Evaluation of small watersheds inflowing Lake Shinji against the water environment

Shimane University Hiroaki SOMURA

SHIMANE University

International SWAT Conference in Paul Sabatier University 17-19 July 2013

Background of the study

Rapid aging of the population resulting from

the decline in the birthrate

Rough management in agriculture and forestry

Watershed degradation

Impact / damage to economic activities, water environment and biodiversity 2

Linkage of river basin activities and lake biodiversity / ecosystem

Lake

Ocean

Mountains

Human activities

About Lake Shinji: Why important?

http://fishing-forum.org/zukan/mashtml/M000712_1.htm

Gymnogobius taranetzi,1878

Size: 5cm

http://www2.odn.ne.jp/shokuzai/Shijimi.htm

Corbicula japonica Prime,1864

Size: 2cm

1. Brackish lake: Delicate balance of saline and fresh water 2. Salinity level: 1/10 of sea water 3. Average water depth: 4.5m 4. The third largest brackish lake in Japan (79.1km2) 5. 80 species of brackish water fish and shellfish 6. Annual catch of the clam is about 7,000t (40% of National total) 7. Sales amount of the clam is about 40 million dollars in the lake

2,200t (2011) 23% of NT

3,700t (2010)

Less than half?

3

Lake Shinji Lake Nakaumi

Rain

Rain & others

Shimane

Tokyo

Location of Hii River basin

Outlet

About 600 km away from TOKYO

Hii River Basin About 920km2

Forest: about 80% Paddy field: about 10%

Ino R.Yuna R.Goemon R.Shintate R.Sasafu R.Hii R.Ohono R.Aika R.Higashinagae R.Kimachi R.Sada R.Tamayu R.Inbe R.

Percentage of catchment area of rivers flowing into Lake Shinji

73.3% Hii River

Average Water Quality - Hii River and Lake Shinji -

全リン

0

0.01

0.02

0.03

0.04

0.05

0.06

0.07

0.08

1990 1992 1994 1996 1998 2000 2002

T- P (Hii R.)T- P (L.Shinji)

Concentration (mg/L)

Lake Shinji Hii River

Water quality standard

（Data: Shimane Prefecture） T-P

Made by Dr. Ikuo TAKEDA

Lake Shinji Lake Nakaumi

Rain

Rain & others

Shimane

Tokyo

Published in Journal of Hydrology Results of Previous Study -Hii River basin-

Outlet

Impact assessment of Hii River basin to downstream lake water environment

Hii River Basin About 920km2

Forest: about 80% Paddy field: about 10%

SS: 27 tons/km2

TN: 1053 kg/km2

TP: 43 kg/km2

Paddy fields

Upland fields (include Japanese tea

and persimmon) Forests Residen.

areas

SS (ton km-2) 1.9 3.1 0.5 0.6

25.4 119.6 11.6 23.6

TN (ton km-2) 828.7 5261.4 180.5 330.2

1277.9 8363.0 425.2 1107.8

TP (kg km-2) 5.3 15.3 0.7 2.3

77.6 595.7 16.9 67.5

Forests < Residen. areas < Paddy fields < Uplands

Fine day

Rainy day

Results of Previous Study Unit loads from each land use under both fine and rainy days conditions

Impact assessment of Hii River basin to downstream lake water environment

Published in Journal of Hydrology

SS，TN，TP loads，there are the biggest impact from the forests TP load, agricultural lands has big influence against total loads

Results of Previous Study Ratios of SS, TN, and TP loads from each land use against total loads

Impact assessment of Hii River basin to downstream lake water environment

SS TN TP

17%

18%63%

2%p

20%

30%48%

2%p

22%

36%

39%

3%p

Forests

Paddy fields

Upland fields

Residential areas

Published in Journal of Hydrology

Objectives

The aim of this study

Estimate the amount of flow and nutrient discharges from small river basins to the downstream lake

Evaluate influences of the basins to the lake water environment

For more accurate analysis, we have paid attention to small river basins around the lake along with Hii River basin

Prepare Data sets

Make SWAT Project

Simulate Flow

Simulate Nutrients

Scenario Analyses

Impact assessment

Toulouse

We didn’t consider small river basins around the Lake Shinji

Goal

Lake Shinji Lake Nakaumi

Rain

Rain & others

Shimane

Tokyo

Forests: 81% Paddy fields: 13% Upland fields: 2% Residential area: 2% Others: 2%

Outlet

Location of Study Area

Lake Shinji watershed About 1194 km2

Simulation periods and input data Watershed Divided into 64 subbasins Input data period: 1985-2011 Calibration: 1988-1997 (10 years) Validation: 1998-2011 (14 years) Warm-up: 1985-1987 (3 years) Target of simulation Flow: Monthly basis

DEM and Soil GIS data

10m DEM 1:200,000 Soil Data

Land use GIS data

Previous study Current study

Refinement

Parameter values calibration Parameter values were calibrated “Manually” basically

Alpha-baseflow: Baseflow Filter Program (J.G. Arnold and P.M Allen, 1999 )

Sensitive parameters Ranking Parameter Definition

1 ESCO Soil evaporation compensation coefficient

2 CANMX Maximum canopy storage

3 CN2 Moisture condition II curve number

4 Sol_AWC Available water Capacity

5 BLAI Potential maximum leaf area index for the plant

6 Sol_Z Depth from soil surface to bottom layer

7 GWQMN Threshold water level in shallow aquifer for base flow

8 Ch_K2 Effective hydraulic conductivity of channel

Model Performance Evaluation 1. Nash-Sutcliffe efficiency (NSE) 2. Coefficient of determination (R2) 3. RMSE -observations standard deviation ratio (RAR) 4. Percent bias (PBIAS)

Model performance criteria Satisfactory

Flow: NSE > 0.5; RSR ≤ 0.7; PBIAS ±25%

(Moriasi et al., 2007)

Reproducibility of steam flow Calibration 1988-1997

Validation 1998-2011

NSE 0.64 0.51

R2 0.75 0.65

RSR 0.60 0.70

PBIAS 15 18

0

20

40

60

80

100

120

140

160

180

Dis

char

ge c

ms

Otsu_Sim

Otsu_Obs

2km 2mile

Lake Shinji

Subbasin 34 Subbasin 22 Subbasin 42 Subbasin 33

Subbasin 6

Subbasin 14

Subbasin 13

Subbasin 8 Subbasin 1 Subbasin 2

River or ditch

Highway Road

Target river

00.10.20.30.40.50.60.70.80.9

1988

1989

1990

1991

1992

1993

1995

1996

1997

1998

1999

2000

2002

2003

2004

2005

2006

2007

2009

2010

2011

Disc

harg

e cm

s

Flow6_Sim

0

0.05

0.1

0.15

0.2

0.25

0.3

1988

1989

1990

1991

1992

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1996

1997

1998

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2011

Disc

harg

e cm

s

Flow2_Sim

00.05

0.10.15

0.20.25

0.30.35

0.40.45

0.5

1988

1989

1990

1991

1992

1993

1995

1996

1997

1998

1999

2000

2002

2003

2004

2005

2006

2007

2009

2010

2011

Disc

harg

e cm

s

Flow1_Sim

00.10.20.30.40.50.60.70.80.9

1988

1989

1990

1991

1992

1993

1995

1996

1997

1998

1999

2000

2002

2003

2004

2005

2006

2007

2009

2010

2011

Disc

harg

e cm

s

Flow8_Sim

00.05

0.10.15

0.20.25

0.30.35

0.40.45

0.5

1988

1989

1990

1991

1992

1993

1995

1996

1997

1998

1999

2000

2002

2003

2004

2005

2006

2007

2009

2010

2011

Disc

harg

e cm

sFlow14_Sim

00.05

0.10.15

0.20.25

0.30.35

0.40.45

1988

1989

1990

1991

1992

1993

1995

1996

1997

1998

1999

2000

2002

2003

2004

2005

2006

2007

2009

2010

2011

Disc

harg

e cm

s

Flow13_Sim

00.10.20.30.40.50.60.70.8

1988

1989

1990

1991

1992

1993

1995

1996

1997

1998

1999

2000

2002

2003

2004

2005

2006

2007

2009

2010

2011

Disc

harg

e cm

s

Flow42_Sim

0

0.5

1

1.5

2

2.5

1988

1989

1990

1991

1992

1993

1995

1996

1997

1998

1999

2000

2002

2003

2004

2005

2006

2007

2009

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2011

Disc

harg

e cm

s

Flow33_Sim

00.20.40.60.8

11.21.41.61.8

2

1988

1989

1990

1991

1992

1993

1995

1996

1997

1998

1999

2000

2002

2003

2004

2005

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2011

Disc

harg

e cm

s

Flow34_Sim

0

0.5

1

1.5

2

2.5

3

1988

1989

1990

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2011

Disc

harg

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Flow22_Sim

Simulated flow discharge from small river basins

Field investigation To calibrate model parameter values,

we’ve started measuring flow

and collecting water samples

Preliminary calculation of nutrient load discharges from small river basins

0.00

0.50

1.00

1.50

2.00

2.50

6 2 1 8 14 13 42 33 34 22 43

Annual TN Load

0.00

0.10

0.20

0.30

0.40

6 2 1 8 14 13 42 33 34 22 43

Annual TP Load

Annual TN load (tons/km2/year) Annual TP load (tons/km2/year)

Hii River (No.43)

In unit load discharges, Subbasin Nos. 6, 8, 13 (Northern part of Lake Shinji) showed higher values in the watershed

Annual loads per area vary from 0.70 (34) to 2.2 (6) tons/km2 in TN, and from 0.043 (43) to 0.33 (6) tons/km2 in TP.

Preliminary calculation of nutrient load discharges from small river basins

Annual Total TN load (tons/year) Annual Total TP load (tons/year)

10% 20%

0

200,000

400,000

600,000

800,000

1,000,000

1,200,000

Hii River Other 10 Rivers0

10,000

20,000

30,000

40,000

50,000

Hii River Other 10 Rivers

Annual total loads occupy about 10 % of TN and 20% of TP of annual total loads from Hii River basin.

10 river basins were considered in this preliminary calculations, and it was revealed that total load discharges from small river basins are relatively large though each load discharge from a small river basin is small

Conclusion We are trying to evaluate discharges of flow and nutrient loads from small river basins around the Lake Shinji for considering conservation ways of water environment

SWAT could represent flow discharges “Satisfactory” from 1988 to 2011 in Monthly basis (in the future, daily basis)

SWAT could make flow discharges of small river basins around the lake (they need to be calibrated later, though)

From the preliminary calculation of averaged annual TN and TP loads from small rivers, it is considered that total loads from small river basins may have large influences in total, though Hii River basin still has a larger impact to the lake water environment

Future Plan Calibrate parameter values of small river basins Input monthly load discharges from the rural community

sewerage Scenario analysis, especially pay attention to forestry of

artificial coniferous forest

Impact assessment of river basins against the Lake Shinji water environment

Lake Shinji Lake Nakaumi

Location of rural community sewerage in / around the study area

Relatively high concentration of

nutrient discharges to rivers

Future analysis

TN: 5.6 mg/L (n:5) TP: 2.2 mg/L (n:5)

Inside of a forest (for example) Rough management

Higher concentration of water discharged from a rough management forest

T-N濃度の変動

0

0.5

1

TN(1)TN(2)

site2 間 間Thinning

Concentration (mg/L)

site 1 間 間Thinning

1999 2001 2003

TN(1) : Forest under delay thinning TN(2) : Forest under well management

（Analyzed by Prof. Takeda）

Thank you very much for your attention

27

0

200

400

600

800

1000

1200

1400

Q (Hii R.) V (L. Shinji) V (L. Nakaumi)

wat

er v

olum

e (1

06m

3 )

Annual discharge

Water Volume of Hii River ,and Lakes Shinji and Nakaumi

51,000

41,000

28,400

0

10,000

20,000

30,000

40,000

50,000

60,000

1992 1997 2002

Number of employed persons by age and population changes in agriculture and forestry employment (Shimane Prefecture)

しまね統計情報データベースより http://www.toukeika.pref.shimane.jp/toukei/st0/st0100.asp

・Working population in agriculture and forestry has declined

According to the Census of Agriculture and Forestry, Agriculture：54,651 households （1995）→49,480 households（2000） -9.5% Forestry：38,335 households （1990）→36,379 households（2000） -5.1%

population changes in agriculture and forestry employment

・Most of the workers are 65 years old or older

Popu

latio

n

Number of employed persons by age

0 200 200 400 200 900 8001,700 2,100

3,400

18,700

02,0004,0006,0008,000

10,00012,00014,00016,00018,00020,000

Popu

latio

n

Hii River basin : Major contributor for the downstream lake water environment because it occupies about 75 % of watershed area of Lake Shinji

For more accurate impact assessment of river basins against lake water environment, it is nece

土地利用更新・・・森林の影響をみるため DEM更新・・・河道網を正確に引くため