Management Produced by Emergency Management Australia Vol 15 No 4 Summer 2000-2001 In this issue... % Cost-effective spillway designheview for small dams in Victoria: avoiding dam failure emergenciesy by Dr John D. Pisanielio, Wrof Jennifer M. Mckay and Mr Siraj Perem Tasman Bridge disaster: 25fianniversary memorial service $29 by Rod McGee and Lynn Young vh Understanding employee responses to disaster 3uc\'y by Thomas E. Dmbek "1 Community mapping-an aid to emergency management 3uc CAY by Rick McRae and Alan Walker vh Landslips-a moving story (a Municipality's perspective) $25 by Lex Ritchie & Glenn Hunt vh East Timor-emergency risk management $25 by ~gtnlr Turketo "1 New guidelines aim to support older people in emergencies %$ by Lesley-Anne Knight "1 Lines that divide, ties that bind: race, class, and gender in 3 C women's flood recovery in the US and UK by Elaine Enanon and Maureen Fordham 3 The Brisbane-Gladstone transport corridor: identification of risk KAYC and vulnerability for the bulk transport of dangerous goods by lmphne R.W. Childs,Ralph D. Carlisie, and Peter A. Hastings vh Direct and vicarious experience of volcanic hazards: 3csCKAY implications for risk perception and adjustment adoption by Douglas Paton, David M. Johnston, Mark S. Bebbington, Chin-Diew Lai and Bmce F. Houghton Plus ... Book reviews 53 Conferences and other announcements 8, 32, 36, 42, 52, 57, 63, 64 Disaster Events calendar 64, 65 EMA Update Centre pages Cover: Spatial data collection at a local level (community mapping) can be used to fill the gap between available datasets and those required by emergency managers. st-effective spillway designlreview for small dams in Victoria: avoiding dam failure emergencies Introduction A clear need has developed for a Australia has a large number of relatively by Dr John D. Pisaniello, BE (Hons I), mechanism that: small, privately owned dams (farm dams raises public awareness of this problem PhD, Research Fellow; AIProf Jennifer M. in particular): those which have failed and improves the transparency of the number in the thousands (ANCOLD Mckay, BA (Hons), LLB, PhD, GDLP, risks 1992). A large proportion of these dams Associate Professor in Business Law, promotes consistency and uniform are located in Victoria which has an University of South Australia, School of standards estimated 170,000 farm dams, 800 of International Business, Water Policy and simplifies the engineering desiglreview which are large enough to cause serious Law Group; Mr Siraj Perem, MSc. processes involved while keeping in line consequences downstream if they failed MIEAust, MICE, Water Assets Engineer, with state-of-the-art practice (ANCOLD 1992; Murley 1987).Thegrowth Dept. Natural Resources and minimises reviewldesign costs to of farm dams in Victoria (and Australia) Environment, Victoria. private owners and in turn encourages is also increasing at a rapid rate. For better dam safety management example, in the Victorian Lal Lal Reservoir The Department of Environment and catchment alone (234 kd), farm dams Natural Resources, Victoria, recognising increased in number from 182 in 1970 to identified many unsafe, hazardous private this need commissioned the University 534 in 1985, representing an increase of reservoirs and found that most owners of South Australia to undertake a study about 200% (GHD 1987). When thesedams are not taking the necessary action in based on Pisaniello (1997 PhD thesis, see were constructed, the majority more than terms of analysis and upgrading of their also Pisaniello et al 1999), in order to 20 years ago, their designs were based on structures. establish such a mechanism for Victoria. rainfall frequencies and intensities, design Consequently, the recognition of risks This paper summarises the preliminary methods and criteria and standardsofrisk associated with the dams has increased procedures involved in the study, presents available at that time. However, these greatly. A need has therefore developed the resulting cost-effective flood capa- aspects have changed over time, together for private dams and risk to co-exist and bility designlreview procedure, and with population distributions and the for owners to appropriately manage their provides worked examples of how to condition of the dams, raisine serious dams in line with current standards in amlv the ~rocedure. ., 8.f doubts about dam adequacy. order to reduce the risks involved, reflect The development process In modern times, the major concern community standards and provide in- The Pisaniello (1997) procedure primarily with dam safety world-wide is the pro- creased dam safety assurance to down- involves the development of regionalised vision of adequate spillway flood capa- stream communities. flood capability prediction relationships bility. This is mainly because significant In particular, owners should review the for dams on small rural catchments based advances made in the fields of meteorology spillway flood capabilities of their dams, on the Reservoir Catchment Ratio (RCR): and flood hydrology have updated both and upgrade if necessary, in order to avoid maximum drobabk rainfalls and design liabilityfor possible faiiure consequences floodstandardsabove thoseon which most (McKay and Pisaniello 1995). Unfor- existing dams were based. As a result of tunately, the engineering processes these revisions, many dams have in- involved are highly rigorous and time- sufficient spillway capacities. consuming in practice and therefore In addition to this concern is the fact generate high consulting fees which in that most private owners hire contractors many cases are not affordable by private (Equation 1) toconstruct their dams. These contractors owners. For this reason, owners tend to are, typically, not properly trained or overlook the need for reviewing their where: skilled in the design and construction of dams and instead develop a sense of SC = spillway overflow capacity (m3ls) dams. Thus, many private dams are not complacency, believing that as the dams PIpMF= peak inflow for the PMP design built to an adequate standard. For have not failed up to now, then they will flood event (m31s) example, the layers of soil that constitute never fail. In essence, owners lack an RA = resenroirarea at Full Supply Level (km2) the dams are not properly compacted and appreciation of the risk of failure to SH = maximum height of spillway the structures are not provided with society and the costs. The result is that overflow (m) adequate outlet works. This is evidenced dams are deprived of necessary upgrading CA = catchment area (km2) by a recent case study investigating and downstream communities are placed = peak inflow for the 100 year ARI private dam safety management practices at risk. Pisaniello &McKay (1998) demon- event (m31s) in South Australia (Pisaniello 1997,seealso strate the potential seriousness of this PISo = peak inflow for the 50 year ARI Pisaniello and McKay 1998). The study problem. event (m31s) 2 Australian Journal of Emergency Management For regions where no variation is (AR&R) (IEAust 1987 and new edition) Producing a design peak flow pre- observed in the Annual Exceedance and Bulletin 53 (BoM 1994). diction equation for the PMF event, ie. Probability (AEP) of the Probable Maxi- The calibration flood studies basically scatter plot of catchment area (km2) mum Precipitation (PMP), the RCR can involved: versus peak flow (m'ls) in the logarith- take on the compact form: collation of recorded streamflow, daily mic domain. This equation when rainfall and pluviograph data substituted into the RCR establishes a RORB catchment modelling Regionalised Reservoir Catchment trial-and-error 'fitting' of modelled Ratio (RRCR). hydrographs with recorded hydro- Using the determined peak inflows and graphs elevations to establish peak inflow- (Equation 2) SMEC Victoria was commissioned by frequency and elevation-frequency the University of SA to perform the relationships for each dam. With these Developing the RCR, based on the calibration study for the Barringo Creek relationships the Imminent Failure Pisaniello (1997) procedure, necessitates catchment in order to provide a basis for Flood (IFF) capability of each dam is the collection and derivation of approp- independent comparison and check. determined as IIAEP (years). The IFF riate 'calibrated' catchment and reservoir In order to create the flood capability is taken as the smallest flood which data in the study region, and the formu- prediction relationships, it was necessary peaks at the lowest point of the non- lation of a range of hypothetical dams to produce a wide range of flood capa- overflow crest (ANCOLD 1986): this is (approximately 20) on each catchment bility outcomes relating to embankment in line with the ANCOLD (2000) defi- representing all possible scenarios up to dams placed at the outlets of the regional nition of Dam Crest Flood (DCF) for the PMP design flood event. calibrated catchments. The aim of the embankment dams. It should be noted An initial search for appropriate process is to represent the hydraulic that ANCOLD (2000) defines IFF as'the 'calibrated' data for rural catchments up response of any size of reservoir and flood event that could be reasonably to lOOkm2 proved unsuccessful. SMEC spillway(s) relative to the hydrological expected to cause failure of the dam', Victoria was then commissioned by the flood response of the selected 'catchment and hence, for the purposes of this University to undertake a more detailed type' (Pisaniello 1997). In brief, this was paper