The Model operation centered on a Hewlett Packard 1000 minicomputer with two HP2250 Measurement and Control processors. The system functioned as an on-line process control system, outputting control signals, storing raw data, processing data and providing real-time monitoring of model conditions during testing. Programs linked to events or processes requiring real-time response were given guaranteed priority in scheduling and execution. The Model operation, followed by data acquisition and storage, were given the highest priority. All other users shared the remaining computational resources on either a priority or time-slice basis. Peripheral devices included a 16 megabyte disc drive for system operations programs, 64 megabyte disc drive for all user programs and data, magnetic tape drive, matrix and daisy wheel printers, graphics plotter and digitizer, modem and remote terminals.
The tides were generated by a continuous flow between a large sump and the ocean headbay. The inflow was achieved using a 75 hp pump on a 14-inch valve control line. Outflow was by gravity through a 24-inch pipe with a slide gate control into a weir control section of the sump. The HP1000 minicomputer worked through the HP2250 processors controls the position of the valve and slide gate based on the programmed tidal elevation and feedback of the actual tidal elevation. This feedback was provided by the checking of three water level detectors in the ocean to guard against disturbances or instrument malfunction. Valve operation and water level detection were programmed to alert the operator of any malfunction.
Water exchanged in the ocean headbay were provided by longitudinal openings along the inflow and outflow pipes. Both the openings and the headbay itself were baffled to reduce the currents in the ocean caused by the continuous exchange of water. The average tidal range between mean lower low and mean higher high water was 0.058 feet. The average height of the water surface was controlled between 2 to 3 ten thousandths of a foot.
River Flows (not operational today)
River flows were controlled using constant head tanks. The operating principal of these devices was that a precise flow through an orifice could be controlled with a given level or head of water in a tank. Although the flows in several rivers could be represented, most testing deals with the flows in the Sacramento, Mokelumne and San Jouquin River systems. The Sacramento River was equipped with two constant head tanks and a metered flow tank for high flow conditions. One of the head tanks had a rotating plate with multiple orifices to increase the range of flows and still maintain a high level of precision. For extremely high flood conditions on the Sacramento River, the Yolo Bypass was simulated using a V-notch weir.
Delta Exports (not operational today)
Water export facilities were represented on the Model for the State of California Water Project from the Clifton Court Forebay at the south end of the Delta, the U.S. Bureau of Reclamation Central Valley Project just south of the Clifton Court Forebay and the Contra Costa Canal.
Agricultural Withdrawals and Returns (not operational today)
Agricultural withdrawals and returns during the summer irrigation periods are important to the flow patterns in the Delta. Withdrawals were simulated with small, metered pumps from twelve different locations in the Delta. Withdrawals ranged up to about 700 cfs at a location. Agricultural returns utilize head tanks feed open gravity drip systems at 24 locations. Return flows were typically 50 cfs. The locations of the withdrawals and returns within the Delta were established by an interagency technical committee during the construction and verification of the Delta portion of the Model.
Salinity (not operational today)
All salinities on the Model were created by adding commercial sodium chloride to tap water. During tests the ocean boundary was maintained at 33.0 parts per thousand (ppt). Fresher waters were skimmed off the ocean with a skimming weir and salt brine at 270 to 290 ppt was added to the sump to counteract the freshening of the boundary condition from river flows. The San Joaquin and Mokelumne Rivers under low flow conditions were simulated with salinities of 0.50 and 0.40 ppt respectively, as well as agricultural return flows which ranged from 0.30 to 0.90 ppt. The tap water drawn from both reservoirs and springs and did vary from 60 to 120 parts per million Total Dissolved Solids. These variations were monitored by the computer data acquisition system and with water samples. The mixing of saline water and analysis of test data utilized this known variation.
Tide Gates (not operational today)
Two tide gates were operated in the south Delta with the export of water. The operation of the gates was controlled by the computer on a predetermined schedule.