A plurality of closable and removable containment berm wall supports are preferably each made from three flexible coated fabric layers and preferably each wall support incorporates three reinforcing members and incorporates a closure means that selectively can close the support into a closed triangular frame. Each berm wall support is designed to cooperate with a sleeve attached to a flexible sidewall of a containment berm unit and when the wall support is in a closed condition to hold the sidewall in an erected condition and when the wall support is in an open condition to allow the sidewall to assume a let down condition. The let down condition allows a wheeled vehicle or other object to conveniently transit over the wall for placement on a floor of the containment berm unit within the perimeter established by the sidewall.