Demonstrations are initiated using a gravel-filled tank, which incorporates facilities for supplying water to the surface of the gravel and measuring the runoff. The gravel tank is manufactured in stove enamelled mild steel supported by a painted mild steel frame. The equipment can be bench mounted or free standing on a laboratory floor. Water is supplied to two overhead square pattern spray nozzles via a flow control valve, flow meter and solenoid valve. Detachable see-through curtains around the tank contain any spray. Runoff is conducted to an outlet at one end of the tank. A collection and measuring unit is located near to the outlet from the tank. This comprises a traversing vessel divided internally into 17 storage compartments.
The collecting vessel is mounted on a plinth incorporating a motor drive and central drainage trough. A control console is used to control the traversing vessel and the water supplied to the spray heads. The time each compartment is located under the tank outlet can be preselected and the overall time from the start is displayed. Water collected in the vessel provides an immediate histogram of runoff as a function of time. A range of accessories allows demonstrations of surface reservoir retention, depression storage effect and land drainage. These comprise: Polythene sheet for impermeable catchment Four plastic containers for reservoir storage Permeable pipe for tile drain