River Truim transects

Last Friday Steve and myself went up the Dalwhinnie to record some transects (cross sections) of the Truim. The purpose was to collect baseline data for the Truim in advance of the  SEPA decision on the Scottish and Southern application to remove the compensation flow in the river.  The transects involved measuring the depth, substrate and flow velocity every 50cm across the width of the river. All transects were marked with wooded stakes so that they could be repeated in future.

Before establishing the transects we recorded the water level at the compensation flow gauge. It was 0.44m, slightly above the compensation flow level, but as good as we could expect at this time of year.

When selecting our transects we were looking for sites exhibiting a range of characteristics, e.g. width, depth, flow etc so that the impacts of any future changes in river flows would be apparent across a range of habitats.

Transect TR1 at Dalwhinnie electrical sub-station

Transect TR1 at Dalwhinnie electrical sub-station. The tape measure was secured to the wooden stakes at the 1m mark with all measurements recorded in reference to that point. The width of the river at site TR1 was 10.83m. The maximum depth was 0.3m and the maximum flow velocity was 109cm/sec.

The results from each transect are displayed below in a graph showing the depth and water velocity. Unfortunately it is not possible to present wide images on the blog so apologies if they are difficult to read. The depths at this transect were relatively consistent.

TR1 transect water depth

TR1 transect water depth

River flow velocity at TR1. The darker the shading the faster the flow.

River flow velocity at TR1. The darker the shading the faster the flow. Five categories were used, 0-25cm/s. 25-50cm/s, 50-75cm/s, 75-100cm/s and 100cm/s plus. The velocities were spot readings taken every 50cm therefore boulders, divots or any others form of obstruction could influence the flow locally. The flow at this site were characterised by faster flows midstream with slower flows in the margins.

Steve recording water velocity with the RAFTS flow meter.

Steve recording water velocity with the flow meter which we currently have on loan from RAFTS.

The second site was the widest at 17.6m. An electricity power pole was used as the reference point on the left hand bank. All measurements were taken from the left bank.

Site TR2. This was a wide and shallow transect with a small "island" 7m out from the left bank.

Site TR2. This was a wide and shallow transect with a small “island” 7m out from the left bank. Between the island and left bank the water depths were shallower, below 0.15m, and water speeds were slower.

Transect TR2 depths

Transect TR2 depths

TR2 flow velocities

TR2 flow velocities

The third transect was established opposite Dalwhinnie Distillery, close to one of our electrofishing sites.

Site TR3, this was the narrowest and deepest transect.

Site TR3, this was the narrowest and deepest transect. Close to the right bank the depths were 0.4 to 0.6m.

TR3  river depth

Flow velocities were the slowest on average - slow water flow deep!

Flow velocities were the slowest on average – slow waters flow deep!

The Truim in the vicinity of Dalwhinnie had been dredged in the not too distant past and as a result has become highly mobile upstream of the distillery.

Braided section of the Truim above the distillery

Braided section of the Truim above the distillery.

One of Scotland's, and Japan's, finest products

One of Scotland’s, and Japan’s, finest products

Transect 4 was a short drive downstream of Dalwhinnie in a typical part of the river with pool and riffle sequences. The transect was established close to the tail of one pool.

Site TR4 downstream of Dalwhinnie

Site TR4 downstream of Dalwhinnie

This site was 12.17m wide on the day, generally shallow with a deeper run close to the left bank.

This site was 12.17m wide on the day, generally shallow with a deeper run close to the left bank.

Flow velocities were highest on the left hand side decreasing towards the shallower right bank

Flow velocities were highest on the left hand side decreasing towards the shallower right bank

The last site was downstream of a concrete bridge just above the Cuaich confluence. We completed an electrofishing survey here last summer.

Lower transect TR5. Where Steve was standing the flow velocity was about 1m/sec.

Lower transect TR5. Where Steve was standing the flow velocity was about 1m/sec.

TR5 water depths.

TR5 water depths. Here the flow favoured the right bank with a shallower zone on the left side of the channel.

The flow was fastest on the right at this site. !m/sec looks like a good flow for parr in the summer.

The flow was fastest on the right at this site. 1m/sec looks like a good flow for parr in the summer.

 

There was a water vole next to our transect, good to know they are doing well in this part of the Spey.

There was a water vole burrow next to this transect. Apparently the Truim supports a healthy population.

We had intended to do another transect downstream of the Cuaich but there was a much higher flow in the Truim compared to normal so we left it for another day.

The Cuaich/Truim confluence. The Cuaich was contributing about 255 of the flow.

The Cuaich/Truim confluence. The Cuaich was contributing about 25% of the total flow.

The heck gates were secured in a lifted position, presumably because no salmon would be expected to run up the Cuaich so early in the year.

Cuaich heck gates were lifted

Cuaich heck gates in lifted position. Surveys have shown that multiple year classes of salmon are present upstream of the heck so the gates are not that effective anyway.

the lower Cuaich has been significantly over-widened by dredging; an issue that may need attention if a full time flow is restored in the Cuaich.

The lower Cuaich has been significantly over-widened by dredging; an issue that may need attention if a full time flow is restored in the Cuaich.

The data collected during these transects may prove to be very useful when decisions affecting the quality and quantity of juvenile salmonid habitat in the Truim are discussed.

It was good to get out of the office again although the weather at Dalwhinnie was quite different to the mild sunny conditions that we left behind at Knockando. It really has a been a remarkably good winter in Morayshire; dry almost every day, mild and no lying snow this year. Thankfully in the upper catchment things are quite different with the snow lying thick on the hills.

 

 

 

 

 

Authored by: Brian Shaw

There are 2 comments for this article
  1. Donald Gordon at 3:32 pm

    10/8/2019
    Are salmon still able to access the truim upstream of truim dam. The fish pass was choked with gravel.

    • Brian Shaw Author at 5:43 pm

      Hi Donald, yes, although I have not been to the locality recently. I am aware there there has been a lot of gravel management going on but one of my colleagues has been liaising with SSE. I am sure that fish passage has been preserved. There were good numbers of juveniles above the dam last year.

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