A local civil engineer
should be able to help. Often times surveyors have a Professional Engineer on staff that does this type of work. I am licensed as a PE, but not in your state. The trouble is, when you start to get into engineered solutions, the cost goes up quickly. At a minimum, they will want to do get a drill rig out there and drill some test holes.
I can recommend the "Land Development Handbook" published by the Dewsberry Companies as a good general resource. Again,....expensive.
Additionally, the US Army Corps of Engineers (USACE) has several engineer manuals available for free download. They are pretty dry reading, but may be helpful if you have some familiarity with soil engineering and want to try to crunch numbers yourself. I have their "Slope Stability" manual and I see "Retaining and Flood Walls" and "General Design and Construction Considerations For Earth and Rock-Fill Dams" that might also be useful.
In a more general sense, for earthwork structures on a slope, it is best to cut into the slope and create a level spot so your structure is "keyed in". You want the weight of your berm/dam/whatever and all of the
water behind it to be fully supported by a flat stable surface.