John - You can simulate this problem soley in EXTRAN. Simply use your
pond elevation-area data to set up a storage node on the E1 and E2
cards. Inflows from whatever source can be coded on the K1-K3 cards;
the creek and its inflows and levels can also be included in the model;
however you will have to set up boundary conditions for the creek on the
I and J cards.

Hope this helps
Ron Kilmartin
ronkilmartin@attbi.com