386
17 Environmental Flow Definition and Management: A Case Study …
low baseflow (October–March), high baseflow (April–September), and the frequency
of bankfull floods. The potential environmental changes likely to be associated with
these hydrological changes include upstream migration of salt wedge, increased
sediment influx from the Yangtze River, increased salinity within near-shore environments, reduced depths in the river-channel due to sedimentation, and altered
biogeochemical cycling.
For each of the hydrological change indices, a list was made of the environmental
assets that were potentially at risk of impairment from such a change. The assets were
rated according to three conservation status classes, with the consequence of change
increasing for higher conservation levels. The degree of change was ranked into four
classes on the basis of the likelihood of impairment due to hydrological change.
The product of the consequence and likelihood gives risk of impairment, which was
grouped into five classes, ranging from insignificant to very high. Consequence and
likelihood scores were assigned to each environmental asset, and risk scores were
calculated for each asset for three future planning and development scenarios for
Reaches 5 and 6. These scenarios were developed as part of the water resources
allocation planning component of the pilot study.
17.3.3 Development of Water Resource Management Model
An integrated water quantity and quality model (IQQM) was developed to analyze
environmental flow provision and water resources allocation in the Jiaojiang River
Basin. The developed model focussed on the following:
• daily and annual reliabilities (for fixed supply volumes) for urban/industrial users
and for irrigation from both Zhuxi and Changtan Reservoirs;
• average annual supply for urban/industrial users and irrigation, both as a volume
and a proportion of the sectors’ demand, from both the Zhuxi and Changtan
Reservoirs;
• average annual transfer of water from Zhuxi to Changtan Reservoir, both as a
volume and a proportion of the maximum possible through the pipeline;
• flow data for the reaches, which was used to assess compliance with desired
environmental flows (Fig. 17.6).
In the model, the basic parameters for the planned Zhuxi Reservoir are that full
storage volume is 118.38 million m
3 and inactive storage volume is 5.14 million m
3 .
The operation rules of Zhuxi Reservoir are defined by the following factors: (1)
The Zhuxi Reservoir has multiple objectives, including water supply, flood control,
irrigation, and power generation; (2) the reservoir must firstly meet the water use
needs of Zhu Creek and then, if possible, transfer water to Changtan Reservoir.
However, the water supply operation is subject to flood-control operation, and reservoir water levels at which different uses become inactive must be defined: for irrigation: 122 m—storage volume of 34.82 million m
3 , for power generation: 120 m—a
17 Environmental Flow Definition and Management: A Case Study …
low baseflow (October–March), high baseflow (April–September), and the frequency
of bankfull floods. The potential environmental changes likely to be associated with
these hydrological changes include upstream migration of salt wedge, increased
sediment influx from the Yangtze River, increased salinity within near-shore environments, reduced depths in the river-channel due to sedimentation, and altered
biogeochemical cycling.
For each of the hydrological change indices, a list was made of the environmental
assets that were potentially at risk of impairment from such a change. The assets were
rated according to three conservation status classes, with the consequence of change
increasing for higher conservation levels. The degree of change was ranked into four
classes on the basis of the likelihood of impairment due to hydrological change.
The product of the consequence and likelihood gives risk of impairment, which was
grouped into five classes, ranging from insignificant to very high. Consequence and
likelihood scores were assigned to each environmental asset, and risk scores were
calculated for each asset for three future planning and development scenarios for
Reaches 5 and 6. These scenarios were developed as part of the water resources
allocation planning component of the pilot study.
17.3.3 Development of Water Resource Management Model
An integrated water quantity and quality model (IQQM) was developed to analyze
environmental flow provision and water resources allocation in the Jiaojiang River
Basin. The developed model focussed on the following:
• daily and annual reliabilities (for fixed supply volumes) for urban/industrial users
and for irrigation from both Zhuxi and Changtan Reservoirs;
• average annual supply for urban/industrial users and irrigation, both as a volume
and a proportion of the sectors’ demand, from both the Zhuxi and Changtan
Reservoirs;
• average annual transfer of water from Zhuxi to Changtan Reservoir, both as a
volume and a proportion of the maximum possible through the pipeline;
• flow data for the reaches, which was used to assess compliance with desired
environmental flows (Fig. 17.6).
In the model, the basic parameters for the planned Zhuxi Reservoir are that full
storage volume is 118.38 million m
3 and inactive storage volume is 5.14 million m
3 .
The operation rules of Zhuxi Reservoir are defined by the following factors: (1)
The Zhuxi Reservoir has multiple objectives, including water supply, flood control,
irrigation, and power generation; (2) the reservoir must firstly meet the water use
needs of Zhu Creek and then, if possible, transfer water to Changtan Reservoir.
However, the water supply operation is subject to flood-control operation, and reservoir water levels at which different uses become inactive must be defined: for irrigation: 122 m—storage volume of 34.82 million m
3 , for power generation: 120 m—a