A summer spate …….. maybe?

In time honoured fashion just as my delphiniums come into bloom ……… the weather breaks resulting in them being flattened by the incessant rain and wind. There has been a wee bit of discussion here and on Facebook what condition the river will be in over the next couple of days so I though it might be interesting to illustrate the impact of water abstraction on our water.

According to the SEPA rain gauges, in the last 36hours up to 9pm  37.2 mm of rain was recorded in Drum (Crook of Devon), 26.6mm in Tillicoultry, 48.4mm at Balado and 42.6mm at Kinkell Bridge (on the other side of the Ochils). On most rivers this would result in a big clearing spate but not necessarily so on the Devon.

It is worth looking at the SEPA river level gauges on the Devon and compare with some of our neighbours using some screen grabs from earlier in the evening, firstly the lower river at Glenochil:

The gauge on the lower river was showing a steady rise in river level to about a foot (and is still rising when I last checked). Now the gauge downstream of Castlehill Reservoir

Despite at least an inch of rain the change of level is measured in millimetres.

Now compare these with two other Ochils related SEPA gauges, firstly the Allan Water at Kinbuck:

and the North Quiech at Lathro, near Milnathort (a major feeder burn of Loch Leven):

Both the Allan Water and the North Quiech have much quicker responses to rainfall and generate much larger spates despite having very similar catchments. The explanation of the difference is of course simple.

Scottish Water

The headwaters of the river are effectively impounded by Castlehill Reservoir. It acts as a strategic reserve (it has to be pumped to the Glendevon WTW, while all the other reservoirs deliver water for treatment by gravity). I guess during the prolonged dry spell water is held in the upper reservoirs while Scottish Water draw down Castlehill to maintain their legal obligation to provide compensation flows to the river.   Anyone passing Castlehill Reservoir will realise just how low the water level is (I understand that they have had to suspend fishing there for moment). It will take a lot of rainfall to fill the reservoir to a level where it will be discharging over the spillways to increase the flows above compensation flow.

One of the unusual feature of the Devon below Castlehill is that there are very few feeder burns of note until the Gairney Burn is reached below the Cauldron Linn (there is the Glendey Burn in Dunning Glen, the Thorney Burn which joins the mill lade at Crook of Devon and a wee burn at the top of Rumbling Bridge). Most of the drainage from surrounding fields is lost to groundwater flows (including part of the compensation flow) to reappear in the river away downstream. At these times spates in the lower river  are much less significant then on surrounding waters as the additional water is generated by flows from the Gairney and the main Hillfoot burns only.

The impact of abstraction therefore has a significant impact on the river basin:

  • The upper river, pretty much all the way above the Cauldron Linn remains clean during rainfall events unless Castlehill is over topping.
  • The prolonged steady flows of compensation water results in excessive sedimentation which has a consequential impacts on the riparian environment
  • Part of the compensation flow is lost to groundwater flows
  • The lower river is far less sensitive to rainfall events than neighbouring rivers restricting access and opportunity for migratory fish entering the river.

So I can predict that below the Cauldron Linn tomorrow there will be a decent spate and the river will pretty dirty. I think with the continuing heavy rain overnight the Glendey Burn, field drains and groundwater will raise the upper river above the Cauldron Linn a good deal, clearing the accumulated sediment quickly ……… fishable possibly but if I had to fish tomorrow I would head to Glenquey!

Will this bring some Slob or  Sea Trout into the river?

Advertisements
This entry was posted in River fishing, River journal. Bookmark the permalink.

5 Responses to A summer spate …….. maybe?

  1. Graham Halliday says:

    I fished up from Fossoway bridge on Friday 23.6.17 . Plenty of trout, eager to grab my team of spiders – size 18’s.An olive/yellow spider was their favourite. Nothing big, but about a dozen fish from tiddlers to 3/4 lb. I have never fished up from the bridge before – some cracking big pools and runs – more water than there is down below the bridge. Overhanging branches aplenty, but still room for my wee 6′ fly rod and 4 line. Shame about the mess on the bank where the idiots camp. Burned out instant barbecues, Buckie bottles, one tent thrown in the river, another in a heap by their fire and a car battery – which I managed to lift out of the river and dump far away from the bank. They had put a load of rubbish into a big rubbish bag, but had then left the lot on the river bank – a sad sight. I suspect they were probably fishing too – at two big deep pools. The East bank from the bridge up was easiest access, but once you are away from the bridge there are numerous places to wade across with waders. Three or four very large pools just above the fish farm – great fun.

    • Graham says:

      Well done Graham, its a great bit of water particularly for the angler armed with a wee rod. The work party went through the whole section between the two bridges and cleared the worst of the overhanging vegetation during the winter but such is the importance of this section of the river as a nursery for juvenile fish it is important than plent of cover from predators remains 🙂 One thing to look out for up there is stonefly hatches, I have seen some absolutely enormous stoneflies at the tails of some of the bigger pools!

      The wild camping in Dunning Glen is a reaccuring blight in particularly the repeated anti-social behavior, massed parking, vandalism and appalling litter. The DAA have in the past cleared the whole area (one sweep generated well over 100 black bags of litter) to find weeks later the whole site covered in burnt out tents, cans, bottles and other crap. We participated in multi-party working party (DAA, Perth and Kinross Council, Fossoway Community Council, Police and the landowners) to endeavour to address the issue, but there is little than can be done to stop it. The main outcomes have been more regular patrolling by Police Scotland and the site being cleared by the Community Payback Team fairly regularly. Last years vandalism to the Dunning Glen bridge (pushing the coping stones into the river) has once again brought the problem into the focus of local councillors and Fossoway CC. Its a shame ……. it used to be a very popular picnic spot and place for kids to play in the river

  2. Graham says:

    Clearing down nicely now at Taits Tomb. A small hatch on but very few fish moving. Still sick with gills full of mud I suppose.
    Water should be perfect by tomorrow.
    Maybe some sea trout in now ?

    • Graham says:

      I came home via Vicars and Fossoway Bridges tonight; compared to this morning the river at Vicars Bridge had thinned out quite a bit and had lost its milky coffee look. At 6am at Fossoway the river had been up a good few inches and was tinged with some colour, but by home time had settled down quite a bit 🙂

      It looks like we may get another 1″ or so of rain in the next few days …….. so it may be worth trying for migratory fish (I see Cailean contacted a big salmon on the Carron today) but I suspect by the weekend I will be out with the dry flies!

  3. Cailean Moore says:

    A brilliant post. Thanks for sharing.

Leave a Reply

Fill in your details below or click an icon to log in:

WordPress.com Logo

You are commenting using your WordPress.com account. Log Out / Change )

Twitter picture

You are commenting using your Twitter account. Log Out / Change )

Facebook photo

You are commenting using your Facebook account. Log Out / Change )

Google+ photo

You are commenting using your Google+ account. Log Out / Change )

Connecting to %s