<p>Irrigation and farm dams on or near rivers only make the water available in the vicinity of the dams. They prevent the trapped/dammed water from flowing downstream, as it naturally did, and being available to the ecosystem downstream of the dam.</p>
<p>The perfect example of this is the dams on the cotton farms in southwest Queensland which starve the Darling River of water, resulting in algal blooms and massive fish kills downstream in New South Wales.</p>
<p><em><a href="https://theconversation.com/excessive-water-extractions-not-climate-change-are-most-to-blame-for-the-darling-river-drying-192621" rel="nofollow noreferrer">Excessive water extractions, not climate change, are most to blame for the Darling River drying</a></em></p>
<p><em><a href="https://theconversation.com/while-towns-run-dry-cotton-extracts-5-sydney-harbours-worth-of-murray-darling-water-a-year-its-time-to-reset-the-balance-133342" rel="nofollow noreferrer">While towns run dry, cotton extracts 5 Sydney Harbours’ worth of Murray Darling water a year. It’s time to reset the balance</a></em></p>
<p><em><a href="https://www.theguardian.com/australia-news/2019/jan/31/photos-reveal-queensland-cotton-farms-full-of-water-while-darling-river-runs-dry?utm_term=RWRpdG9yaWFsX0d1YXJkaWFuVG9kYXlBVVMtMTkwMTMx&amp;utm_source=esp&amp;utm_medium=Email&amp;utm_campaign=GuardianTodayAUS&amp;CMP=GTAU_email" rel="nofollow noreferrer">Photos reveal Queensland cotton farms full of water while Darling River runs dry</a></em></p>
<p><em><a href="https://www.abc.net.au/news/2023-03-18/nsw-menindee-mass-fish-kill-worst-in-region/102115184" rel="nofollow noreferrer">Millions of fish dead in the worst mass kill ever to hit Menindee region, in NSW's far west</a></em></p>
<p><em><a href="https://www.abc.net.au/news/science/2024-04-30/murray-darling-basin-menindee-fish-kills-causes-solutions/103745622" rel="nofollow noreferrer">Why are fish still dying in the Darling River at Menindee — and what can we do to prevent it?</a></em></p>
<p><a href="https://www.csiro.au/en/news/All/News/2023/March/Expert-Commentary-on-Menindee-fish-kill" rel="nofollow noreferrer">Expert commentary: Menindee fish kill</a></p>

CC BY-SA 4.0
2024-11-08T23:24:03.890Z
2024-11-08T23:24:03.890Z
Fred
<p>The volume that flows through the system as liquid water decreases because of evaporation in reservoirs.  For example, the Lower Colorado River system <a href="https://www.usbr.gov/lc/region/g4000/4200Rpts/LCRBEvapReport/evapreport.html" rel="nofollow noreferrer">loses ~750k acre-feet per year</a>, or just short of a billion cubic meters, to major reservoir evaporation, which is roughly 10% of its allocation.</p>
<p>The argument made for increases is that water can be released when it's most beneficial, instead of &quot;excess&quot; water just running off to the sea, and minimum flows can be guaranteed.  That's technically possible; the minimum flow thing isn't unheard of, and it's certainly better to have something than to just dry up the river during summer irrigation, but I'm not aware of any major cases where a reservoir is actually regarded as benefiting the ecosystems downstream.  More typically, there still isn't enough water in parts of the year, and reservoirs also block off sediment movement and are usually used to prevent ecologically-important high flows.</p>

CC BY-SA 4.0
2024-11-08T16:01:39.900Z
2024-11-08T16:01:39.900Z
damp_civil
<p>This is probably a silly question but here we go.</p>
<p>In Australia we have a lot of dams particularly in the north drawing from our biggest river system - the Murray Darling.</p>
<p>Now since I can remember water management has been a contentious issue. Farmers steal more than their allotted share and consequently our river system has been in a state of decay verging on death for quite some time.</p>
<p>My question is this. Farmers will argue that their dams actually add to the sum total of water available in the ecosystem. But is this actually true? If we look holistically do the dams near this river actually increase the total water capacity of the area? Or is it more correct to say the total volume of water in the area is constant however it's distribution is more concentrated?</p>
<p>If this is increasing total water capacity. Where is the extra water coming from?</p>

<hydrology><ecology>
Total systemic water volume
nathan carr
# Total systemic water volume

(Asked by: username_0 on 2024-11-07)

This is probably a silly question but here we go.

In Australia we have a lot of dams particularly in the north drawing from our biggest river system - the Murray Darling.

Now since I can remember water management has been a contentious issue. Farmers steal more than their allotted share and consequently our river system has been in a state of decay verging on death for quite some time.

My question is this. Farmers will argue that their dams actually add to the sum total of water available in the ecosystem. But is this actually true? If we look holistically do the dams near this river actually increase the total water capacity of the area? Or is it more correct to say the total volume of water in the area is constant however it's distribution is more concentrated?

If this is increasing total water capacity. Where is the extra water coming from?

**Tags:** hydrology, ecology


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## 2 answers

### Answer by username_1 on 2024-11-08. Score: 2

Irrigation and farm dams on or near rivers only make the water available in the vicinity of the dams. They prevent the trapped/dammed water from flowing downstream, as it naturally did, and being available to the ecosystem downstream of the dam.

The perfect example of this is the dams on the cotton farms in southwest Queensland which starve the Darling River of water, resulting in algal blooms and massive fish kills downstream in New South Wales.

*[Excessive water extractions, not climate change, are most to blame for the Darling River drying](https://theconversation.com/excessive-water-extractions-not-climate-change-are-most-to-blame-for-the-darling-river-drying-192621)*

*[While towns run dry, cotton extracts 5 Sydney Harbours’ worth of Murray Darling water a year. It’s time to reset the balance](https://theconversation.com/while-towns-run-dry-cotton-extracts-5-sydney-harbours-worth-of-murray-darling-water-a-year-its-time-to-reset-the-balance-133342)*

*[Photos reveal Queensland cotton farms full of water while Darling River runs dry](https://www.theguardian.com/australia-news/2019/jan/31/photos-reveal-queensland-cotton-farms-full-of-water-while-darling-river-runs-dry?utm_term=RWRpdG9yaWFsX0d1YXJkaWFuVG9kYXlBVVMtMTkwMTMx&utm_source=esp&utm_medium=Email&utm_campaign=GuardianTodayAUS&CMP=GTAU_email)*

*[Millions of fish dead in the worst mass kill ever to hit Menindee region, in NSW's far west](https://www.abc.net.au/news/2023-03-18/nsw-menindee-mass-fish-kill-worst-in-region/102115184)*

*[Why are fish still dying in the Darling River at Menindee — and what can we do to prevent it?](https://www.abc.net.au/news/science/2024-04-30/murray-darling-basin-menindee-fish-kills-causes-solutions/103745622)*

[Expert commentary: Menindee fish kill](https://www.csiro.au/en/news/All/News/2023/March/Expert-Commentary-on-Menindee-fish-kill)


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### Answer by username_2 on 2024-11-08. Score: 1

The volume that flows through the system as liquid water decreases because of evaporation in reservoirs. For example, the Lower Colorado River system [loses ~750k acre-feet per year](https://www.usbr.gov/lc/region/g4000/4200Rpts/LCRBEvapReport/evapreport.html), or just short of a billion cubic meters, to major reservoir evaporation, which is roughly 10% of its allocation.

The argument made for increases is that water can be released when it's most beneficial, instead of "excess" water just running off to the sea, and minimum flows can be guaranteed. That's technically possible; the minimum flow thing isn't unheard of, and it's certainly better to have something than to just dry up the river during summer irrigation, but I'm not aware of any major cases where a reservoir is actually regarded as benefiting the ecosystems downstream. More typically, there still isn't enough water in parts of the year, and reservoirs also block off sediment movement and are usually used to prevent ecologically-important high flows.


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