Arcuate, lightweight composite panels, which are transportable on flatbed trucks, are interconnected onsite for forming a temporary fluid tank. A shaped groove along one end of the panel and a shaped tongue along an opposing end of the panel permit a panel to be lifted vertically above and offset another of the panels and then slid axially together, with the tongue of one panel engaged in the groove of the adjacent panel. If the ground on which the tank is to be assembled is uneven, the panels can be misaligned vertically along the interconnected tongue and groove to accommodate the unevenness of the ground. Where the tank does not engage the ground about the entire bottom edge, a liner can be placed inside the tank and connected to the tank using a hook and loop fastening system.