UNESCO WORKSHOP Integrated Urban Water Management in TC Temperate Climates Belgrade 15-16 May 2006 Managing water supply resources in karstic environment (temperate climate) E. Rozos, D. Koutsoyiannis Department of Water Resources School of Civil Engineering National Technical University of Athens
Presentation structure Historical flashback The Athens water supply system as a case study The Boeoticos Kephisos basin (a karst basin) Hydrological modelling Water resources management Results Conclusions Managing water supply resources in karstic environment 2
Historical flashback Throughout history, karstic aquifers have had an important role in urban development around the Mediterranean. In ancient Athens (a great example of sustainable water management), water supply was based on two main aqueducts, the Peisistratean and the Hadrianian (partly functioning till today), conveying water from karstic springs at foothills of surrounding mountains. Peisistratean aqueduct uncovered during the excavations for the Metro. Hadrianian aqueduct maintenance in 1929. Managing water supply resources in karstic environment 3
Athens water supply system Important karstic aquifers in modern times Extended karstic aquifers Managing water supply resources in karstic environment 4
Boeoticos Kephisos water basin Abstractions for water supply Vassilika boreholes abstract water from karstik aquifer that discharges to Mavroneri springs. Managing water supply resources in karstic environment 5
Boeoticos Kephisos water basin Abstractions for irrigation IW IW Sluice gates (irrigation) IW IW IW: Pumping wells (irrigation) Managing water supply resources in karstic environment 6
Karstic aquifer peculiarities Water basin model The design of a hydrological model of a water basin which includes karstic aquifers should take account of the following: 1.Karstic aquifers have great interaction with surface water (conjunctive simulation). 2.Karstic aquifers have small response times (good description of human intervention, e.g. abstractions) 3.Karstic aquifers may have significant influence to basin budget by importing/leaking water from/to other basins. 4.Karstic conduits network is irregular and difficult to describe; therefore it is preferable to be modelled using a conceptual (rough) approach. Managing water supply resources in karstic environment 7
Water basin model Conjunctive simulation Surface model Modified Thornthwaite soil moisture model Groundwater model Modified multicell model Hydrosystem model Digraph representation Managing water supply resources in karstic environment 8
Water basin model Surface model Managing water supply resources in karstic environment 9
Water basin model Surface model Permeability High (karst) Med. (alluv.) Low (flysch) HRU=Permeability U Slope Slope High Low Managing water supply resources in karstic environment 10
Water basin model Groundwater model Representation of flow with a hydraulic analogous. Flow in pipes may be described with Darcy or non Darcy equations. Managing water supply resources in karstic environment 11
Water basin model Groundwater model Limited number of cells. Large cells in areas with mild hydraulic gradient. Leakages from karstic conduits to the adjacent sea. Managing water supply resources in karstic environment 12
Water basin model Hydrosystem model Topology river, aqueduct, pumping capacities, demand areas, connectivity Input surface and spring runoff water needs Parameters constraints priorities unit cost values Managing water supply resources in karstic environment 13
Water basin model Karstic formations, and pumping wells for irrigation Well abstractions from karstic aquifers influence directly the behavior of corresponding springs. Accurate estimation of well abstractions for irrigation are imperative. Managing water supply resources in karstic environment 14
Water basin model Surface hydrology model Surface runoff Hydrosystem model Infiltration Well abstractions Estimate well abstractions Deficit between surface+baseflow and needs is covered with pumps. Pumps effect on baseflow Less baseflow results in need form more pumping. Groundwater model Baseflow (spring discharge) Baseflow NO Baseflow stabilisation YES END Managing water supply resources in karstic environment 15
Water basin model Simulated spring discharge, basin outlet Mavroneri Sim. Mavroneri Obs. Oct-93 Oct-92 Oct-91 Oct-90 Oct-89 Oct-88 Oct-93 Oct-92 Oct-91 Oct-90 Oct-89 Oct-88 Managing water supply resources in karstic environment 16 Oct-87 Oct-87 Oct-86 Oct-86 Oct-85 Oct-85 Oct-84 Oct-84 4 3 2 1 0 40 30 20 10 0 Basin outflow Sim. Basin outflow Obs. m 3 /s m 3 /s
Estimated water budget Water basin model Leaks 25% Mean annual precipitation 1575 hm 3. Evapotranspiration 48% Abstractions 13% Outflow 14% Managing water supply resources in karstic environment 17
Water supply system characteristics Water resources management Evinos reservoir Mornos reservoir 630 hm 3 112 hm 3 Lake Yliki 585 hm 3. Leaks (level depended) through karstic conduits Marathon reservoir 32 hm 3 Mornos aqueduct 188 km (gravity flow) Yliki aqueduct 67 km (pumps) Managing water supply resources in karstic environment 18
Water supply system schematisation Digraph representation Minimize cost function with Simplex algorithm Water resources management Managing water supply resources in karstic environment 19
Results Parametric rules for reservoirs system control (scenario 1 medium demand) Target storage (hm 3 ) Yliki 400 Mornos Water from Yliki is used with low priority to reduce cost Evinos 120 80 System storage (hm 3 ) Managing water supply resources in karstic environment 20
Results Parametric rules for reservoirs system control (scenario 2 high demand) Target storage (hm 3 ) Mornos Yliki Water from Yliki is used with high priority to reduce losses Evinos System storage (hm 3 ) Managing water supply resources in karstic environment 21
Conclusions 1. In water basins with extended karst formations conjunctive surface water and groundwater simulation is compulsory. 2. Accurate physically based modelling of karst aquifers may be infeasible; however, a conceptual approach may suffice. 3. The water exchange between adjacent karst basins and the leakage to the sea may be a significant component of the water budget and requires a careful approach. 4. Good description of the human intervention (e.g. of well abstractions) in karstic aquifers may improve noticeably the model performance. 5. The management of a hydrosystem including some karst areas should be holistic; for example, karst formations in a single reservoir influence greatly the operation rules of the whole system. Managing water supply resources in karstic environment 22
References Efstratiadis, A., G. Karavokiros, S. Kozanis, A. Christofides, A. Koukouvinos, E. Rozos, N. Mamassis, I. Nalbantis, K. Noutsopoulos, E. Romas, L. Kaliakatsos, A. Andreadakis, and D. Koutsoyiannis, The ODUSSEUS project: Developing an advanced software system for the analysis and management of water resource systems, 3nd General Assembly of the European Geosciences Union, Geophysical Research Abstracts, Vol. 8, Vienna, 03910, European Geosciences Union, 2006. Efstratiadis, A., E. Rozos, A. Koukouvinos, I. Nalbantis, G. Karavokiros, and D. Koutsoyiannis, An integrated model for conjunctive simulation of hydrological processes and water resources management in river basins, 2nd General Assembly of the European Geosciences Union, Geophysical Research Abstracts, Vol. 7, Vienna, 03560, European Geosciences Union, 2005. Efstratiadis, A., I. Nalbantis, and E. Rozos, Model for simulating the hydrological cycle in Boeoticos Kephisos and Yliki basins, Modernisation of the supervision and management of the water resource system of Athens, Report 21, 196 pages, Department of Water Resources, Hydraulic and Maritime Engineering - National Technical University of Athens, Athens, January 2004. Karavokiros, G., A. Efstratiadis, and D. Koutsoyiannis, Hydronomeas (version 3.2) - A system to support the management of water resources, Modernisation of the supervision and management of the water resource system of Athens, Report 24, 142 pages, Department of Water Resources, Hydraulic and Maritime Engineering - National Technical University of Athens, Athens, January 2004. Rozos, E., and D. Koutsoyiannis, Modelling a karstic aquifer with a mixed flow equation, 3nd General Assembly of the European Geosciences Union, Geophysical Research Abstracts, Vol. 8, Vienna, 03970, European Geosciences Union, 2006. Rozos, E., and D. Koutsoyiannis, A multicell karstic aquifer model with alternative flow equations, Journal of Hydrology, 2006. Rozos, E., and D. Koutsoyiannis, Application of the Integrated Finite Difference Method in groundwater flow, 2nd General Assembly of the European Geosciences Union, Geophysical Research Abstracts, Vol. 7, Vienna, 00579, European Geosciences Union, 2005. Managing water supply resources in karstic environment 23
Water basin model Digraph representation Virtual inflows River nodes Available GW Water demand Water pumping Simplex method is used to minimize the cost function. Managing water supply resources in karstic environment 24
Modelling the hydrosystem Groundwater model Use of an alternative flow equation was proved advantageous in simulation of water level fluctuation but the accuracy in calculations of fluxes was not improved. Q = C ( y D )α i 0.5 C: generalised conductivity [L3 T-1]. α: constant between 1 and 2. i: hydraulic gradient when y>d, slope when y D. Managing water supply resources in karstic environment 25
Results Herkynas Sim. Herkynas Obs. Oct-93 Oct-92 Oct-91 Oct-90 Oct-89 Oct-88 Oct-93 Oct-92 Oct-91 Oct-90 Oct-89 Oct-88 Managing water supply resources in karstic environment 26 Oct-87 Oct-87 Oct-86 Oct-86 Oct-85 Oct-85 Oct-84 Oct-84 2 1.5 1 m 3 /s 0.5 0 6 4 2 Melas Sim. Melas Obs. m 3 /s 0