Transcript IWA Poster Template

An Analysis of the Pollutant Loads and
Hydrological Condition for Water Quality
Improvement for the Weihe River
Introduction
For implementing water resources management in the Weihe River basin, water resources assessment is firstly necessary and important. The accuracy of
water resources assessment relies on predictability of the hydrological cycle. Different land use, topography, geology and soil conditions, and artificial water
uses (mainly agricultural irrigation) determine the complexity of hydrological characteristics in this basin. This research attempts to incorporate all available
spatial information into the hydrological modeling by a distributed approach.
Results & Discussion
Weihe River Basin
Before 1993 the annual total flow had been around 3,000 million cubic
meters per year (MCM/yr), while after 1994 it dropped to less than 1,000
MCM/yr. Within each year, the daily flow rate fluctuates widely. Taking the
2001 record as example (Figure 3), most of the runoff was concentrated in
a period from September to October and there was apparently a dry
period from March to July with very low daily flow. A hydrological analysis
was conducted regarding the annual variation of the daily flow in 2001.
The maximum, minimum, and mean (corresponding to a probability of
50%) daily flow rates are 501, 1.8 and 14.6 m3/s, respectively, showing a
very uneven distribution. If the low flow rate corresponding to a probability
of 75% is considered, it is only 6.41 m3/s.
4000
Flow(MCM/yr)
3000
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Flow Rate(m 3/s)
Weihe River is the biggest tributary of the Yellow River - the second
longest river in China. Figure 1 shows the map of the Weihe River basin
and its location. With a total length over 810 km, the Weihe River covers a
basin area of 134,000 km2. The middle and lower basin area is called the
Guanzhong Basin, one of the richest agricultural areas in China from the
ancient time where the famous ancient capital city Xi’an is located.
Nowadays with the fast urbanization of this area, population has increased
quickly, and human activities have greatly influenced the water
environment.
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1990 1991 1992 1993 1994 1995 1996 1997 1998 1999 2000 2001 2002
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Fig. 3 Variation of Annual Flow of Weihe River from 1990 to 2002
Fig. 1 Location Map of the Weihe River Basin
Water Quality of Weihe River
Figure 2 summarizes the results of water quality monitoring records of
2001 and 2002 along the main river channel. The dashed line in the figure
indicates the guideline values of CODMn and NH3-N for surface water
which is considered to be tolerable with its quality as a public water body.
Regarding CODMn, except for the first 4 locations in the upper rural area,
the annual average values are much higher than the tolerable level (15
mg/L), showing serious contamination by organic pollutants especially in
the most densely populated area (location number 7 and 8). Regarding
NH3-N, even in the upper rural area, the annual average values (location
number 2 and 3) are 4 to 8 times the tolerable level (2.0 mg/L), indicating
an intensive source of agricultural pollution in that area.
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2002
CODMn(mg/L)
NH3-N(mg/L)
2001
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2001
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15.0mg/L
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2002
2.0mg/L
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Fig. 2 Water Quality Monitoring Results of CODMn and NH3-N at 13
Locations Along the Weihe River (Annual averages of 2001 and 2002)
Variation of Annual Flow of Weihe River
The total annual load of CODMn is estimated as about 1.57 x 108 kg, and
that of NH3-N as 3.7 x 107 kg. In addition to the high pollutant loads, the
river is suffering from a decline of its annual flow as is shown in Figure 3.
The maximum capacity of the Weihe River to receive pollutants but
without causing a water quality lower than the tolerable level was
estimated. The ability of the river water to dilute the incoming pollutants
and its capability to perform self-purification were taken into account. If the
low flow rate of 2001 is used for water quality control, the estimated
capacities of the river to receive CODMn and NH3-N are 4.1 x 104 and 5.5 x
103 kg/day, respectively, which are only about 14% and 8% of the present
loads. This means that a further decrease of 86% of CODMn and 92% of
NH3-N loading would have to be considered. However, it is almost
impossible to fulfil such a task from both the economic and technical
standpoints, because some of the non-point sources, such as those from
agricultural activities, would be very difficult to control. Even if all the
possible measures were taken to reduce the pollutant loads from all the
point sources to the attainable extent, the river water quality could only be
improved to the tolerable level in accordance with the mean daily flow
rate, i.e. a guarantee of water quality for merely half of the time within one
year.
The sudden decrease of the annual total flow from 1994 was partially
caused by the accomplishment of a large scale irrigation system in the
upper stream agricultural area, where an amount of 400 to 600 MCM/yr
water has been regularly diverted from the river channel. The diverted
amount is even larger in the dry years as the demand of irrigation water
becomes bigger. This results in a great decrease of the total annual flow
to the downstream, and also a much greater decrease in the low daily flow
rate and, because the rate of water withdrawal from the river channel is
often greater in the dry season. Hydrological analysis result shows that if
measures can be taken to regulate the manner of water diverting and
especially to restrict water withdrawal in the low water season, the uneven
daily flow rate distribution as shown in Figure 3 can be much improved.
The mean daily flow rate can be doubled and the low daily flow rate can
be increased by 3 to 4 times. With a larger base flow in the river channel
to increase its ability to dilute the pollutants, the task of pollutant load
reduction, as discussed above, can be much lessened.
Conclusions
Constructing a system on efficient water utilization is an urgent need in this region. Furthermore, to apply this integrated model for water resources
assessment and management in reference to the land use change and/or climate variation. The available water in 2050, which is set drought season, is
estimated about 39 billion tons. This value is less than the water demand in the Weihe basin, so it is urgent need to introduce saving-water systems in this
region.