How to determine ownership of Wetlands Area on the Texas Coast?

[Belinda Lopez]

We're in the midst of our due diligence on some land that includes Wetlands on the upper Texas Coast near Galveston, TX.  We believe part of the land has now been 'lost' to the state/public lands due to changes in the mean high tide line and vegetation lines.  The part we want is only about 5 acres in a parcel of 70+ acres.  The preliminary Title commitment excludes any land that may now be part of the Public land due to those changes but how do we determine what the true ownership is? Is this a wetlands delineation survey?  some sort of other special survey?  

We don't want to buy the land given that there is basically no Title insurance on the majority of the land but no one can tell us how to determine how much, if any of the full parcel is owned by either the current owner or the State!  Not sure how to move forward with this one - amny ideas?