sediment yield estimation from a hydrographic survey: a
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Sediment yield estimation from a Sediment yield estimation from a hydrographic survey: A case study hydrographic survey: A case study for the for the KremastaKremasta reservoir, Western reservoir, Western GreeceGreece
D. D. ZarrisZarris(1)(1), E. , E. LykoudiLykoudi(2)(2) & D. & D. KoutsoyiannisKoutsoyiannis(1)(1)
(1) (1) Department of Water Resources, Faculty of Civil Engineering, NatDepartment of Water Resources, Faculty of Civil Engineering, National Technical ional Technical University of Athens, 5 University of Athens, 5 HeroonHeroon PolytechneiouPolytechneiou St., Athens 15780, GreeceSt., Athens 15780, Greece(2) Department of Geological Sciences, Faculty of Mining Enginee(2) Department of Geological Sciences, Faculty of Mining Engineering and ring and Metallurgy, National Technical University of Athens, 5 Metallurgy, National Technical University of Athens, 5 Heroon PolytechneiouHeroon Polytechneiou St., St., Athens 15780, GreeceAthens 15780, Greece
55thth International Conference International Conference “Water Resources “Water Resources Management in the Era of Transition”Management in the Era of Transition”, Athens, 4, Athens, 4--8 8 September 2002September 2002
Brief Outline of the PresentationBrief Outline of the Presentation
Introduction (Sediment yield and delivery processes, sediment accumulation in reservoirs, source erosion)
Research Project
Appraisal of river sediment deposits in reservoirs of hydropower dams, Funded by Public Power Corporation (PPC) and the General Secretariat of Research and Technology (GSRT), 1998-2001
Research method (Hydrographic survey of the Kremastareservoir, Western Greece)
Computation of total mass of the deposited sediments for the total period of the reservoir’s operation
Catchment’s sediment yield and delivery ratio estimation
Comparison with other published data from the international literature
Sediment delivery processesSediment delivery processesSediment source (wash load versus river bed material)
Magnitude and proximity to the outlet of the source erosion areasCharacteristics of the drainage network (density and frequency, slope gradients, watershed area)Frequency, intensity and duration of the erosion producing storms (wash load)Geological formations and soil characteristics (erodibility)Geomorphologic characteristics (faults, orographic uplifting, etc.)Depositional potential of the catchment (surface roughness, depressions, man-made sediment storages)
Sediment yield processesSediment yield processes
Temporal variability both in annual yields but also in inter-storm amounts
Sediment yield estimates...
1. Simple statistical regression models (e.g. sediment rating curves, sediment yield with catchment area)
Sediment yield processes as functions of spatial scale (e.g. vegetation cover for hillslope scales and partial rainfall coverage and drainage density to watershed scales)
Strongly influenced, but not completely determined, by watershed area
2. Conceptual or physically-based mathematical models (e.g. LISEM, WEPP, EUROSEM)
3. Reservoir deposits’ measurements by (repeated) hydrographic surveys
Sediment yield characteristics...
Precise processes still unknown, lack of mathematical expression with universal applicability
Temporal variability of sediment dischargesTemporal variability of sediment dischargesSediment discarge vs discharge measurments in Aliakmonas R.
at Ilarionas, Northern Greece
0,1
1
10
100
1000
10000
1 10 100 1000Discharge (m 3 /s)
Sedi
men
t dis
char
ge (K
gr/s
)
Dry period
W et period
Spatial variability of sediment yield Spatial variability of sediment yield (lack of universal expression)(lack of universal expression)
1
10
100
1000
10000
100 1000 10000 100000
Area (km2)
Sedi
men
t yie
ld (t
/km
2Data from 42 Data from 42 international watershedsinternational watersheds
KremastaKremasta reservoir watershedreservoir watershed
LANDSAT 7 (ETM+) ImageCatchment drainage network
KremastaKremasta reservoir watershed reservoir watershed ((contcont.).)
Digital Terrain Model (DTM) Mean annual rainfall (mm)
KremastaKremasta reservoir watershed reservoir watershed ((contcont.).)
Land usesGeologic formations
KremastaKremasta reservoir hydrographic surveyreservoir hydrographic survey
Positioning: Differential Global Positioning System (DGPS) (reference station and moving receiver) with accuracy in horizontal plane 2-5 m(1)
Additional information...
Dionysos Satellites Centre, Department of Topography, Faculty of Surveying and Rural Engineering, National Technical University of Athens
Distance between echo-sounding routes ranging from 50 to150 m, additionally to check routesDepth measurement: Hydrographic echo-sounder Raytheon DE 719B operating at the frequency of 200 kHz(2)
2. Depth measurement error: 0.5%±1 in of the total depthValuable contribution by...
1. In level of significance 95% with selected availability
Depth measurement illustrationDepth measurement illustration
Hydrographic Hydrographic routes for routes for reservoir reservoir scanningscanning
DTM Generation and Calculation of DTM Generation and Calculation of Deposits’ VolumeDeposits’ Volume
Digitization of initial topographic maps
Scale 1:5000
Extraction of spatially irregularmesh of points and creation
of the Triangulated Irregular Network (ΤΙΝ)
Grid formation
size 6 m*6 m
Algorithm:Triangulation with linear interpolation
(SURFER 7.0)Union of DGPS files and echo-sounder entries
in one uniqueASCII file
Creation of the TIN surface and grid formation
size 6 m*6 m
INITIAL TOPOGRAPHIC MAPSINITIAL TOPOGRAPHIC MAPS
HYDROGRAPHIC SURVEYINGHYDROGRAPHIC SURVEYING
Typical errors of hydrographic surveyingTypical errors of hydrographic surveying
DGPS accuracy on horizontal plane (due to selected availability)Obscure definition of the water-mud interfaceVariation of the hydrographic boat speed
Digitization errors both of the initial topographic maps but also from the echo-sounder charts
Errors in x-y-z plane from the construction of the initial topographic maps prior to the dam construction
Significant non-typical error (uncertainty): Areas as earth material banks for dam construction not known
Indicative profile of fluvial sediment Indicative profile of fluvial sediment deposits (a)deposits (a)
245
255
265
275
-5000 -4980 -4960 -4940 -4920 -4900 -4880 -4860 -4840Longitude (m)
Lev
el (m
)
Prior to the dam construction
Year of the hydrographic survey
Section near the reservoir delta at Acheloos R. branch
Indicative profile of fluvial sediment Indicative profile of fluvial sediment deposits (b)deposits (b)
160
180
200
220
240
260
280
300
4900 5100 5300 5500 5700 5900 6100 6300 6500
Longitude (m)
Lev
el (m
)
Prior to the dam construction
Year of the hydrographic survey
Section at the inner part of the reservoir
Identification Identification of reservoir of reservoir segments with segments with sediment sediment deposits (a)deposits (a)
Identification Identification of reservoir of reservoir segments segments with with sediment sediment deposits (b)deposits (b)
Deposits
Deposits
Deposits
Non-Deposits
ResultsResults –– Deposits’ VolumeDeposits’ Volume
10.466.6TOTAL
2.212.2MEGDOVAS R.
2.513.1AGRAFIOTIS R.
5.741.3ACHELOOS R.
Deposits’ area(km2)
Deposits’ Volume(hm3)
Reservoir Sections
INITIAL DESIGN STUDY INITIAL DESIGN STUDY ESTIMATE FOR DESIGN ESTIMATE FOR DESIGN
PERIOD 50 YEARSPERIOD 50 YEARS394394 hmhm33
Results Results –– Deposits’ MassDeposits’ Mass
Undisturbed samples were impossible to be collected due to the physical properties of the deposited sediments
Collection of two core samples from the reservoir’s invert• Evaluation of deposits’ thickness• Analysis of sediments physical characteristics and mineral composition• Estimation of deposits’ density• Estimation of real deposition rate• Measurement of sediment organic content
Additional Information...
(1) Lane and Kolzer formula from percentage quantities of sand, silt and clay(correspondingly 71.9% sand, 23.3% silt and 4.8% clay)
(2) Density estimation after 34 years of reservoir operation 1692 kg/m3
TOTAL DEPOSITS’ MASSTOTAL DEPOSITS’ MASS112.5 112.5 MtMt
ACHELOOSACHELOOS AGRAFIOTISAGRAFIOTIS MEGDOVASMEGDOVAS69.869.8 Mt 22.1 Mt 20.6 MtMt 22.1 Mt 20.6 Mt
Sediment yield of Sediment yield of KremastaKremasta reservoir reservoir watershedwatershed
TOTAL
MEGDOVAS R.
AGRAFIOTIS R.
ACHELOOS R.
Subcatchment
3292106.41005.6
123919.5489.4
32020.92034.8
173366.01184.6
Subcatchment area
A (km2)
Mean annual sediment dischargeQs (kg/s)
Mean annual sediment yield
Sy (t/km2)
Comparison with internationally published dataComparison with internationally published dataa) Sediment yielda) Sediment yield
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1
10
100
1000
10000
100 1000 10000 100000Area (km2)
Sedi
men
t yie
ld (t
/km
2)
Agrafiotis R.Acheloos R.
Megdovas R.
Data from Dendy and Bolton (1976)
Comparison with internationally published data Comparison with internationally published data b) Sediment delivery ratiob) Sediment delivery ratio
0 .0 0
0 .1 0
0 .2 0
0 .3 0
0 .4 0
0 .5 0
1 0 0 1 0 0 0 1 0 0 0 0 1 0 0 0 0 0
A re a (k m2)
Del
iver
y ra
tio
A grafio tis R .
A che loo s R .
M e gdovas R .
Laure nce , 1996
R e nfro , 1972
Soil erosion and sediment delivery ratio Soil erosion and sediment delivery ratio estimationestimation
0.2050401005.6TOTAL
0.222251489.4MEGDOVAS
0.4248472034.8AGRAFIOTIS
0.1770771184.6ACHELOOS
Sediment delivery ratio
Soil erosionΑ (t/km2/y)
Mean annual sediment yield
Sy (t/km2)Subcatchment
Soil erosion computed from a GIS based modelof the Universal Soil Loss Equation (USLE)
ConclusionsConclusions
Measurements of deposited sediments within a reservoir could be an effective method for reconstructing long term catchment sediment yieldsThe reservoir under study should be large enough so that trap efficiency could be assumed as unity This method is unable to estimate sediment yield of finer time scales (e.g. annually) unless more frequent hydrographic surveys are accomplished This method combined with sediment discharge measurements in an upstream site and/or alternative measurement techniques (e.g. turbidity) can be an effective tool on integrated catchment management
ConclusionsConclusions ((cont.cont.))
Dead volume principle, at least for large reservoirs, should be reconsidered in terms of the spatial accumulation of deposited sediment as describedCatchment sediment yields under study exhibit considerably higher values than other published data from throughout the globeGeomorphologic controls such as tectonic activity, orographic uplifting, hydrological parameters (e.g. intense storms) and also the dominant geological formation (e.g. highly erodible flysch) are responsible for this considerable difference
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