The negative buoyant flow into and through a regulating pond is analysed by numerical scheme. The controlling parameter of density current in the pond is found to be the inflow densimetric Froude number, $Fr_e$. Two vortices are formed and notable at the right corner and above the sunken flow in th pond. For given inflow characteristics, the required outflow temperature, the combination of dimensions of the pond and the residence time of the inflow in the pond are determined.