Releases – Lake to Pondage
Water is primarily taken from Lake Eildon via the main power station rather than the spillway itself. Although the spillway is occasionally used during times of higher water levels or to test its function and operation, water is almost always released from the out-take tower into the Pondage via the power station, generating electricity from the drop in height between the lake and the pondage.
The water released from the power station does not flow directly into the river from the lake. Instead, it is held in two interconnected pondages (smaller lakes) located immediately beneath Lake Eildon and adjacent to the town. Collectively known as “the Pondage,” these lakes hold approximately 5,200 megaliters.
The water cannot flow directly from the lake to the river because the out-take tower in the lake does not allow for the precise regulation of the lower flows often required for the river. This is important because the water is being sold and there is money at stake. As a result, water is first delivered from the lake to the Pondage and then more accurately regulated when released from the pondage gates to the river.
The Pondage’s water level frequently changes depending on irrigation and occasionally electricity demands. While these fluctuations may seem unpredictable to casual observers, there is most definietly a method to what is often thought of as madness. For instance, when the river is at high summer levels (i.e., 5,000+ MLD), the Pondage will fill and drain daily due to its limited storage capacity of only 5,200 megalitres. Conversely, when the river flows at winter/spring levels (i.e., 400 MLD), the Pondage level remains relatively stable for day, even weeks at a time, no observable changes.
Water is released from the Pondage into the Goulburn River via the pondage gates and occasionally through a small power station at the lower end of the Pondage. This secondary release point allows for precise regulation of water levels, even down to the lowest flow rates.
Statutory Requirements – Minimum Water Levels Goulburn River
Flow-regulated rivers like the Goulburn River are subject to various requirements that water managers must adhere to. The most relevant aspect for anglers is the minimum riparian flow or environmental flow. Recently, this mandatory minimum was raised from 130 ML/D to 400 ML/D, benefiting both trout and fly fishers. This increase will have positive long-term effects on the fishery.
This new height must be maintained to meet domestic and stock water requirements downstream. Initially, it was believed that the environmental flow aimed to maintain a healthy state for all organisms, including fish and macroinvertebrates. However, it was later clarified that its primary purpose is to deliver basic water supplies to towns and farms downstream.
The 400 MLD level is set for most of May through late September/October. While this level restricts trout spawning success in the river, with 1,500-3,000 MLD being closer to ideal conditions, it is still an improvement compared to previous low levels mandated as minimums.
Units of Measure
Megalitres per day (MLD) is a common term used to discuss water flow rates. A megalitre is equivalent to a million litres or, for a visual representation, the amount of water contained in an Olympic-sized swimming pool. Therefore, 400 MLD means that 400 million litres of water are released daily, passing by any point on the river within a 24-hour period. While this may seem like a lot, it is the minimum flow required by law.
– Summer releases typically range from 4,000 to 6,000 MLD.
– When Lake Eildon is full, releases can reach 8,000 to 12,000 MLD.
– The largest releases observed were around 40,000 MLD.
*Note: A megalitre is equivalent to 220,000 gallons or 1,000 kilolitres.
The irrigation season runs from August 15 to May 15 each year. During this time, farmers can purchase water for irrigation purposes based on their license and the annual allocation determined by regulators (GMW). The flow rate varies depending on factors such as weather forecasts and rainfall predictions, which influence farmers’ water usage.
In addition to irrigation, power generation plays a significant role in determining water releases from Lake Eildon. Power companies have their own water entitlements and may require more water than what is requested by farmers. The relationship between power generation, irrigation supply, and water releases is complex and interconnected.
While water levels impact the fishing quality for those unfamiliar with the river, factors such as water temperature and dissolved oxygen levels are more significant indicators of likely fishing conditions.
However, understanding the effects of water levels on fishing is still important:
1. Low levels (May-October): Flows of 1,000 MLD or less (usually 400-500 MLD) allow for easy wading access and less water between fish. Preferred by most anglers, but fish can be shy.
2. Low-Mid Levels (October-November and April): Flows between 1,000 and 2,500 MLD. Traditional river structures are visible, providing ideal trout habitat. Excellent for fly fishing and insect hatches.
3. Mid Levels (November and late March/April): Flows from 2,500 to 6,000 MLD. Stream structures gradually disappear, but the fishing is excellent, especially for drift boating.
4. High Levels (December – mid-March): Flows above 6,000 MLD. Typical trout stream structures vanish, making the river appear unfishable to those unfamiliar with it. Flooded bays, lagoons, and billabongs become important fishing areas.
For anglers seeking success on the Goulburn River, it’s crucial to understand water flow rates, irrigation season dynamics, power generation demands, and the effects of water levels on fishing conditions. With this knowledge, you can better plan your fishing trips and adapt your strategies to the changing river conditions.
Rapidly Changing Levels
One of the most contentious issues in tailwater fisheries worldwide is the rapid change in river height, either up or down. In regions where trout are highly valued, strict regulations dictate how dramatically water levels can be altered within a given period. Unfortunately, such measures are lacking in many areas. Nonetheless, it’s essential to understand the implications of these changes.
A sudden, dramatic shift in river height can negatively impact the fishing, but for the most part it doesnt. Fish are creatures of habit and become familiar with their surroundings, finding shelter, feeding lies, and prime lies within their territory. When the river height changes drastically, fish must relocate and start this process anew.
Trout are highly adapatable and will continue to find food and eat, the disruption sometimes forcing them to find new lies, but they are ever on the hunt for food, and changes in river height often results in a change of feeding patterns rather than a cessation of feeding activity.
Which is more challenging – a quick rise or a quick drop?
Well, it depends.
A quick rise doesn’t force fish to retreat further or deeper into the riverbed. Although their underwater environment changes, they aren’t forced to relocate, and often the extra volume of water will dislodge aquatic insects and rise over new ground drowning terrestrials like beetles, ants, and grasshopper. Fish must move to find the best lies at the new river height, but it’s not a severe issue.
On the other hand, dropping levels can have a more significant negative impact on fish, forcing them to relocate as areas they may have been feeding in are quickly exposed. Sudden, sharp drops in height can cause challenging fishing conditions, not because the food supply is impacted. Quite often, sudden drops in river height/flow trigger large hatches of mayfly and caddis. Instead, these changes can result in disruption to the fishing as they can cause a mass relocation of the fish population, forcing new competition for prime lies.
Exceptions to these general rules do exist. For example, a large drop in water level can result in excellent fishing during autumn. After months of high flows, aquatic insect hatches diminish as the bugs sense a flood event and wait it out. When water levels fall away drastically, as an example from 8,000 ML/D to 2,000 ML/D, sub-aquatic creatures must move or die, resulting in many being swept away by the current and becoming accessible to the fish. This sudden increase in the number of insects drifting in the water column, can produce some of the best fishing of the season.
Conversely, a sudden dramatic rise can worsen fishing conditions. As water levels increase, it can set every twig, leave and branch along the waters edge set adrift as well as cause discolouration until the new water pushes through. Fortuntaely this only takes a few hours to clear. Dramatic increases in water levels can reduce hatches further due to drops in water temperature, reduced light intensity on the riverbed, and changes in water pressure.
Understanding water flow rates, irrigation season dynamics, power generation demands, and the effects of water levels on fishing conditions is essential for anglers looking to maximise their success on the Goulburn River. With this knowledge, you can better plan your fishing trips and adapt your strategies to the changing river conditions.
BREAKING THE RULES
So when is the best time to come up for a fish? Well like my ex-business partner Geoff still says, it’s whenever you get the time! I used to hear him say that over and over to people on the phone and I would just cringe and dismiss it out of hand. But as I am spending more time fishing in different places for different species, I am coming to realise that he is dead right. Some of the best bass fishing I have had has been on a crashing barometer despite the rules. The best bream fishing I had a few weeks ago was on the bottom half of a falling tide. The rules are just guidelines; not laws that are set in stone.
The more time I spend on the water, the more I realise that it’s about reading and interpreting what is going on, rather than trying to pick the perfect time to go fishing. If we only went out when the conditions were ‘perfect’, we wouldn’t have a business and we would have caught a fraction of the fish that we have.
Thanks for Reading
I hope that this has helped you to make some sense of the river and how it is managed in terms of water releases, and how we approach the differing river heights. If you wish to read an overview of a fishing season on the Goulburn, please click here.
River Level Photos
Please use the photo below to get an idea of the differing river heights. Photos were taken off Gilmore’s Bridge located between Alexandra and Thornton, looking downstream from the bridge. Clicking on the image will give you a larger version that is formatted width wise to fit on an A4 but it will use three sheets as there a number of pics to compare.