1. ESTIMATE OF SEDIMENTATION IN KALAVASOS RESERVOIR, CYPRUS
TENTH INTERNATIONAL SYMPOSIUM ON RIVER SEDIMENTATION MOSCOW, RUSSIA, AUGUST 1-4, 2007
ESTIMATE OF SEDIMENTATION
IN KALAVASOS RESERVOIR, CYPRUS
V. HRISSANTHOU AND M. ANDREDAKI
DEPARTMENT OF CIVIL ENGINEERING
DEMOCRITUS UNIVERSITY OF THRACE
67100 XANTHI, GREECE

2. INTRODUCTION
Computation of sedimentation in Kalavasos Reservoir in terms of soil erosion in the corresponding basin
Kalavasos Reservoir is located northeast of the town of Limassol, Cyprus
Storage capacity of the reservoir: m³
Water surface area of the reservoir: m²
Basin area of the reservoir: 96 km²
Main stream of the basin: Vasilikos River
A mathematical model is used for the computation of the mean annual reservoir sedimentation

3. MATHEMATICAL MODEL Three submodels: Hydrological submodel
Soil erosion submodel (Poesen, 1985)
Stream sediment transport submodel (Yang and Stall, 1976)
The calculations are performed on a monthly time basis

4. HYDROLOGICAL SUBMODEL
Simplified water balance model for the root zone of the soil:
Sn´ = Sn-1 + Nn - Ern
S: available soil moisture [mm]
N: rainfall amount [mm]
Er: actual evapotranspiration [mm]
n: index for the time step

5. HYDROLOGICAL SUBMODEL
If Sn´<0, then Sn=0, hon=0, INn=0
If 0≤Sn´≤Smax, then Sn=Sn´, hon=0, INn=0
If Sn´>Smax, then Sn=Smax, hon=K(Sn´-Smax), INn=K´(Sn´-Smax)
where K´=1-K
ho: direct runoff [mm]
IN: deep percolation [mm]
Smax: maximum available soil moisture [mm]
K, K´: proportionality coefficients

6. SOIL EROSION SUBMODEL (Poesen, 1985)
qrs = C(KE)rs-1cosa
qr = qrs[0.301sina+0.019D (1-e-2.42sina)]
qrs: mass of detached particles per unit area [kg/m2]
C: soil cover factor
KE: rainfall kinetic energy [J/m2]
rs: soil resistance to drop detachment [J/kg]
a: slope gradient [o]
qr: downslope splash transport per unit width [kg/m]
D50: median particle diameter [m]

7. SOIL EROSION SUBMODEL qf = rqt (Nielsen et al., 1986)
qf: sediment transport by runoff per unit width [m3/(s m)]
r: entrainment ratio (r=1 for noncohesive soils, r<1 for cohesive soils)
qt: sediment transport capacity by overland flow per unit width
[m3/(s m)]

8. qt = [0.04(2g/f)1/6q5/3s5/3] / [(ρs/ρ-1)2g1/2D50]
SOIL EROSION SUBMODEL
qt = [0.04(2g/f)1/6q5/3s5/3] / [(ρs/ρ-1)2g1/2D50]
(Engelund and Hansen, 1967)
g: gravity acceleration [m/s2]
f: friction factor
q: runoff rate per unit width [m3/(s m)]
s: energy slope
ρs: sediment density [kg/m3]
ρ: water density [kg/m3]

9. If qrf > qt, then ES = qt If qrf < qt, then ES = qrf
SOIL EROSION SUBMODEL
Available sediment on the soil surface of a sub-basin (qrf) =
downslope splash transport (qr) + sediment transport by runoff (qf)
Estimation of sediment ES reaching the main stream from the
respective sub-basin area
If qrf > qt, then ES = qt
If qrf < qt, then ES = qrf
qt: sediment transport capacity by overland flow

10. STREAM SEDIMENT TRANSPORT SUBMODEL
Estimation of sediment load FLO at the outlet of the main stream
of a sub-basin
If ESI > qts, then FLO = qts
If ESI < qts, then FLO = ESI
ESI: available sediment load in the main stream considered
qts: sediment transport capacity by streamflow

11. STREAM SEDIMENT TRANSPORT SUBMODEL
logct= log(wD50/ν)-0.457log(u*/w)+
+[ log(wD50/ν)-0.314log(u*/w)]log(us/w-ucrs/w)
(Yang and Stall, 1976)
ct: total sediment concentration by weight [ppm]
w: terminal fall velocity of suspended particles [m/s]
D50: median particle diameter of bed material [m]
ν: kinematic viscosity of the water [m2/s]
u: mean flow velocity [m/s]
ucr: critical mean flow velocity [m/s]
u*: shear velocity [m/s]
s: energy slope

12. APPLICATION OF THE MATHEMATICAL MODEL
Basin of Kalavasos Reservoir:
Area: 96 km2
Main stream length: 18 km
Soil cover: forest (87.7%), bush (2.7%), urban area (0.9%),
cultivated land (8.3%), no significant vegetation (0.4%)
Permeable soils: 23.4%, semi-permeable soils: 76.6%
Highest altitude: 1300 m

13. Division of Kalavasos Reservoir basin into 5 natural sub-basins

14. AVAILABLE DATA
Monthly rainfall data for 16 years (1986 – 2001) from 7 rainfall stations (mean annual rainfall amount 572 mm)
Mean daily values of air temperature, relative air humidity, sunlight hours and wind velocity for every month of the 16 years from 1 meteorological station
Symbols:
YD: annual erosion amount in the basin [t]
YA: annual sediment yield at the basin outlet [t]
DR: sediment delivery ratio (YA/YD)

15. COMPUTATIONAL RESULTS
Year
YA [t]
YD [t]
DR [%]
1986
4200
4300 98
1987
74 000 38
1988
72 000 58
1989
44 000
65 000 68
1990
40 000
51 000 78
1991 32

16. COMPUTATIONAL RESULTS
Year
YA [t]
YD [t]
DR [%]
1992
50 000
60 000 83
1993
25 000
30 000
1994 53
1996
41 000
52 000 79
1999
1400
100
2000
20 000
2001
65 000 44

17. COMPUTATIONAL RESULTS
Mean value of YA: t
Mean value of YD: t
Mean value of DR: 70%
Mean annual rate of soil erosion: 0.44 mm (computation)
0.50 mm (measurement)
(Water Development Department, Nicosia, Cyprus)
Trap efficiency of Kalavasos Reservoir: 100%
Mean annual deposition volume in the reservoir: m³
Useful life of the reservoir: 556 years

18. SENSITIVITY ANALYSIS

19. SENSITIVITY ANALYSIS

20. CONCLUSIONS
The soil erosion submodel underestimates slightly the measured mean annual rate of soil erosion for the whole basin.
The input data of the mathematical model, that influence the annual erosion amount of the whole basin and the annual sediment yield at the basin outlet more strongly than the other input data, are the rainfall amount, the curve number, the sub-basin areas and the soil slope gradient of the sub-basins.
There is not an immediate and sharp danger of reservoir filling with sediments.