, 57 ,2013 2

網走川河口域で発生する塩水遡上 に関する数値的検討

NUMERICAL STUDY ON SALINE INTRUSION

IN ABASHIRI RIVER ESTUARY

1 2 Tetsuya SHINTANI and Keisuke NAKAYAMA

1 ( ) 192-0397 1-1 2 ( ) 090-8507 165

We numerically studied saline intrusion and the related river flows in the Abashiri River Estuary that connects the Ohotsuku Sea and the Lake Abashiri in northeast Hokkaido. A three-dimensional object-oriented hydrodynamic model, Fantom3D, was used to investigate the stratified flow dynamics in this estuary. In the computation, the estuary was decomposed into 15 domain objects having different sizes to properly express the narrow and highly bending river channel. The one-way nesting technique was also used to resolve depth-scale eddies in the channel. The computed results were compared to observed data obtained in Sept 2006. The water level, velocity and salinity measured at four locations along the estuary were in reasonable agreement with the computed results. The secondary flow at a bending section and the variation of mixing type along the river were also discussed using the computed results. We showed that these computed results are qualitatively agreed well with the previous investigations.

Key Words: Saline intrusion, mixing type, secondary flow, 3D numerical simulation, nesting

１． はじめに

33km2 16m

1)

2), 3), 4)

5)

(dispersion coefficient)

6)

7), 8)

9)

10)

7) Wang et al. Snohomish River Estuary 11)

3

12)

(Fantom3D)

13) 3

２． 現地の詳細

115km

図-1(a)

7km

50m 図-1(b)

7m 1m1km

(a) 道東広域図

(b) 網走川河口域拡大図

図−１ 研究対象水域

図—２ 網走港の潮位と網走湖の水位(2006年)

14) 2006 9 16

9 図-2

20cm 50cm

３． 数値計算手法

(1) オブジェクト指向モデルFantom3D

Fantom3D(ver.2β)

オホーツク海

能取湖

網走湖

涛沸湖

サロマ湖

網走川河口域

北海道道東

網走川

500m網走湖 KP7.1

KP2.5

KP4.0KP5.0

網走港

拡大図

水位，流速，塩分の比較ポイント

混合形態の確認ポイント

二次流の確認断面

KP1.7

KP3.8

15),16) (Object-

Oriented Programming: OOP)

OOP(domain specific )

(2) 数値スキーム

ULTIMATE-QUICKEST

2 Adams-Bashforth

Theta method

MITgcm Adcroft et al.17)

partial-step

partial-step

13) 図-3

13 (Domain )Domain

Domain

(OpenMP)Domain

Domain

図−３ 計算領域のDomain分割(河道部)

domain

Domain

domain 10m 10mdz 3 6m

dz=1.0m 3mdz=0.25m

24dt=2.0

CFLdomain

5m 5m5

LES 4/3

Vitousek and Fringer19

(3) 境界条件について

10)

5km20)

KP7.1

Parent domain(dx,dy=10m)

Child domain(dx,dy=5m)

KP1.7KP2.5KP3.8

KP4.0

KP5.0

KP7.1

(Domain)

４． 結果の比較と検証

図-1(b)

2.5km (KP2.5), 4.0km (KP4.0), 5.0km (KP5.0), 7.1km (KP7.1)

図-4

図-４ 水位に関する計算結果と観測結果の比較

図-5,6

図-7

図-５ 東西方向流速に関する計算結果と観測結果の比較

図-６ 南北方向流速に関する計算結果と観測結果の比較

図-７ 塩分濃度に関する計算結果と観測結果の比較

５． 数値計算結果による現象把握

10)

14) 10)

180

-1図-1

図-8(a)

cm/s

図-8(b)

(a) 干潮時の二次流分布

(b) 密度成層と二次流の干渉

図-８ 二次流に関する計算結果（流速及び密度分布）

図-９ 混合型の変化（9/19-9/20）

図-9 図-1 KP1.7 KP3.8

14) -5

unit : PSU

3

unit : PSU

68

10

12

14

30

30

18

18

6

6

(KP1.7) (KP3.8)

KP1.7

KP3.8

６． 結論

1)

Fantom3D

2)

3)

2

4) (1.7km)

(3.8km)

謝辞：

参考文献 1)

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（2012.9.30受付）