I wanted a wadi for WWII North African Desert games so I made one. It took a while to figure out the best method to get what I wanted but I got there in the end. It took much longer to figure out how to make them than the actual making itself. All up they took about a week and most of that time was spent waiting for things to dry and cure.
Lots of photos and details on how I made it on my blog at: http://this28mmlife.blogspot.com/2021/06/making-wadi-shawaddywaddy.html
(https://1.bp.blogspot.com/-RmP2RYxHtbc/YM2UkF_SPsI/AAAAAAAAfXY/q1A0_YZhM00UUcXRy2JmJAVO6TIEYucTACNcBGAsYHQ/s800/Wadi_20.jpg)
(https://1.bp.blogspot.com/-WS-ymCXjr5E/YM2Uh3SaJTI/AAAAAAAAfW8/mJ8dp6e4vGwATQ7siTVDSPcOo_kuBkqmgCNcBGAsYHQ/s800/Wadi_16.jpg)