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Environmental Hydrodynamics in Lakes and Reservoirs
M. Umeda (Tohoku University)
Introduction
500mhttp://maps.google.co.jp
For the group of Water Quality, Tuni Reservoir = one of Main Research Objects
Condoriri
HPW
Tuni
Tuni Dam
Today’s Presentation:Basic Methods from our previous studies in Lakes and Reservoirs.
Tuni Reservoir Basin of Tuni Reservoir
Measurements in Miharu Reservoir
Miharu Reservoir
Sendai
General Information
Capacity: 4.2×106 m3
Catchment: 226.4 km2
Purpose: Flood control, Water supply, Industrial water,Irrigation, Power generation
Eutrophication Problems Water Bloom, every summer(cyanobacteria)
Field Measurements in a Reservoir
A B
C
D
Plan view of Miharu What we measure:
a) StratificationThermal stratification,Vertical distribution of WQ
b) Temporal change of WQwater temperature,DO, Chlorophyll-a, etc.
c) Deposition fluxIncluding Sediment,Detritus, etc.
0 1.0 kmDam
Anchor
Thermocline
Sediment traps
Self-recording device
Buoy
Buoy
Sediment traps
Sediment traps
Field Measurements in a Reservoir
a) Stratification (Vertical distribution)
b) Temporal change of WQ
c) Deposition flux
How we measure:
Hanging and sinking sensorsfrom a boat.
Deploying self-recording devices on ropes with floats
Using sediment trapsdeployed
Examples of Results - In Miharu Reservoir-
0 10 2030
20
10
0
0 5 10 15
0 10 2030
20
10
0
0 5 10 15
0 10 2030
20
10
0
0 5 10 15WT [oC]Turbidity
Chl-a [µg/l]DO [mg/l]
Dep
th [m
]D
epth
[m]
Dep
th [m
]a) Stratification (Vertical distribution) Aug. 5,
2008
Aug. 14,2008
Sep. 5,2008
Turbidity
Water temp.
Chlorophyll-a
DO
300
310
320
300
310
320
300
310
320
02040
048
12
0102030
WT
[o C]
DO
[mg/
l][F
TU]
Alti
tude
[m]
Alti
tude
[m]
Jan. Dec.Apr. Aug.
b) Temporal change of WQ(Measurement by the Dam Office, MLIT)
History of vertical distributions
WaterTemp.
DO
Turbidity
Hydraulic Numerical ModelingSolvers are selected depending on requirements:
1-dimensional (vertical)2-dimensional (vertical)3-dimensional
Spatial Resolution
Water temperatureTurbiditySalinityChlorophyll-a (phytoplankton)Nutrients (Phosphorus, Nitrogen)Dissolved Oxygen
Variables
Simple, but sometimes givesmore realistic solution than higher dimension analysis
related to density structure.
related to eutrophication.
Example of Computation
InflowOutflow
Conceptual diaguram of Vertical 1-D Model
Vertical 1-D Modeling in a coastal lagoon
0 1 2km
Lake Jusan
Lake Jusan:Facing the Japan SeaVery shallow lagoon:
Mean depth = 1m
Famous for product of shelfish
Results: Validation of Time Series
0102030
0102030
05
10
0100200300
6/9 8/57/7 9/1
DO[mg/l]
Salinity 1[psu]
Discharge[m3/s]
Salinity 2[psu]
Blue line: MeasurementRed line: Computation
Vertical 1-D computation
Results: History of Vertical Structure
Jun. 9 Jul. 7 Aug. 5 Sep. 1 Oct. 6
−1
0
1
Ele
vati
on[m
]
DO
−1
0
1
Ele
vati
on[m
]
Salinity
Vertical 1-D computation Freshwater(white)
Saline water(blue)
High DO(white)
Low DO(Red)
Numerical ModelingSolvers are selected depending on requirements:
1-dimensional (vertical)2-dimensional (vertical)3-dimensional
Spatial Resolution
Water temperatureTurbiditySalinityChlorophyll-a (phytoplankton)Nutrients (Phosphorus, Nitrogen)Dissolved Oxygen
Variables
Most often used in practical works
related to density structure.
related to eutrophication.
Method of 2-D analysis
outflow
InflowWater temp. Velocity
Vertical 2-D Reservoir Hydrodynamic Model
Governing Equations•Momentum Eq.•Continuity Eqs•Transport Eqs of scalars•K-ε turbulence model Eqs
The most typical modeling for reservoirs.
( ) ( ) 0uB wBx z∂ ∂
+ =∂ ∂
1 1L eff
u u u p u uu v B Bt x y x B x x z z
ν νρ
∂ ∂ ∂ ∂ ∂ ∂ ∂ ∂ + + = − + ∂ ∂ ∂ ∂ ∂ ∂ ∂ ∂
, etc..
Including the bathymetry effect of breadth B.
10 20 30 40 50 60
UpstreamDam
SS [mg/l]
0 0.5 1 1.5
260
280
300
320
Alti
tude
(m)
Distance (km)
Longitudinal & Vertical Distribution of Suspended Sediment
From an Investigation of High Turbidity ProblemCaused by Flood Water Intrusion
0
20
40
60
00.010.020.030.04
00.5
11.5
2
Water Quality in Miharu Reservoir
May July Sep.
Chlorophyll – a(µg/l)
Lines: Computation, Dots: Measurement
Inorganic Phosphorus
(mg/l)
Inorganic Nitrogen
(mg/l)
2008
Summary
• Basic research methods for environmental hydraulics in lakes and reservoirs were presented.
• Field measurements in Miharu Reservoir was shown as a typical example.
• Water quality numerical modeling s in a coastal lagoon (case of 1-D) and a reservoir (2-D) were demonstrated.
