OCTA, Caltrans and OC Supervisors urged drivers to avoid the area entirely during that twenty hour period, but if travel from southern L.A. County to OC or vice versa is absolutely necessary, to use alternate routes of their own design, or follow official detours (map below) and allow time for any delays.

To view the news conference, click here or on video icon below.

Orange County Supervisor John Moorlach noted that a predicted "Carmageddon" didn't materialize during a weekend closure of the 405 freeway in the Sepulveda Pass because drivers stayed away and used alternate routes...and he urged local residents to likewise stay away or apply their knowledge of area streets and freeways to devise creative ways around the twenty hour 405 closure.

Below is a map showing OCTA's suggested detours. Click the image below to display zoom-able pdf.

And here's a Google detour map display:
View WCC Closures: Monday, August 12 - Sunday, August 18, 2013 in a larger map

The maps are confusing to us; we can think of plenty of other ways offhand to circumvent the temporary closure. The best one is to avoid the trip entirely if you can.

There's further information on the OCTA link here.

Bottom line: the 405 will entirely closed from the 605 to Valley View St. in both directions from Saturday at 9 p.m. to Sunday at 5 p.m. Don't go through that area during the twenty hour bridge removal period if you can avoid it, or if you have to, use your head and use an alternate route.