PowerShell : Delete All Site Collection Present Under Web Application

#check to see if the PowerShell Snapin is added
if ( (Get-PSSnapin -Name "Microsoft.SharePoint.PowerShell" -ErrorAction SilentlyContinue) -eq $null )
{
    Add-PsSnapin "Microsoft.SharePoint.PowerShell"
}

Start-SPAssignment -Global

function DeleteAllSiteCollections([string]$url)
{
    try
    {
        $webApp = Get-SPWebApplication $url
        foreach($siteCol in $webApp.Sites)
        {
            Remove-SPSite –Identity $siteCol.Url –GradualDelete –Confirm:$False
            Write-Host "Successfully removed the site: " $siteCol.Url -ForegroundColor Green
        }
    }
    catch [System.Exception]{ Write-Host $_.Exception.ToString()}
}


$webAppUrl = Read-Host "Enter the url of the Web Application"

DeleteAllSiteCollections $webAppUrl

Stop-SPAssignment -Global