Mason P.J.,MWH Ltd.
Dams and Reservoirs
Water availability in terms of rainfall and/or river flow tends to be analysed and predicted in probabilistic terms. That is to say historic records are analysed to produce such things as mean years and 95% wet or 95% dry years. However, there is increasing evidence to show that, on occasions, sustained periodicities appear in such records. Where this happens they can be used to supplement probabilities by better targeting which years are likely to be wet and which years are likely to be dry. The benefits in terms of planning crop yields, hydropower output, water supply and even targeting needs for famine relief are obvious. The author explores this with some examples from his own experience and that based on a talk he delivered in London on 20 February 2015 to a joint meeting of the Irrigation and Water Forum and the British Dam Society. © 2015, ICE Publishing. All rights reserved. Source
Masaon P.J.,MWH Ltd.
Proceedings of the Institution of Civil Engineers: Civil Engineering
An understanding of climate variability - both man-made and natural - is vital in the planning of major water infrastructure and other civil engineering works. While there has been extensive modelling in recent years of mankind's potential effects on climate, studies of natural variability have not been given the same prominence. in the light of wider availability of climate data and an increased ability to process such data, this paper revisits the effects of natural variability. Using African examples it shows that clear natural cycles can be identified which, when combined with possible anthropomorphic effects, can provide civil engineers with far better long-term climate predictions. Source
Modares M.,Illinois Institute of Technology |
Quiroz J.E.,Illinois Institute of Technology |
Quiroz J.E.,MWH Ltd.
International Journal of Geomechanics
Concrete-faced rockfill dams (CFRDs) are commonly built around the world. As energy demands soar and construction methods evolve, the interest in the construction of CFRDs with larger heights has increased tremendously. However, because of the construction of higher CFRDs, some dams have experienced considerable fractures at the concrete faces. Well-known cases include Campos Novos (Brazil), Barra Grande (Brazil), and Mohale (South Africa), where in some instances these cracks have led to dewatering of the reservoirs to allow for the concrete slabs' repairs. The development of these fractures may be attributed to the highly deformable rockfill body. In general, the state-of-the-art design of CFRDs is mostly based on common practice rather than rigorous analysis procedures. And as such, cracking problems because of deformability of the rockfill may not be properly predicted unless a detailed analysis is performed. In this work, a new framework for the analysis of CFRDs is developed that is capable of predicting the possible failure of a concrete facing. As part of this framework, a comprehensive nonlinear finite-element analysis scheme is developed to model the construction sequence, the contact interaction between the concrete facing and the rockfill body, and the impounding of the reservoir. As a case study, using the developed framework, the Kárahnjúkar CFRD (Iceland, 198 m in height) is analyzed, the results are validated by the field measurements, and suggestions for mitigation measures are provided. This methodology, based on the results of the investigation, provides guidelines and establishes a framework for analysis of CFRDs that can be used for design purposes. © 2015 American Society of Civil Engineers. Source
Shah S.R.A.,WAPDA |
Khan R.A.,WAPDA |
Ali M.,MJV Consultants |
Asghar N.,MJV Consultants |
And 6 more authors.
Proceedings of the Institution of Civil Engineers: Geotechnical Engineering
The Mangla dam project in Pakistan was the largest embankment dam project in the world when it was completed in 1967. The 260 km2 reservoir is formed by four major dams, each with a different cross-section, and each a significant structure. The original designs included provision for raising the dams by up to 12 m to offset the effects of future sedimentation. In 2000, capacity lost due to sedimentation became a significant issue. The government of Pakistan decided to exploit the raising provisions of the original design, and store flood water that was routinely being released. Following studies to confirm the most economic extent of raising, the original designs were reviewed and modified. Since the 1960s there have been advances in geotechnical and seismic engineering, changes in design parameters and information from 40 years' performance of the dams, all of which had to be taken into account in revisiting the designs for the raising. As a result, the dam cross-sections for the raised embankments have been adjusted using updated parameters, and the opportunity has been taken to address some areas of seepage that have been under observation since the original construction. Construction for a 9 m raise began in 2004 and was completed in December 2009. The total length of dam embankment after raising is 14 km, with a maximum height of 148 m. The work required 31 million m3 of fill materials, and is one of the largest dam-raising projects ever undertaken. Source
Mason P.J.,MWH Ltd.
International Journal on Hydropower and Dams
Much continues to be written about estimating plunge pool scour under free falling jets. The author summarizes the background to this subject with guidance and an update on the most reliable approaches to use. Source