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Dams and Spillways

Reinforced Rockfill for Construction Flood Control – PJ Pells, 1978 [1.15 MB]

Three dams (Bridle Drive, Lesapi, and Xonxa) were constructed in southern Africa between 1970 and 1975 making use of downstream zones of reinforced rockfill to control major construction floods. In the cases of the Bridle Drift and Lesapi dams relatively minor failures occurred when floods passed over the partly constructed embankments, while at Xonxa a major failure occurred.  From these failures and from the successful performance of the Googong dam, completed in 1978 near Canberra, conclusions are drawn regarding the important factors to be considered in the design and construction of reinforced rockfill dams of this type.

Damage and cracking of embankment dams by earthquake and the implications for internal erosion and piping  – S E Pells and R Fell, 2003 [740 KB]

As part of Steven’s masters, he was supervised by Prof. Robin Fell in reviewing case studies of cracking of embankment dams from earthquakes.  It was a desktop study but based on this literature a long database was formed which collated parameters on the documented damage and the earthquake characteristics.  Trends in these observations were plotted and provide a first pass assessment of possible damage based on earthquake magnitude and peak ground acceleration.  

Erosion of unlined spillways in rock – Does a ‘Scour Threshold’ exist? – SE Pells, PJN Pells, WL Peirson, K Douglas and R Fell 2015 [588 KB]

An early paper during Steven’s PhD, a perhaps less tactful appraisal of published methods for assessment of rock scour.  

Assessment and surveillance of erosion risk in unlined spillways – SE Pells, SANCOLD 2016 [2.45 MB]

A guide to assessing erosion risk in unlined spillways.

A Tale of Two Spillways – PJN Pells, SE Pells and M van Schalkwyk, SANCOLD 2016 [1.17 MB]

Steven and Philip Pells travelled to South Africa in 2014 to review some spillways and were accompanied by Prof. Monty van Schalkwyk to view the remarkable erosion damage to Mokolo Dam.  The similarities to the erosion at Copeton Dam, Australia captured Philip’s curiosity, giving rise to this short paper.

Guidelines for assessment of scour in unlined spillwaysSE Pells and K Douglas, 2019 [2.25MB]

Steven and Philip Pells had drafted a flowchart setting out how to assess rock mass erosion.  This paper steps through the flowchart with guidance and rationale for each step.

Guidance on the calculation of stream power dissipation for rock scour assessmentsSE Pells, WL Peirson, F Al-Qassab, 2019 [3.57MB]

Various published methods for assessing scour of rock use stream power dissipation as an index of hydraulic erosive power. This paper presents recommended procedures for calculation of stream power dissipation to ensure compatibility with these published methods. Discussion on the usage of CFD modelling results in these comparative erosion assessments is also provided.

Erosion of rock in spillways – SE Pells PhD, 2016

Steven Pells PhD can be accessed here.

The legacy and potential of Junction Reefs Dam – SE Pells and PJN Pells, 2017

This paper was really an interest piece that arose out of Philip Pells unquenchable curiosity.  The 120 year old multiple arch brick dam was the first of its kind in Australia and piqued Philips interest.  We tramped through the bush on a number of occasions to visit it, found old rusted relics of its ancient but ill-fated hydro-scheme, trialed the (then) new technology of UAV photogrammetry, re-examined its stability, mapped the spillway and undertook a hydrological study to estimate its hydro-energy potential – all just for fun. We published a paper summarising some of this work at the ANCOLD conference in Hobart in 2017.  I had made a bad error in presenting its hydropower potential, which I have rectified in the attached version.

The influence of geological conditions on erosion of unlined spillways in rock – Douglas, K., Pells, S.E., Fell, R., Peirson, W.L.  2018 [5.8MB]

This paper presents the Rock Mass Erosion Index (RMEI), which is a rock mass index developed to characterise the presence of kinematically feasible mechanisms in a rock mass that create vulnerability to erosion.


In 2017 Steven Pells and Kurt Douglas attended an international workshop on behalf of the European Group of ICOLD and French Committee on Dams and Reservoirs, held at the small town of Aussois in France.  This document was submitted as a chapter for a book that was to be issued following the conference. This chapter provides a overview of scour assessment techniques that had arisen as part of my PhD studies, and projects I has worked on at that time, and includes some worked examples. I am unsure of its publication status, so when prompted to, I have cited it as: PELLS, S.E and DOUGLAS, K. (in publication) Hydro-geotechnical assessment of scour of rock. Book chapter from an international workshop on behalf of the European Group of ICOLD and the French Committee on Dams and Reservoirs, Aussois, France, 11th to 14th December 2017. 

Rock mass erodibility –  PELLS, S., DOUGLAS, K., PELLS, P.J.N., FELL, R., PEIRSON, W.L. (2017)

The usage of the Geological Strength Index (GSI) was examined in my PhD regarding its efficacy in characterising erodibility of rock masses.  With a small modification this gave rise to the Erodibility Geological Strength Index (eGSI) which  was found to be a useful predictor of rock mass erodibility, as presented in this paper.

Copeton Dam: Performance of the Great Scour Case Study in the floods of 2022 – Pells, S.E., Duwell, A., Parmar, H. 2023

The spillway of Copeton Dam in New South Wales suffered massive and unexpected erosion in the 1970’s and has been a widely discussed case study because of this.  In 2022 the service spillway operated for the first time in 40 years, to considerable anticipation.  I was delighted to be able to view the spillway firsthand after this spill, and presented some of the findings in this paper at the ANCOLD conference in Cairns, Queensland, Australia in November 2023.

Hydro-geotechnical rock scour assessment at Petit-Saut Dam. – PELLS, S.E., AL-QASSAB, F., WEIR, F., FAIVRE, A., LETURCQ, T., BLANCHER, B  (2022)

Petit-Saut Dam is a hydropower facility in French Guiana, and significant erosion has been developing below some of the outlet chutes.  An excellent bathymetric survey was key in diagnosing the erosion process, along with some detailed hydrodynamic modelling.  Some of the details of this case study were presented at the 4th International Seminar on Dam Protections against Overtopping (“Protections 2022”) in Madrid, Spain, 30 Nov to 2 Dec 2022.


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