基于经验模型的长江口南支上段压咸临界流量

doi:10.11821/dlxb201905008

摘要/Abstract

摘要：

河口区域盐水入侵,威胁三角洲地区城市淡水资源取用及生态环境安全,合理确定压咸临界径流流量,有助于进一步改进流域水库群的调度模式。以长江口南支为例,利用2009-2014年期间60余个潮周期氯度资料,综合分析多种盐度预测经验模型的有效性,确定了抑制咸潮入侵的临界径流流量。结果表明：① 咸潮入侵强度随径流与潮差组合而不同,长江口径流流量小于30000 m ³/s时可发生盐度超标现象,69%的盐度超标天数发生在流量小于15000 m ³/s时期,当径流量小于12000 m ³/s时盐度超标几率达65%;② 盐度与潮差之间为指数型曲线关系,潮差总体呈半月周期变化,根据潮差累积频率分布得到平均意义上“连续10 d盐度超标”临界条件对应的青龙港潮差约为2.7 m,由此推算得到临界大通流量略大于11000 m ³/s;③ 采用多种盐度预测经验模型进行计算,避免连续10 d盐度超标对应的临界径流流量区间为11000~12000 m ³/s,平均阈值取为11500 m ³/s;④ 在三峡及上游梯级水库联合运行后,2008-2015年长江入海最低径流流量有所增加,但仍低于压咸潮临界阈值,建议优化水库调度模式,控制长江入海径流最低流量在11500 m ³/s以上。

关键词: 压咸临界流量, 径流和潮差, 经验模型, 长江口

Abstract:

In the Yangtze River Estuary, saltwater intrusion threatens eco-environment and freshwater intake. The estimation of the critical discharge for saltwater intrusion control helps improve the regulatory schemes of reservoirs in the Yangtze River Basin. In this study, the upper south branch of the Yangtze River Estuary was selected as a typical area to determine the critical discharge for saltwater intrusion control using different empirical models. Measured salinity data of more than 60 tidal cycles were used to analyze the characteristics of saltwater intrusion processes, and the validity of four empirical models was tested. Results indicated that (1) the intensity of saltwater intrusion changes with different combinations of discharges and tidal ranges, and saltwater intrusion occurs when the discharge at the Datong station is less than 30000 m ³/s. Approximately 69% of saltwater intrusion days occur when the discharge is less than 15000 m ³/s. The probability of saltwater intrusion is 65% when the discharge is less than 12000 m ³/s. (2) The tidal range in the Yangtze River Estuary shows a distinct feature of a semi-monthly (15 days) periodical change, that is, the condition of "saltwater intrusion that ensues for more than 10 days" occurs with two-thirds frequency when the discharge is maintained at a certain critical value. On the basis of statistical analysis, the tidal range that corresponds to two-thirds frequency is determined to be 2.7 m at the Qinglonggang station. With the exponential relationship between salinity and tidal range, the critical discharge at Datong has been estimated to be slightly higher than 11000 m ³/s. (3) The periodical changes in tidal range can be roughly described using sinusoidal functions. By introducing the tidal range functions into empirical models for saltwater intrusion, the change process of salinity under a certain discharge can be calculated. By using three empirical models, the calculation results show that the critical discharge at Datong is between 11000 and 12000 m ³/s. Thus, 11500 m ³/s can be regarded as the critical discharge to control the duration of saltwater intrusion to less than 10 days. (4) After the operations of the Three Gorges Project and its upstream cascade reservoirs, the minimum discharge into the sea in 2008-2015 increased but remained lower than the critical discharge. Therefore, the regulatory schemes of reservoirs in the Upstream Yangtze River must be optimized to release additional water during dry season. In particular, the minimum discharge into the sea should be maintained to be higher than 11500 m ³/s.

Key words: critical discharge for saltwater intrusion, discharge and tidal range, empirical model, the Yangtze River Estuary

严鑫,孙昭华,谢翠松,夏军强. 基于经验模型的长江口南支上段压咸临界流量[J]. 地理学报, 2019, 74(5): 935-947.

YAN Xin,SUN Zhaohua,XIE Cuisong,XIA Junqiang. Estimation of critical discharge for saltwater intrusion in the upper south branch of the Yangtze River Estuary using empirical models[J]. Acta Geographica Sinica, 2019, 74(5): 935-947.

图/表 20

图1

图2

表1

表2

图3

图4

图5

图6

图7

表3

图8

图9

图10

表4

表5

长江口南支中上段盐度预测的统计模型

文献来源	关系式形式	变量含义
茅志昌^[16]	$S ~exp Δ H α Q β$	S为宝钢盐度;?H为青龙港潮差;Q为大通流量
郑晓琴^[17]	$S = f Δ H, Q = a e b Δ H + a e b Δ H (c 1 Q 3 + c 2 Q 2 + c 3 Q + c 4)$	S为青龙港盐度;?H为青龙港潮差;Q为大通流量
陈立等^[18]	$S = (4.16 × 10 - 9 Q 2 - 2.745 × Q + 4.317) × 0.02404 × e 0.009085 Δ H$	S为陈行盐度;?H为青龙港潮差;Q为大通流量
孙昭华等^[29]	$C = A exp - bQ × exp a Δ H 0 + 0.7 a × cos 2 π 14.75 × t - 3$	Q为大通流量;?H₀为徐六泾潮差;t为农历日期;C为东风西沙氯度

表5

表6

式(1)中不同潮差估算模式的参数值

站点	潮差振幅	平均潮差 $Δ H 0$ (m)	潮差振幅A(m)
青龙港	上包络线A	3.5	0.8
	平均线B	2.9	0.8
	中间线C	2.9	1.4
	上偏线D	2.9	1.1
徐六泾	上包络线A	2.8	0.7
	平均线B	2.35	0.7
	中间线C	2.35	1.15
	上偏线D	2.35	0.925

表6

图11

表7

图12

表8

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序号	数据名称	时间长度(年)	类型	数据来源
1	大通站流量	1950-2015	日均值	长江水文年鉴
2	徐六泾潮差	2009、2011-2014	日均值	长江水文年鉴
3	青龙港潮差	2005、2009、2011、2014和2017年若干月份	日均值	江苏省水文水资源勘测局、文献^[17]
4	东风西沙氯度	2009-2014	日均值	上海水务局

时段	小于某级流量的累积频率(%)
时段	< 25000 m³/s	< 15000 m³/s	< 12000 m³/s	< 10000 m³/s
1950-2002	45.71	25.71	16.9	10.06
2003-2007	55.83	24.85	14.29	2.74
2008-2015	50.33	21.59	7.73	0.1

发生时间	监测点	超标天数(d)	超标时段内大通流量均值(m³/s)	资料来源
1978年冬-1979年春	吴淞水厂	64	7256	文献[9]
1987年2-3月	陈行水库	13	8467	文献[10, 12, 19]
1999年2-3月		25	9487	文献[9,10]
2004年2月		9.8	9479	文献[23]
2006年10月		9	14300	文献[11]
2014年2月		19	10900	文献[14]
2009年11月3-12日	东风西沙	10	14030	上海水务局
2013年11月15-24日		10	12240
2013年12月3-11日		9	12500
2013年12月17-25日		9	11356
2014年1月2-10日		9	12144
2014年1月30日-2月22日		24	11138

序号	东风西沙氯度 (mg/L)	大通流量 Q_c(m³/s)	徐六泾潮差 ?H_c (m)
1	250	11000	2.05
2	250	12000	2.24
3	250	13000	2.42
4	250	15000	2.61

序号	模型	潮差估算模式	计算和实测值决定系数R²	潮差估算模式	计算和实测值决定系数R²
1	茅志昌等^[16]	青龙港B线	0.45	青龙港C线	0.51
2	郑晓琴等^[17]	青龙港B线	0.85	青龙港C线	0.88
3	陈立等^[18]	青龙港B线	0.7	青龙港C线	0.74
4	孙昭华等^[29]	徐六泾B线	0.8	徐六泾C线	0.81