Seaming two surfaces so they don't overlap

Sailing unfamiliar waters a bit working on a survey for an area that has flooded many times in the past. One of these developments that was done with little to no drainage plan. The entire neighborhood is a flooding disaster badly impacting a dozen or so homes. A large area, maybe 60 plus acres to the north of the neighborhood was cleared at some point and all of the meltwater in spring is channeled directly into this neighborhood, where residents have done just about everything conceivable to make the problem worse. The ditches and culverts are completely dysfunctional. I'm trying to provide the engineer with a comprehensive picture of what's going on so he can begin to design a solution.

I've done topo all through the immediate area and I also have a .shp file of contours that cover the wider area derived from Lidar data flown in 2019. What I'm trying to figure out is how to seam the two surfaces together so they don't overlap. The surface that I created in Carlson Survey running on 2023 Map3D is shrink wrapped and has the fine detail needed. I'm trying to come up with a way so that the lidar surface covering the larger area and my surface don't overlap, create a seam between my shrink wrapped surface boundary and the wider Lidar surface coverage. 

I know there must be a way to accomplish this, I just don't know what it is or how best to go about it. Hoping someone out there can get me pointed in the right direction.

Cheers all. TIA