Monitoring of the Iron Gate Hydropower and Navigation System on the Danube River - page 2

Reservoirs

2 reservoirs of the Iron Gate HPNS (Fig 4) have different characteristics. The reservoir upstream of the IG1 dam has 3.500 million m3 volume under average hydrologic conditions; this was an increase of about 2 100 million m3 compared to the volume of the Danube's natural channel.

Major characteristic of the IG1 reservoir is variable length, backwater magnitude, and volume, which are a function of discharge and the hydro-power plant's operating mode. At low flows the backwater stretches along a length of the Danube of about 310 km (up to km 1.255), along about 100 km of the Sava, and along about 60 km of the Tisza River.

The downstream IG2 reservoir is considerably smaller (only 80 km long) and does not extend beyond the channel of the Danube.

 

Operation regime of IG1 HPP

Contrary to other reservoirs, where the operating mode is generally established at the dam, the reference cross-section for the definition of the water level regime in the IG1 reservoir is at the mouth of the Nera River (km 1.075 of the Danube), some 132 km upstream from the dam (Fig. 5). This profile was selected because of its location at the upstream end of the Danube stretch shared by Serbia and Romania, and also because of specific characteristics of the riverine terrain.

The operating mode of the hydro-power plant was determined bilaterally, via several agreements between the two countries. The first such agreement between the SFR of Yugoslavia and the SR of Romania (1963) established a 68/63 operating mode. Operation of the IG1 HPP began in 1972 in the 68/63 operating mode, but already in 1974, bilateral negotiations began with respect to increasing water levels, first on an experimental, and then a permanent basis. Namely, the IG1 main structure was designed and built to allow for an increase in the reservoir's water level to a higher backwater regime, which would result in a significantly higher power generation efficiency. Following the successful conclusion of negotiations, a new agreement was signed in 1977; this Agreement defined the construction of an additional riparian land protection system and the permanent operation of the IG1 HPP in the 69.5/63 mode.

As monitoring, measurement, and analyses were conducted during the course of operation in the 69.5/63 mode, the idea was conceived to operate the system at even higher backwater elevations. The decision was made to keep the existing extreme levels (69.5 and 63 m above sea level), but to considerably increase the duration of higher backwater elevations, when feasible.

Since these conditions were expected to yield some negative effects, the impact of the new operating mode (referred to as the 69.5+ operating mode at the mouth of the Nera) on riparian lands was analyzed. The signing of the new agreement in 1987 marked the beginning of experimental operation of the IG1 HPP with water levels of the Danube at elevations higher than 69.5 m above sea level at the mouth of the Nera (hereinafter referred to as the 69.5+ mode). The obligations of the contracting authorities with respect to the present, permanent 69.5+ backwater regime were defined in the 1998 Convention on Operation and Maintenance of the Iron Gate 1 and Iron Gate 2 HPNS.

All IG1 HPP operating modes were defined by water level elevations for characteristic discharges, or discharge curves over a low flow to an extremely high flow range at control cross-sections near the mouth of the Nera (km 1075) and at the dam (km 943+000).

The 69.5/63 mode („a" in Fig. 5): The hydro-power plant operated in this mode from 1972 to 1976. When discharges of the Danube were less than 7350 m3/s, the headwater levels at the dam had to be maintained such that the water level at the mouth of the Nera remained at 69.00 m above sea level; at higher discharges, the headwater level at the dam was maintained at 63.00 m above sea level and the water level at the mouth of the Nera established its natural water level regime.

The 69.6/63 mode („b" in Fig. 5): The hydro-power plant operated in this mode from 1977 to 1985. When discharges of the Danube were less than 9,750 m3/s, the headwater levels at the dam were maintained such that the water level at the mouth of the Nera remained at 69.50 m above sea level; at higher discharges, the headwater level at the dam was maintained at 63.00 m above sea level and the water level at the mouth of the Nera established its natural water level regime.

The 69.5+ mode („c" in Fig. 5)1: Operation in this mode began in 1985. Headwater levels at the dam were maintained such that design water levels were established at the mouth of the Nera. This operating mode was precisely defined in the 1998 Convention.

In the immediate zone of the reservoir, between the IG1 Dam and rkm 1025, the highest water levels occur at low discharges of the Danube. Upstream of the mouth of the Nera River, water levels of low and average flows are permanently increased, while flood levels are similar to natural conditions. Water level changes at characteristic cross-sections along the reservoir (Banatska Palanka at rkm 1076.65 and Zemun at rkm 1073) are shown on Fig. 6.


 

1 Regime 69.5+ is also known as “up to 70.3 at the mouth of the Nera River”


 

 

Fig4
Fig. 4:  Schematic representation of Iron Gate HPNS location on the Danube River

 

Fig5
Fig. 5:  Discharge rating curves for different IG1 HPP regimes

 

Fig6
Fig. 6:  Discharge rating curves for characteristic cross-sections of the IG1 reservoir