Raised bed hands down. Even if there wasn't a problem with flooding I would reccomend raised bed. My soil is black clay that turns to chewing gum when wet,doesn't purculate water well at all, takes forever to dry then cracks and becomes hard as brick. I build raised beds and and mounds using a method known as hugelkulter.

Not many here even know it exists so you should seek a group that is into it. My suggestions are (A) never use walnut,white oak,cedar,juniper or bois-d-arc (B) Use wood that is 90% rotted and/or compost mixed with native soil in top 8". From 8" below surface through next 8" use wood showing rot mixed with unfinish meterail suitable for composting (saw dust,leaves,grass clippings,twigs,cardboard ect mixed with

high nitrogen material. From there down as deep as you care for, wood can be but doesn't have to be rotten but I reccomend wood which has low resistance to rot (in my area Hackberry is abundant and rots very quick. Be sure to fill cracks and voids with soil and/or other fines between material as it is layered.

The cavet is beds aren't very productive first year unless you are carful to have a nice upper 12 or more inches of soil. Where it really shines is drains exelent AND retains perfect level of moisture 4x as long as surrounding soil.

Every french drain I've saw collected junk until it no longer drained. 5 years at best.

Klem1, Thank you for information on Hugelkulter method. I had never heard of it. As I am reading about it and it completely makes sense. Wood will take time to break down, allowing time for young roots to solidify at a raises position. More importanlt this apprach is long term solution and I can start small. Based on advise in this forum,

I have been already experimenting with mound planting since last one year and those plants so far have done well but I am concerned about this location since deluge will be a lot and these two shrubs roots will want to go deeper.

I will post few photos later today. Fortunately concerned area is not too big.

A handy device for handling storm water is a water level. It's more accurate than economy priced transits and economy transits aren't cheap. Sounds like your main problem is inconsiderate neighbor diverting storm water into your yard instead of to public storm drains in street and alley. In case you aren't aware,home foundations on soil with high clay content suffer damage from sudden flooding of surrounding surface.

The neighboring house (source of water) is at a higher elevation. Our house is at the bottom of the totem pole. Many of our neighbors are affected.I am told there has been a sudden rise of water table in the last 6-7 years.

But here are the images. (Excuse the weeds .). Mock orange planted in June and now the mound has reduced by 4 inches or so.

Here below you can see the fence in background the source of water from neighbor. Mock orange is at center right and Weigela is at center left and both at the end of slope. The rose of sharon far right in background planted many years ago has survived the deluge since it is at 8 inches or so elevation from the mock orange.

Some comments did not get added. Adding again.

I just feel the mounds for the two plants are not big enough for the plants to survive as the roots will go further down into the soil. Would you agree ?

I'm not qualified to predict how those plants are likely to do where they are located. After hearing how much slope is in grade I have to wounder if berm(s) and/or swal(s) could help. This being a neighborhood wide situation requires far more than photos and secondhand observations. Has the community put their heads together on this?

I should mention that neighbor behind the fence has a pump to drain water to street drain that gets turned on once a month during winter. Neighbor on left has planted water loving plants. Problem is excarbated only during rainy months december to end of march, rest of the year stays quite dry. Thanks.

Well your original plan to keep those plants feet out of water seems reasonable.

Here is a wider view. The sump on left was added few years ago, did not help much. Plants added down the slope all on lhs are all water loving plants. One experimental hosta planted last year on a mound did do well.