How to create DEM using LiDAR ASCII GRID files

[SamKwan]

I am new user of ArcGIS and need to create a DEM for flood mapping using LiDAR data. I downloaded a few hundreds of LiDAR asc files but dont know how to create the model.  Should I use ASCII to raster?! But each time I can only convert one asc file.

Second question is: after conversion, a folder containing the raster file is created. So if I convert all the asc, I will have a few hundreds of folder for the raster files. My question is how I can combine all the raster into one DEM for further analysis? 

Thank you.... urgent pls!!

[TimothyHales]

The ASCII to Raster tool should work for you to convert it to raster.  You can do more than one file by using the batch mode.  This can be found by right clicking the tool in ArcToolbox and choosing the 'Batch' option.  Here you can right click the input of the matrix and select all of the asc files by browsing to them. 

Or, with ArcGIS 10 you can create a model with an iterator.  You will want to the the Iterate Raster iterator and specify an 'in-line variable substitution'.  Here are some example of using iterators in ModelBuilder. 

As for the folders, it sounds like you are using GRID as the output format.  Its structure is made up of a lot of files within a folder.  If you have hundreds of GRID outputs, then there will be hundreds of folders.  You can specify another output format such as TIFF or IMG by changing the output extension.

[JeffreySwain]

I would continue with what Tim said and consider creating a series of multi point files in a geodatabase feature dataset with the Ascii to 3d Feature Class.  Once the files are in the feature Dataset, then you can create a terrain with them and then eventually convert the terrain to a raster if you so desire.

Be sure to use the point file information tool, prior to running the two tools to obtain the point spacing.  

There are a great series of blog posts discussing terrain workflows.