Journal of Geographical Sciences >
Developing a comprehensive evaluation method for Interconnected River System Network assessment: A case study in Tangxun Lake group
Author: Yang Wei (1991-), PhD, specialized in numerical simulation of water environment. E-mail: yangweivv@126.com
Received date: 2018-03-01
Accepted date: 2018-05-08
Online published: 2019-03-20
Supported by
National Key Research and Development Program, No.2017YFA0603704, No.2017YFC1502500
Copyright
The Interconnected River System Network (IRSN) plays a crucial role in water resource allocation, water ecological restoration and water quality improvement. It has become a key part of the urban lake management. An evaluation methodology system for IRSN project can provide important guidance for the selection of different water diversion schemes. However, few if any comprehensive evaluation systems have been developed to evaluate the hydrodynamics and water quality of connected lakes. This study developed a comprehensive evaluation system based on multi-indexes including aspects of water hydrodynamics, water quality and socioeconomics. A two-dimensional (2-D) mathematical hydrodynamics and water quality model was built, using NH3-N, TN and TP as water quality index. The IRSN project in Tangxun Lake group was used as a testbed here, and five water diversion schemes were simulated and evaluated. Results showed that the IRSN project can improve the water fluidity and the water quality obviously after a short time of water diversion, while the improvement rates decreased gradually as the water diversion went on. Among these five schemes, Scheme V showed the most noticeable improvement in hydrodynamics and water quality, and brought the most economic benefits. This comprehensive evaluation method can provide useful reference for the implementation of other similar IRSN projects.
YANG Wei , ZHANG Liping , ZHANG Yanjun , LI Zongli , XIAO Yi , XIA Jun . Developing a comprehensive evaluation method for Interconnected River System Network assessment: A case study in Tangxun Lake group[J]. Journal of Geographical Sciences, 2019 , 29(3) : 389 -405 . DOI: 10.1007/s11442-019-1605-2
Figure 1 Sketch of the Interconnected River System Network project of the Tangxun Lake group |
Table 1 Evaluation system of IRSN scheme |
Index categories | Indexes | Units | Implications |
---|---|---|---|
Hydrodynamic evaluation indexes | Mean flow velocity | m/s | Reflecting the water renewable capability and the self-purification ability. |
Maximum flow velocity | m/s | Representing the maximum flow velocity of the lake. | |
Stagnant water ratio | % | The proportion of the stagnant water area (the velocity less than 0.0006 m/s) to the total area. | |
Water quality evaluation indexes | Water quality improvement rate | % | Reflecting the change trend of water quality indexes in lakes. |
Concentration change index | - | Reflecting the improvement of water quality in lakes, and the larger concentration change index is, the better the water quality becomes. | |
Water quality category ratio | % | Reflecting the spatial distribution of water quality before and after water diversion. | |
Water standard exceeding ratio | % | Reflecting the exceeding standard ratio of each pollutant before and after diversion. | |
Socioeconomic indexes | Economic benefits | yuan | Reflecting the environmental benefits of water quality improvement in lakes. |
Costs | yuan | Reflecting the costs incurred in the operation of the project. | |
Net benefits | yuan | It is the difference between economic benefits and costs. The greater the net benefits, the better the water diversion effect. |
Figure 2 The underwater topographical map of the Tangxun Lake group |
Figure 3 Location of sampling sites and sewage outlets in the Tangxun Lake group |
Table 2 The calibration parameters in hydrodynamic and water quality model |
Parameter name | Value | Parameter name | Value |
---|---|---|---|
Coriolis force constant | 7.27×10-5 s-1 | Wind resistance coefficient | 0.0012 |
Horizontal diffusion coefficient | 0.5 m2/s | Vertical diffusion coefficient | 0.8 m2/s |
Horizontal eddy viscosity | 8.9 m2/s | Vertical eddy viscosity | 8.9 m2/s |
Roughness | 0.02 | NH3-N degradation coefficient | 0.05 d-1 |
TP degradation coefficient | 0.008 d-1 | TN degradation factor | 0.015 d-1 |
Figure 4 Simulated and measured values at nine stations during model calibration |
Figure 5 Simulated and measured values at nine stations during model verification |
Table 3 The IRSN schemes of the Tangxun Lake group |
Connectivity schemes | Flow discharge (m3/s) | Outlets | Water diversion routes | |
---|---|---|---|---|
From Donghu Lake | From Liangzi Lake | |||
Scheme I | 40 | 0 | Outlet 1, Outlet 2 | Route A, Route B |
Scheme II | 0 | 40 | Outlet 2 | Route C |
Scheme III | 40 | 40 | Outlet 1, Outlet 2 | Route A, Route B, Route C |
Scheme IV | 0 | 40 | Outlet 2, Outlet 3 | Route C, Route D |
Scheme V | 40 | 40 | Outlet 1, Outlet 2, Outlet 3 | Route A, Route B, Route C, Route D |
Table 4 The flow velocity and stagnant water ratio under different schemes |
Schemes | Mean flow velocity (m/s) | Maximum flow velocity (m/s) | Stagnant water ratio (%) |
---|---|---|---|
Before diversion | 0.0015 | 0.0065 | 31.4 |
Scheme I | 0.0051 | 0.483 | 29.9 |
Scheme II | 0.0056 | 0.690 | 24.8 |
Scheme III | 0.0079 | 0.666 | 23.7 |
Scheme IV | 0.0084 | 0.749 | 23.0 |
Scheme V | 0.0087 | 0.743 | 21.6 |
Figure 6 Spatial distributions of flow field under different schemes |
Figure 7 Time-variation of the water standard exceeding ratios of the Tangxun Lake under different schemes |
Table 5 Water quality of the Tangxun Lake group before and after IRSN under different schemes |
Schemes | Lakes | Water quality improvement rate (%) | Concentration change index | Water quality category ratio (%) | Water standard exceeding ratios (%) | |||||
---|---|---|---|---|---|---|---|---|---|---|
NH3-N | TN | TP | I~III | IV | V | Worse than Grade V | ||||
Before diversion | TXL | - | - | - | - | 9.18 | 23.78 | 40.38 | 26.66 | 90.82 |
SL | - | - | - | - | 0 | 1.97 | 6.93 | 91.1 | 98.03 | |
Scheme I | TXL | -1.32 | 12.54 | 10.81 | 0.078 | 8.33 | 49.97 | 23.89 | 17.8 | 91.67 |
SL | 31.21 | 38.85 | 55.97 | 0.543 | 4.57 | 62.54 | 16.4 | 16.49 | 32.89 | |
Scheme II | TXL | 16.51 | 31.42 | 30.63 | 0.305 | 46.49 | 28.69 | 13.98 | 10.84 | 53.51 |
Scheme III | TXL | 15.85 | 33.5 | 32.43 | 0.321 | 45.31 | 31.48 | 13.37 | 9.83 | 54.69 |
SL | 31.21 | 38.85 | 55.97 | 0.543 | 4.57 | 62.54 | 16.4 | 16.49 | 32.89 | |
Scheme IV | TXL | 17.17 | 31.32 | 31.53 | 0.311 | 49.41 | 25.28 | 13.51 | 11.79 | 50.59 |
HJL | 21.52 | 14.87 | 51.72 | 0.366 | 6.91 | 15.25 | 43.45 | 34.39 | 93.09 | |
QLL | 2.33 | -1.6 | -62.14 | -0.298 | 21.03 | 19.03 | 29.74 | 30.2 | 78.97 | |
YL | 27.71 | 2.13 | 36.57 | 0.264 | 0 | 33.33 | 50.6 | 16.07 | 66.67 | |
Scheme V | TXL | 16.04 | 32.65 | 31.53 | 0.313 | 47.31 | 28.66 | 12.93 | 11.1 | 52.69 |
SL | 31.21 | 38.85 | 55.97 | 0.543 | 4.57 | 62.54 | 16.4 | 16.49 | 32.89 | |
HJL | 17.63 | 22.97 | 52.47 | 0.388 | 0.04 | 23.91 | 48.32 | 27.72 | 99.96 | |
QLL | 2.37 | -0.85 | -62.03 | -0.295 | 22.52 | 19.07 | 32.03 | 26.38 | 77.48 | |
YL | 27.76 | 2.2 | 36.83 | 0.265 | 0 | 33.35 | 50.57 | 16.08 | 66.65 |
Note: TXL, SL, HJL, QLL and YL represent the Tangxun Lake, the South Lake, the Huangjia Lake, the Qingling Lake and the Yehu Lake, respectively. |
Figure 8 Spatial distributions of NH3-N concentration 20 days later after the diversion under different schemes |
Figure 9 Spatial distributions of TN concentration 20 days later after the diversion under different schemes |
Figure 10 Spatial distributions of TP concentration 20 days later after the diversion under different schemes |
Table 6 Benefits and investments under different schemes |
Schemes | Total flow discharge (m3/s) | Water pollutants (kg) | Economic benefits (×104 yuan) | Costs (×104 yuan) | Net benefits (×104 yuan) | ||
---|---|---|---|---|---|---|---|
NH3-N | TN | TP | |||||
Before diversion | - | 133821.2 | 212388.9 | 18383.1 | - | - | - |
Scheme I | 40 | 119334.1 | 174779.1 | 14984.7 | 203.33 | 117.50 | 85.83 |
Scheme II | 40 | 122782.3 | 167619.4 | 16223.4 | 193.62 | 117.50 | 76.11 |
Scheme III | 80 | 107856.8 | 144923.0 | 13418.5 | 355.11 | 235.01 | 120.11 |
Scheme IV | 40 | 119391.0 | 165971.8 | 14044.5 | 234.05 | 117.50 | 116.54 |
Scheme V | 80 | 105319.4 | 143262.0 | 11252.8 | 390.99 | 235.01 | 155.98 |
Table 7 Comprehensive evaluation results of the five schemes |
Schemes | Hydrodynamic evaluation indexes | Water quality evaluation indexes | Socio-economic index | ||||
---|---|---|---|---|---|---|---|
Mean flow velocity (m/s) | Stagnant water ratio (%) | Water quality improvement rate (%) | Concentration change index | Net benefits (million) | |||
NH3-N | TN | TP | |||||
Scheme I | 0.0051 | 29.9 | 2.85 | 12.66 | 13.57 | 0.114 | 85.83 |
Scheme II | 0.0056 | 24.8 | 10.61 | 20.19 | 19.68 | 0.196 | 76.11 |
Scheme III | 0.0079 | 23.7 | 13.88 | 26.13 | 27.46 | 0.271 | 120.11 |
Scheme IV | 0.0084 | 23.0 | 14.23 | 21.61 | 19.9 | 0.213 | 116.54 |
Scheme V | 0.0087 | 21.6 | 16.78 | 28.02 | 26.62 | 0.281 | 155.98 |
The authors have declared that no competing interests exist.
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