This　study　attempts　to　use　a　dam　breach　model　to　reproduce　the　well-monitored　outflow　hydrograph　obtained　during　the　dam　breaching　process　of　the　Tangjiashan　barrier　lake,　which　was　formed　by　a　landslide　triggered　by　the　Wenchuan　earthquake　on　May　12,　2008　in　China.　The　key　parameters　that　affect　the　model　results,　such　as　soil　erosion　and　breach　lateral　enlargement,　are　reviewed　by　using　field　measurements　followed　by　extensive　sensitivity　studies.　The　present　paper　advocates　a　hyperbolic　model　for　soil　erosion　rate　and　a　circular　slip　surface　approach　for　breach　lateral　enlargement,　which　contribute　to　more　reliable　model　results.　The　governing　equations　are　solved　using　a　numerical　method　that　allows　straightforward　calculations　coded　in　an　Excel　2007　spreadsheet.　This　provides　an　easy,　transparent,　and　robust　tool　that　could　enable　practicing　engineers　to　perform　dam　breach　analyses　with　a　comprehensive　understanding　of　the　uncertainties　involved.　This　back　analysis　confirms　that　the　peak　outflow　can　be　predicted　with　reasonable　accuracy　if　the　input　values　of　the　key　model　parameters　are　within　well-understood　ranges.　(C)　2014　American　Society　of　Civil　Engineers.