Asphalt Specialists In Hydraulic Engineering

Applications

Coastal Protection
Dam Waterproofing
Dam Erosion Protection

Dam Spillway Protection

Fordingbridge Flood Alleviation Scheme
Bodmin Town Leat
Blackmoorfoot Reservoir

Loch Ericht Refurbishment Works

Ports & Harbours
Flood Alleviation
River Training
Scour Protection
Underwater Impact Protection
Strengthening Rock Structures
Landfill Linings
Offshore Services

Loch Ericht Refurbishment Works

Introduction

Ericht CompleteLoch Ericht straddles Perthshire and Highlands Regions in Scotland, and is a natural loch drained by the River Ericht, flowing in a southerly direction into Loch Rannoch.  The loch level was first raised in 1930/31 by the construction of Ericht Dam at the south western end, and further in 1937 by the raising of Ericht Dam and construction of Dalwhinnie Dam at the north eastern end.  The reservoir is now over 24 km long, is owned and operated by Scottish & Southern Energy plc, and supplies the Rannoch hydropower station as part of the Tummel Hydro Electric scheme.

Following a statutory inspection in June 2000 under the Reservoirs Act 1975, both dams were subject to more severe design flood standards, the result of which was that the freeboard and overtopping protection was inadequate.  The refurbishment works included raising and extension of both dams, strengthening of the upstream and downstream faces at Dalwhinnie Dam, and improvements to the spillway basin at Ericht Dam.

The consultant for the works was Faber Maunsell, the main contractor was Morrison Construction Services and the asphalt works were carried out by specialist subcontractor Hesselberg Hydro. 

Design

  • Dalwhinnie & Ericht Dam – Dowstream Face & Spillway Basin

    Erosion protection was required to prevent damage during overtopping at Dalwhinnie and to reinforce the embankments within the spillway basin at Ericht.

    In both cases open concrete blocks and in-situ Grasscrete were specified to provide the erosion protection.  Hesselberg Hydro offered an alternative design using Open Stone Asphalt which provides sufficient erosion protection and a surface able to encourage the growth of plants through the material.  This was important to satisfy the aesthetic requirements for the embankments.

    During the works on the Dalwhinnie downstream face it became apparent that the embankment fill material beneath the topsoil was granular and quite loose.  During an extended overtopping event there was concern that this material would become saturated and then unstable.  To reduce the seepage of water into the embankment a layer of Lean Sand Asphalt was placed beneath the OSA.

Installation

  • Dalwhinnie DamDalwhinnie Dam – downstream face (4,500 m2)

    The existing downstream face consisted of a granular embankment covered with topsoil and vegetation.  The topsoil was stripped down to the granular material then OSA was placed over the area on a geotextile filter layer.  The placing method was similar to the upstream works but with two excavators – one at the toe and one at the crest.

    The crest road and the lower section of the slope were covered with 125mm OSA whilst the top section of the slope was covered with a 100mm layer of OSA.  The LSA layer beneath the geotextile on the higher sections was placed at 50-60mm thick over the crest and upper parts of the slope.
  • Ericht Dam – spillway basin (900 m2)

    The works at Ericht dam consisted of protecting slopes adjacent to the spillway structure, protection of the crest road at both ends of the dam, and lining of a drainage channel to take water from the crest down to the basin.

    The works were executed with a long-reach excavator placing a 125mm layer of OSA on geotextile.

 

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