Hume and Dartmouth Dams Operations Review Design and Operation of Hume DamHume Dam consists of four embankments and a concrete spillway section. The main earthen embankment (embankment number 1) is on the southern (Victorian) side of the concrete spillway section. A much shorter earthen embankment (embankment number 4) is on the northern side of the concrete spillway section. Embankment number 2 is an earthen embankment in a saddle to the south of Embankment number 1. Embankment number 3 is a low earthen embankment south of embankment number 2, near the Latchford Army barracks. The total length of Hume Dam (including earth embankments on both sides) is 1 616 m. The height of the spillway hoist bridge above the bed of the storage is 51 metres. The total quantity of concrete and earthwork in the dam is 440 000 and 3 300 000 cubic metres respectively. The capacity of the Hume Reservoir is 3 038 gigalitres at a full supply level of 192 m relative to the Australian Height Datum. The total surface area when full is 201.9 square kilometres. The surface area is important both for the available space for recreational use, and the amount of evaporation. The main earthen embankments (embankment number 1 and 4) have a central concrete core wall. This core wall is 1.8 metres thick at its base and 0.6 metres thick at the crest. On both sides of the core wall there is a narrow zone of selected clay plus a vertical drainage zone on the downstream side. The core wall is not intended to provide major structural support, this is provided by the earth, the core wall acts as an impervious layer, providing the "water proof" component of the wall. The enlargement of the capacity of Hume Dam completed in 1961 comprised the addition of 29 spillway gates.
There are four main modes of operation of Hume Dam:
An overview of some key operating constraints and the above modes of operation is given below. Special cases where the rules of operation may be temporarily waived are also briefly discussed.
Operating constraintsVariations in release rates are frequently required during the various modes of operation of Hume Reservoir in response to changing downstream requirements. Operating constraints include: - Rates of fall; - Maximum flow rates; and - Minimum flow rates. Limits to the rates of fall of the River Murray downstream of Hume Dam (at Heywoods gauge) and downstream of the Kiewa River Junction (at Doctors Point) have been adopted to provide adequate warning of river level changes, and to minimise riverbank slumping. These maximum rates of fall are 0.2 metres per day at Heywoods gauge (located several hundred metres downstream of Hume Dam) and 0.15 metres per day at Doctors Point (located just upstream of Albury). The maximum flow rate (except during pre-release or spilling modes of operation) corresponds to a lower limit of river channel capacity between Hume Dam and Lake Mulwala. This maximum flow rate is 25 000 megalitres per day. Minimum releases are made to ensure that there is some water in the river for environmental, and small scale consumptive demands. The minimum releases are 600 megalitres per day immediately downstream of Hume Dam (at Heywoods gauge) and 1 200 megalitres per day upstream of Albury (at Doctors Point).
Filling modeDuring the filling mode, minimum releases are maintained when water requirements can be met from downstream tributaries. Minimum releases are maintained to enable the reservoir to refill typically during winter and spring. However, high inflows at other times of the year may sometimes lead to increases in storage.
Pre-release modeA 'pre-release' is a release at a rate higher than downstream requirements. Pre-release only occurs when the storage level and inflows are sufficiently high that taking into account the current conditions, and expected demands, the storage will just fill under lowest (?) on record inflows. The period of record used to determine this is in excess of 100 years. This topic is covered in more detail on the PRE-RELEASE PAGE (to be included). Pre-releases are made at rates up to channel capacity at Albury (25 000 ML/day) but can be higher with the agreement of affected landholders.
Spilling modeWhen the reservoir is full or near full, the spillway gates at the Dam are used, in conjunction with the power station and irrigation outlet valves, to pass inflows. The aim of flood operation is to pass floods so that the magnitude of the flood downstream is no greater than would have occurred without the Dam in place. If sufficient airspace is available prior to the arrival of a flood, significant flood mitigation is possible. Overall, Hume Reservoir provides a large degree of flood protection downstream.
Release ModeReleases are made from the storage (at rates no greater than river's channel capacity) to meet downstream water requirements. The release requirement is determined from all downstream water uses, estimated river transmission losses, with adjustments for contributions from all tributaries and storages downstream. Downstream requirements are reviewed on a daily basis, and releases are varied in response to the changing demand in order to conserve resources in the storage. Transfer of water to Lake Victoria is sometimes required early in the irrigation season in order to overcome channel capacity constraints in the mid Murray (particularly around Barmah) which may arise later in the season. Such transfers assist in meeting water requirements in the lower Murray. This is usually required when there is little or no Commission water available in Menindee Lakes, and tributary flows downstream of Hume are low for an extended period.
Special circumstancesIf there are special circumstances, operating rules associated with the above operating modes may need to be temporarily suspended in the short or medium term. Special circumstances may arise from time to time due to:
After consideration by the Commission or Commission office, the special circumstances may impose operational constraints for certain periods of time on the following:
Operation with Dartmouth DamHume Reservoir is used as the primary storage for the River Murray while Dartmouth is primarily used as a drought reserve. The two storages are operated in harmony with the maximum storage level in Dartmouth Dam being related to the time of year and the volume stored in Hume Reservoir. Refer to the Review of the operation of Hume and Dartmouth Dams. |
RIVER MURRAY WATER
