I have watched flood waters almost reach our home twice now. I have also observed that for the most part, our planted raised bed did not flood. And the mulch stayed put?! I am thinking of making a short 18" berm to block water from heading to our house to block and redirect some water from one direction. That would redirect the water away. Some water would of course get into the berm. But all that would be left is to sand bag the walk way at the west side of the house. Do you think it would work? I would plant more Mexican Petunia so that it flanks the walk way on both sides for aesthetics, low maintenance, and to hold down the soil I would use the same mulch for continuity where it meets up with the other larger raised bed. I have purchased 24" x 50 feet long Root barrier. I could use it on the back side of the berm for added protection.

Since Mexican Petunia grow practically in any soil, what should I use under the mulch to build a berm?? I wish I could find some clay!!

Surprised that clay is difficult to locate in Houston.
Have you considered purchasing a truckload of "fill dirt"?

Sand would actually work... Once dumped in a pile, it dries out and gets hard... Impossible to get a sand berm to absorb water... Around here...

Maybe consider a swale?

I wanted to direct water away from my driveway to run down the road. I raked the sand into a long " hill" and dumped leaves and pine straw along it. Any seeds raked grew and I also dumped seeds in the mix. I'm in the woods on a " pig trail" so to speak, so it may not be pretty but keeps the water from a gully wash rain out of the driveway and side yard...works for me. My place has always been more wild kingdom rather then home and garden beautiful. Lol

I think sand would wash away and would personally advise against clay. When dry it is as hard as a rock but when saturated with water can turn into a giant slimy mess.

I think fill dirt sounds like the best plan so far, but would plant bushes with extensive rooting systems on top to hold the whole thing down. Or, another raised planter might be better yet if it will fit in that space.

Perhaps you could have some clay-based topsoil dumped along the line you drew in the photo to form the berm. Then you might plant Liriope muscari (NOT Liriope spicata, which can be very invasive) along both sides of the berm, and perhaps on top as well. Liriope muscari has an extensive root system that doesn't mind getting flooded on occasion and will hold the topsoil in place. It is happy in sun or shade. The edge of the Liriope planting that faces the lawn is easily kept in check by mowing, and the sidewalk will keep the other side in check.

Cheryl ! You have my complete sympathy and concern. I will never forget the picture of a flooded farm along the Mississippi from years ago. The farmer had pushed a huge dirt berm (I do mean Texas Size Huge) around his farmhouse and then parked the dozer on top of the berm. The berm, the dozer & his home were the only dry spot visable for miles in this aerial picture. The scene took my breath away. His berm was all top soil.