AWWA WQTC65708

The City of Oregon City's Mountain View Reservoir #2 is a 10.5 MG finished waterreservoir. The facility was originally constructed in 1915 as an open 4.0 MG facility.The original facility design was a rectangular, concrete, in-ground reservoir with a singleinlet/outlet (I/O) configuration at one corner of the reservoir. Operationally, the facilitywas originally designed in conjunction with a pumping station housing two pumps to filland draw on the reservoir through the common 18-inch vertical, floor elevation I/O.In 1952, the reservoir was expanded, by adding reinforced concrete walls above-grade, toits present capacity of 10.5 MG. At that time an emergency auxiliary outlet and pumpstation with separate power generation was added to the reservoir for redundancy andreliability. The auxiliary outlet was designed at elevation that only allowed access to thenewest 6.5 MG of storage. The original 4 MG was unavailable through the auxiliaryoutlet. Typical operation of the reservoir maintained water levels within three ft. range of theoverflow. Due tothe tight operational range freshwater brought into the tank during fill cycles was, at amaximum, only 14% of the total capacity. Field monitoring of the reservoir had nothistorically been conducted. However, CFD modeling of the original configuration of thereservoir showed that minimal mixing was occurring and hydraulically the reservoir wasshort-circuiting in a "last in, first out" manner.Structurally the facility did not meet current codes for seismic stability and in 2005seismic improvements were planned. During design of seismic upgrades to the reservoirit was decided to rectify water quality problems resulting from the common I/O design,primarily loss of chlorine residual within the reservoir due to minimal mixing andhydraulic short-circuiting. To address the problem the City requested solutions forseparating the common I/O to improve chlorine residual maintenance, mixing andreduction of short-circuiting and "dead zones."The I/O improvements separated the inlet and outlet by extending the existing auxiliaryoutlet to a 24-inch diameter inlet 240 ft. into the reservoir. A 90º degree elbow wasinstalled and the inlet pipe extended down the slope and to the floor of the original 1915reservoir. The new manifold was now located approximately 240 ft. from the outlet and 80ft. from the back wall. The I/O improvements were combined with the replacement of the primary and auxiliarypumping stations with a single pump station. This provided the capability to maintain theexisting common I/O intact and hydraulically convert it to function solely as the reservoiroutlet.The reconfigured fixed directional inlet manifold was designed to distribute fill wateracross the reservoir horizontally while at the same time the lower elevation mixed thewater vertically. To maximize the hydraulic momentum of the inlets, reducers wereadded to create discharge jets. The separation of the inlet and outlet provides the operational flexibility to operate thereservoir in a fill then draw mode, or in a continuous fill-draw mode. CFD modelingresults of the relocated inlet and manifold designed to promote mixing show a moremixed condition in the reservoir. Actual field testing has not yet been conducted. Includes figures.

Product Details

Edition:

Vol. - No.

Published:

11/01/2007

Number of Pages:

7

File Size:

1 file , 920 KB