Rules re: building around and over a storm drain easment

[Jayro]

After waiting patiently for several years,  we spent a considerable amount of our savings in a lot in Southampton ( 77005). Despite the drawback of sitting alongside the busy Greenbriar, we invested in it specifically for its corner location and size.  None if the several surveys done before closing noted any utility easements. Seller denies any knowledge. However we were tipped off by a kind neighbour who was surprised that we were planning a completely new build.
An exhaustive and convoluted search confirms the presence of a storm drain easement running right through our property making our home  plans ( designed over a year) useless. We’ve lost a ton of time and money. Not mention a lot of heart that went into all of this. 
While we are gathering steam and looking at possible legal courses, we are also trying to determine what building area we can salvage. It ends up being a weird trapezoid that will take a very creative architect to pull off a design that meets our needs.  More $$.....unfortunately. 
Questions:

1. How close to the easement can we build?  
2. Can we cantilever a portion of our second floor over the easement?  It would be 12 feet above at least. 
3. We are assuming the easement width will be around 16 feet ( we are told by the plat map that its a 10’ diam pipe and we left another 3 ft e on each side).  Is this correct?
The easement specs and rules around it have been ridiculously difficult to pin down.

note: An interesting and puzzling observation.  From city of Houston, Open Records - we found copies of previous applications to build on the easement. These were approved!  Does this mean we dont need to consider the easement? 

We have called and written to every city office imaginable and spent countless hours pacing the internet.   We hope this forum with so many knowledgeable experts will give us some direction. 
many thanks in advance. 
Jay
 

[Specwriter]

Jayro, you have spent considerable time, anguish, and money so far. Get an attorney who specializes in these matters (the local bar association can provide a list) and determine if the previously approved applications are still valid or if they are a basis for a new application to build in the easement. Good luck.