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<br />tJooK VI ~ t::sttmatlon Of Large to ~reme t'looas
<br />
<br />Book VI
<br />
<br />Estimation of Large
<br />to Extreme Floods
<br />
<br />R J Nathan and P E Weinmann
<br />
<br />1 Introduction ....."'..'.."m..............."...........,....,......,......,...,.,..,....,,......'..m'_'.............'..'..'..'...._..'..'m'..' 1
<br />1.1 Scope and Intention ofthe Guidelines ..m...m..........m........'........'......m'............m.........m..mm....'....' 1
<br />1,2 Applications Covered by These Guidelines,..........m,......,....,...._,......,............................m...m,m........1
<br />1,3 Overall Design Approach Adopted ""....,.."......"..,.."..,_,..,.."........'........,...,_..""...."...."m'........_...... 1
<br />1.4 Relationship with Other Sections of ARR....m.......'..'....'..m....'....m.."..'....,....,......_,....,..............mm.. 3
<br />
<br />2 Procedures for Estimating Large to Extreme Floods.......'......mm..........._.~..................A
<br />
<br />2,1 Summary of Procedures ,..,m,...,.."... "......,......"..,.........,......,...'..._". ..,....",....,..",.., "".."..,,'..'..','...,.. 4
<br />22 Theoretical and Practical Implications of the Procedures m........m........'...............,..........m..m..m...... 4
<br />2,3 Relevance of Procedures to Specific Applications,....m...........,......,...._,............................................. 7
<br />
<br />3
<br />
<br />Estimation of Design Rainfalls..""..............",.....,.,_".....,...".,..."..,......,,..,..,..,,'.......'....,...........m. 8
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<br />3,1 General ,'..,........,..,'..'......""_"..,....",......"'m..".._....,,...................'.......,..."...,..,..""'m......'..'"....,....'. 8
<br />3.2 Estimation of Design Rainfalls with an AEP Between 1 in 50 and 1 in 100 ......m................'..........m.. 9
<br />3,3 Extrapolation of Rainfalls to the Credible Limit ..m............m......m..'....'m...........m'm......'m..m..'..m 10
<br />3,3,1 Areas without specific regional design information ..................m....'m.._..m'........mm...... 10
<br />3,32 Areas with regional design rainfall information..........................mm....m..........,......m,...... 10
<br />3.4 Estimation of the PMP Depth ..................m..........................'..'m....'....,........'..m..m'm...................... 11
<br />3.4,1 GeneraL.." m..,.. ,...."...."",.. _.."..,.."'.....,............_.........., ..m........'" ,.. _,.......... ,.. ........ ,...... 11
<br />3.4.2 Small areas and short durations..............................._..,......................,...._,.....m..............13
<br />3.4.3 Longer durations in Southeast Australia m....m..................................'...........................m 13
<br />3.4.4 Longer durations in Tropical Areas ....................'..m'..m'....m..m..m'....'......._.................. 13
<br />3.4,5 Longer durations in the Transition Zone.m....m....,m..,.........,..,............,..............,_,.....m..14
<br />3.4.6 Intermediate Durations .m..........'..........",..,..,...,.','................. m ,_, ,....,.. ,..,..,..........,......,'.. 14
<br />3,5 Assigning an AEP to the PMP ......................m.............m......uu'.....,....,u............'...........m.._'..mm.. 14
<br />3.6 Rainfalls Between the Credible Limit of Extrapolation and the PMP ......................m'm......'....,......... 16
<br />3,6,1 InterpDlation between 1 in 100 AEP and the PMP when no Rare regional estimates
<br />are available for any durations ......'m..............................,......................_......m....'...........16
<br />3.6.2 Interpolation between the credible limit of extrapolation and the PMP when Rare
<br />estimates are available,....,..m....m...m,..m......",..,....,..,....................................,.......'...m,18
<br />3,6,3 Extrapolation of regional design information to other durations ....................................m.19
<br />3,7 Seasonal Estimates of Large to Extreme Rainfalls................................,...........................................20
<br />3,8 Large to Extreme Rainfalls fDr Very Long Durations ........m..'..'...............................'..'..m................ 21
<br />3. 9 Temporal Patlems..,.... ,.................................................'.. ....,......"............. ,......,..............., ,.... ..........,22
<br />3,9.1 GeneraL,.." m..m" ,............,.. ,.......... ..... ....,..........,............. ....,..,......, ,_, m................""..,.' 22
<br />3,9,2 Specific Recommendations, ......' ........... .....'.,... ............,... ,.."....,.. m.. _ ,........,......,....,..,..,.. 23
<br />3,10 Spatial Patlerns..m....m,..,.."..,........."..,......,.............,..,..........................m.........m.........m....'....'.._, 23
<br />3,11 Preliminary Estimates of PMP '..........mm..'m....'..'_'..mm......'..'..,.....................................................24
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<br />4
<br />
<br />Estimation of Design Floods"",.",."..,....,..........,..,..,..,......"""..........'..m..,..",..........'..'....'m'..'.. 24
<br />4,1 General Approach,.... m..'.... m.. ......""...............,...,.., ,.., m.. _......,................. ,.. m_....'... '....,....... '....m 24
<br />4,2 Losses and Rainfall Excess "........,............"",....,"......'m........"....,..,_,.........'.........,.m.'...'..'m"..'.... 26
<br />42,1 General considerations ",.',..................'.....mm.....m..'................,..,............,'.....'........m'.. 26
<br />422 Methods for derivation of design IDSS values ........................m...._..m.........m...........'...... 28
<br />42,3 Guidelines for selection of design loss values ..............m......'..........'.............................. 28
<br />4.3 Hydrograph Models..,..,..,..,..,..",.." ,..,... _ ......,..".. ,........ m'........',......,..,."............. _,......., m.. m .........,31
<br />4,3,1 GeneraL....,....,...........,.."", ,_,.."..".. m..........'" ....",........",.... '....,..",.. _ .........,............ ,...... 31
<br />4,3,2 Model features and capabiiities..,...."..,m".......,..".._,......,..,.,......,..,.........,..........."....,..,..31
<br />4,3,3 Catchment representation in model.................m..........._....,........m........m....m........m.... 32
<br />4,3.4 Determination of model parameter values ......m........m......'................'m........'...m._....... 32
<br />4,3,5 Specific recommendations for runoff routing models--................................,..............,......33
<br />4,3,6 Specific recommendations for unit hydrograph models m...'.........mm....'...._..'......'..m....34
<br />4.4 Baseflow ,..",""'"'''''''''''' ,,', ..,.....,.... "...."'..""".._..".."..,.."'..,.."..,.."...'..m.'....".." .......,..,..,..,.....",34
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