Detailed mapping of precipitation, forecasting of extreme rainfall events, and water balance investigation in the Mornos reservoir
Dr Vasso Kotroni (National Observatory of Athens)
Dr Costas Lagouvardos (National Observatory of Athens)
Dr Ilias G. Pechlivanidis
The Athens Water Supply and Sewerage Company (EYDAP SA) has funded an initiative to instrument and measure at a fine spatial-temporal resolution the hydrological fluxes (e.g. rainfall, snowfall, streamflow, potential evaporation) of the 560 km2 Mornos catchment that supplies the metropolitan area of Athens, Greece, with fresh water. This project will further investigate the hydrological response of the catchment and estimate the water balance in the Mornos reservoir; and hence it will allow the assessment and monitoring of the leaks in the reservoir. Overall, our expectations focus on: i) improving the management of the reservoir, based on an integrated system of local observations and numerical simulations, which will operate on a daily basis, and ii) keeping a record of the temporal evolution of the leaks in the reservoir.
My duties include: i) field work – measure river velocities and generate water level – discharge curves (rating curves), ii) development of GIS-based tools to simulate the hydrological cycle at the regional scale, and iii) use of developed tools for hydrological forecasting under uncertainty.
Ilias developed tools based on the SCS-CN method to simulate hydrographs in continuous time from empirical equations relating parameters for time of concentration, time lag, abstractions, runoff coefficient, and curve number, which further depend on surface slope, soil and land use. Consequently, the models require information from DEMs, land use and soil properties. In total, three SCS-CN based models of various sophistication and complexity have been applied: the traditional SCS-CN method, the simplified SAHU model, and the Mishra-Singh model.
Water budget model
In this application, a simple and parsimonious water budget model related to the degree of physical representation of fluxes is set. The model conceptualised for the reservoir of Mornos takes the following form:
PL,t + Qint + Qevinost + GWt – Et – Qoutt – Qoverflowt = ΔStorage
where PL is the rainfall that falls directly into the lake, Qin is the streamflow that contributes to the reservoir, Qevinos is the water volume imported from Evino's connecting tunnel, GW is the groundwater contribution, E is the evaporation from the reservoir, Qout is the discharge distributed to the city of Athens, Qoverflow is the discharge due to overflowing water, and ΔStorage is the change in the water storage of the reservoir.
Most of the above components can be estimated using measured and simulated data. Qin is estimated in a daily step according to the SCS-CN rainfall-runoff model presented above. Discharge data from the Evinos River (Qevinos) will be given from EYDAP, whereas evaporation in the lake is estimated from the evaporation pan installed right next the dam. The amount of water distributed to the city of Athens is measured; hence Qout data are available. Ground water contribution is difficult to be estimated, and will be estimated given that the remaining terms of the equation above are known.