Issue with Bounds: Unbounded solution. PLEASE HELP!!!

[AB]

Hello All,

I am trying to maximize my objective function which is equation E4. When i place the lower bound on h, GAMS returns : ** Unbounded solution. A variable has reached 'Infinity'. Largest legal value (Rtmaxv) is 1.00E+10

In this program, I am trying to find the value of x which will maximize the value of Q. In the code i have below, i have placed bounds on Q, x and h. The issue I am having is that GAMS simply uses the upper bound I have given the problem as the maximum value. In this case, Q. Now this makes sense because before when the problem was unbounded a variable could go to 1.00E+10, but I don't understand why my system of equations is doing that in the first place. Does this make sense?? I have spent alot of time on this and cannot figure out what the issue is. ANY input would be most appreciated. 

Thank You!!!

Also, one more thing, values of x do not change with changes in values of Q, which is the heart of the model. That is what I am trying to solve for. That is, x =416.66 regardless of the value of Q. Q=200, 300, 800, x will always equal 416.66. I dont understand what the issue is. If anyone could please help me understand anything further about this issue I would be most grateful!! 

scalars

           d mean ocean SWE                     /14/

           s saltfreshwater ratio                    /1.025/

           xw well distance from coast line    /1000/

           y distance between wells              /0/             

           phi_1 freshwater potential             /2.5/;

parameters          

         C1 coefficient                                /0.006/

         C2 coefficient                                /0.00079577/;

positive variable   

                          h     Freshwater head

                          Q     Optimal pumping rate

                          x     saltwater toe length  ;

free variable       Z  objective variable;

equations

E1 constraint on well pumping equation

E2 Equation for the Freshwater potential

E3 toe constraint

E4 objective fcn for max pumpage;

E1..  phi_1=e=0.5*(h**2-s*d**2);

E2..  C1*x+(Q*C2*log((Power((x-xw),2))+(y**2))/((Power((x+xw),2))+(y**2)))=e=phi_1;

E3..  x=l=xw;

E4..  Z=e=Q;

E5..  h=g=1;

Q.up=600;

Q.lo=200;

x.lo=1.0e-3;

h.lo=1;

model saltwater /all/;

solve saltwater using NLP maximize Z;

* I dont know what execerror does

execerror=0;

display Q.l, x.l, Z.l, h.l;