Removable barrier for protecting tunnels and other structures from flooding and other hazards

A removable barrier apparatus for preventing fluid from entering a walled structure, the barrier apparatus configured for operably attaching and anchoring to the walled structure, the barrier apparatus comprising:

• a fluid retention member including an opening, a pneumatic collar, and a pliable membrane extending beyond the opening and the pneumatic collar, wherein the pliable membrane is configured to take a shape of an interior surface of the walled structure in use and further configured for intercepting a fluid entering the walled structure through the opening;
• wherein the pneumatic collar is in the form of an annular ring integral with the pliable membrane and is positioned around an interior surface of the pliable membrane and proximate the opening, the pneumatic collar configured to press and hold the pliable membrane against the interior surface of the walled structure upon installation, the barrier apparatus being configured such that, in use, the pliable membrane fills up with the fluid that enters through the opening and increasing pressure from the fluid intercepted by the fluid retention member presses the pneumatic collar and the pliable membrane against the interior surface of the walled structure, thereby creating and tightening a seal between the barrier apparatus and the walled structure;
• and
• a netting structure, the netting structure encompassing the pliable membrane, the netting structure being positioned between the pliable membrane and the interior surface of the walled structure during use and further configured for operably attaching and anchoring the fluid retention member and the netting structure to the walled structure.