17.3 Environmental Flow Assessment and Water Resources…
399
17.3.5.5 Cumulative Effects of Development
Two scenarios were modeled to demonstrate the cumulative effects of development
on flows downstream. These scenarios both contemplate an additional (hypothetical)
reservoir being constructed in the Yong’an catchment upstream of the point where
Zhu Creek meets Yong’an Creek. The modeling assumes identical levels of local
demand as those from Zhuxi Reservoir but, significantly, does not involve the transfer
of water out of the catchment (i.e., it is assumed this reservoir only supplies relatively
small local demands).
Scenario 6 is based on the proposed 2020 arrangements. As such, the results for
this scenario should be compared to those for the current planned development (S2).
Scenario 10 is based on the 2020 arrangements with modified Changtan Reservoir
operating rules and the provision of environmental flows. The model results for this
scenario should be compared to the results from Scenario 5. This second scenario
represents the most extreme variation from the arrangements proposed in the Taizhou
comprehensive plan considered and modeled as part of the pilot study.
As the new hypothetical reservoir is not connected to the Zhu Creek and the
Yongning systems, there are no implications for supply from the Zhuxi or Changtan
Reservoirs, nor for flows within Zhu Creek. Therefore, the comparison of modeling
results only needs to focus on flows in Yong’an Creek, Ling River, and Jiao River.
Figure 17.9 shows the impact of the additional reservoir on mean annual flows.
While the impact is relatively small, it would be greater if the additional reservoir
were used to supplement supplies in other parts of Taizhou as well as serve local
demands.
The key question is at which point these cumulative effects have an unacceptable
impact on the environment, which needs to be considered in the context of the
specific environmental flow objectives of the river. The environmental assessment
undertaken does not allow for a definitive recommendation on the threshold at which
these impacts will mean an unacceptable level of ecological risk. The most important
element to recognize is that there is a point at which development will impact the
environment, and, even where that threshold is unknown, resource managers should
be aware of the risk, monitor trends within the relevant indicators for the flow, and—if
possible—set flow objectives which must be achieved.
17.3.5.6 Effects of not Proceeding with Planned Developments
The first (S7) assumed Zhuxi Reservoir was not in fact built by 2010. The model
results indicate that the predicted 2010 demands could generally be met by existing
infrastructure, subject to the irrigation demands from Changtan Reservoir being
reduced to the 2020 demand levels.
All users on Zhu Creek would receive 100% of their demands in 2010, despite
there being no reservoir to supplement their supplies. Urban/industrial users from
399
17.3.5.5 Cumulative Effects of Development
Two scenarios were modeled to demonstrate the cumulative effects of development
on flows downstream. These scenarios both contemplate an additional (hypothetical)
reservoir being constructed in the Yong’an catchment upstream of the point where
Zhu Creek meets Yong’an Creek. The modeling assumes identical levels of local
demand as those from Zhuxi Reservoir but, significantly, does not involve the transfer
of water out of the catchment (i.e., it is assumed this reservoir only supplies relatively
small local demands).
Scenario 6 is based on the proposed 2020 arrangements. As such, the results for
this scenario should be compared to those for the current planned development (S2).
Scenario 10 is based on the 2020 arrangements with modified Changtan Reservoir
operating rules and the provision of environmental flows. The model results for this
scenario should be compared to the results from Scenario 5. This second scenario
represents the most extreme variation from the arrangements proposed in the Taizhou
comprehensive plan considered and modeled as part of the pilot study.
As the new hypothetical reservoir is not connected to the Zhu Creek and the
Yongning systems, there are no implications for supply from the Zhuxi or Changtan
Reservoirs, nor for flows within Zhu Creek. Therefore, the comparison of modeling
results only needs to focus on flows in Yong’an Creek, Ling River, and Jiao River.
Figure 17.9 shows the impact of the additional reservoir on mean annual flows.
While the impact is relatively small, it would be greater if the additional reservoir
were used to supplement supplies in other parts of Taizhou as well as serve local
demands.
The key question is at which point these cumulative effects have an unacceptable
impact on the environment, which needs to be considered in the context of the
specific environmental flow objectives of the river. The environmental assessment
undertaken does not allow for a definitive recommendation on the threshold at which
these impacts will mean an unacceptable level of ecological risk. The most important
element to recognize is that there is a point at which development will impact the
environment, and, even where that threshold is unknown, resource managers should
be aware of the risk, monitor trends within the relevant indicators for the flow, and—if
possible—set flow objectives which must be achieved.
17.3.5.6 Effects of not Proceeding with Planned Developments
The first (S7) assumed Zhuxi Reservoir was not in fact built by 2010. The model
results indicate that the predicted 2010 demands could generally be met by existing
infrastructure, subject to the irrigation demands from Changtan Reservoir being
reduced to the 2020 demand levels.
All users on Zhu Creek would receive 100% of their demands in 2010, despite
there being no reservoir to supplement their supplies. Urban/industrial users from