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Hydrological Information System, Basic Tool in Water Management and Decision Making
Dr. Eram Artinyan, Dr. Dobri Dimitrov
;
National Institute of Meteorology & Hydrology, Sofia
Abstract
The design, set-up and operation of water related information and forecasting systems is of primary importance for the river basin management. The issue is especially valid for the basins shared by two or more countries, as mentioned in the EU Water Framework Directive. The paper deals with the Bulgarian experience in design, setting up and operating of some Information/Forecasting Systems at different Bulgarian river basins as follows:
Modeling and forecast of the Maritza river flow and river basin water and energy budget; the system consists of coupled surface scheme and a distributed hydrological model. It can be provided with historical, real time and forecast input meteorological data. The system is set-up for a large region in Bulgaria – about 34000 km2.
Struma/Strymonas Flood forecasting and warning system; this is Bulgarian – Greek research project targeting detailed investigation on flood formation and flood forecasting due to heavy rainfall phenomena as well as mixed rainfall – snowmelt phenomena. The project includes also installation and operating a system of automatic telemetric hydro-meteorological observation stations. Warning system set-up and operation will follow the research project to ensure better management and safety operation of the Kerkini Lake.
Short-range forecasting of some mountain reservoirs daily inflow; the system is serving the peak energy production using water accumulated at the Southwest part of the Maritza river basin. The system is in operation since late 2000 and uses coupled meteorological-hydrological forecasting models. The use of Limited Area High Resolution meteorological forecasting makes possible two days lead time of the hydrological forecast.
Iskar and Yantra River flows real time monitoring; this project covers two main Danube basin rivers in Bulgaria as a part of the cooperation between Romania and Bulgaria in the field of hydrology.
System for automatic hydro-meteorological data processing, archiving and presentation via Internet/Intranet: It covers mostly the conventional hydro-meteorological data from the Bulgarian territory and presents data in the NIMH intranet environment. Hydro-meteorological data are stored in a database server and made accessible through a web server. This system presents the data in tabular, graphical and mapped views. It was developed in the frame of the Med-Hycos and WOISYDES projects.
Keywords: Hydrology, forecasting, modeling, hydro-meteorological database
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Introduction
River basin management is a complex issue comprising variety of tasks and activities of different spatial and temporal scale. Information and forecasting systems are serving the short-term tasks of the river basin management, providing timely information about the development of the phenomena, facilitating water management and decision-making. The tasks become much more complex, when the trans-boundary issue is concerned, because of the necessity to consider in addition different legislation of the countries sharing the basin, different information polices and networks, culture and others.
1. Modeling and forecast of the Maritza river flow and of the river basin water and energy budget.
1.1. Description of the region
The region under consideration takes one-third part of the territory of Bulgaria – 34000 km2. It covers the central part of South Bulgaria, between the chain of Stara Planina Mountain and the state borders with Greece and Turkey at the south (Figure 1). The climate is continental to Mediterranean in the valleys depending on the dominant atmospheric circulation. It has pronounced altitude variability as the elevation is going from 50 m up to 2925 m at the pick of Mussala in Rila Mountain.
Figure 1: Map of the Maritza, Arda and Tundja River basins in Bulgaria
1.2. Objectives of the project
1.2.1. Real time monitoring of the natural water balance components and river flow forecast at predefined locations
· One to two days river flow forecast for the most endangered locations.
· To provide real time diagnosis of the river flow over a large region of the country.
· To evaluate the snow height and snow water content in real time
· Soil moisture evaluation for hydrological and agronomical purposes
1.2.2. Real time monitoring of reservoirs and channels water balance, and of water table level
· To analyze and predict reservoirs water inflow in order to help the decisions of water supply authorities
· Long term forecast of the underground water level and low-level river flow in order to prevent the shortage of water for irrigation and water supply.
1.3. Short description of the models used
1.3.1. High precision short-range numerical weather prediction model – ALADIN
Aladin short-range NWP model has been operating at the NIMH since May 1999. The numerical weather prediction model ALADIN (m.meteo.fr/aladin/) - has been used as operational model in Bulgaria since June 1999. The weather forecast for 48 hours over the Balkan Peninsula is computed twice a day using as initial conditions the predictions for 12 and 00 UTC of the French global model ARPEGE (Action de Recherche Petite Echelle Grande Echelle). The horizontal resolution of ALADIN is approximately 12 km, with 31 levels vertically. The model is widely used in Europe.
1.3.2. Land Surface Scheme – ISBA (Interface Soil Atmosphere Biosphere)
The ISBA surface scheme was developed for the climate, mesoscale and prediction atmospheric models used at Météo-France (m.meteo.fr/mc2/). It aims to represent the main surface processes in a relatively simple way: it solves one energy budget for the soil and vegetation continuum, and uses the force-restore method (Deardorff, 1978) to compute energy and water transfers in the soil. Evapotranspiration is computed through four components: interception by the foliage, bare soil evaporation, transpiration of the vegetation (with a stress function computed using the method proposed by Jarvis (1976) and sublimation of the snowpack. Two fluxes of water in the soil are computed: a surface runoff (RO) and drainage (D) (Figure 2). ISBA was coupled with the distributed hydrological model Modcou (Habets et al. 1999a, 1999b).
Figure 2: ISBA land surface scheme coupled with MODCOU macroscale hydrological model.
1.3.3. Distributed regional scale hydrological and hydro-geological model – Modcou
The macro-scale hydrological model MODCOU was used in several applications (Ledoux et al., 1989). MODCOU takes into account a surface and the underground layers. The surface routing network is computed from the topography, using a geographical information system (Golaz, 1995). The surface and underground domains are divided into grid cells of size 1, 2, and 4 km. The transfer between two grid cells is estimated by using the topography. The surface runoff computed by ISBA is routed to the river network (Figure 3) and then to the gauging stations using isochronous zones with a daily time step. The drainage computed from ISBA contributes to the evolution of the groundwater table, which evolves according to the diffusivity equation. The exchanges of water between the groundwater table and the river are computed according to simple relations (Ledoux, 1980). At the end, the flows from the surface layer and from the groundwater table form the riverflow at the gauging stations.
Figure 3: River network (blue) and area with existing water table (red). Gauging stations are shown with green squares.
1.4. Achieved project objectives
1.4.1. Analysis of the project feasibility
The overall analysis has shown that except the precipitation field estimation, which contains the higher error, all other fields could be used without special transformation. To correct the effect of the precipitation field on the water balance the measured precipitations could be used through sequential update of the soil moisture and other ISBA variables with that ones computed by using measured precipitations.
1.4.2. Automated field preparation
For the implementation of the two dimensional surface scheme and the distributed hydrological and hydro-geological model two-dimensional fields of meteorological variables are needed. In this case, most of them come from the ALADIN HRM but the precipitation field being the most critical is also computed on the base of near real time measurements. The real time processing of all the required fields has to be automated in order to supply the models with the needed input information.
1.4.3. Adaptation of ISBA-MODCOU coupled system for using Aladin precipitation fields
The use of Aladin precipitations only was expected to produce largely overestimated runoff, caused by the overestimated precipitation. That is because the initial conditions (soil moisture, soil temperature, snow density and height) had to be corrected after one or two days of surface scheme integration. The values for the re-initialization were taken from another ISBA integration having a delay of one or two daily steps (Noilhan, 2002), which was using measured precipitations instead of Aladin outputs.
1.5. Conclusion
· High resolution, short-range outputs from Aladin model can be used for the purpose of hydrologic modeling.
· For the forecast use, it is not possible to avoid inclusion of real and near-real time measured precipitations.
· The update of the ISBA land surface scheme variables (soil moisture, soil temperature, snow height and density etc.) have to be made at the shortest possible intervals, which is driven by the availability of new real time 2D precipitation fields.
2. Struma / Strymonas Flood Forecasting and Warning System
Struma is a mountain river flowing from North to South, from Bulgaria through Greece up to the Aegean Sea. It generates flush floods of snowmelt – rainfall type mainly in the late spring. Following the strong demand of Greece a project was started aiming to build the basis of a flood warning system, which should facilitate reservoir management downstream Bulgarian border, allow secure handling of the floods in Greek territory and generally decrease the flood hazard. The activities planed include installation of automatic telemetric hydro-meteorological observation network, review of the results of relevant projects, analysis of historical hydro-meteorological data, design and calibration of flood forecasting models, prove the possibility to issue flood warnings with certain lead-time and accuracy.
2.1. Introduction
Struma is collecting waters from four countries (Yugoslavia, Bulgaria, Macedonia and Greece), flowing from North to South up to the Aegean Sea. Considerable part of the river basin is situated in northwest Bulgaria (fig. 4.), having an area of more than 10000 km2 and average elevation about 900 m a.s.l. It is a mountain basin with steep slopes and relatively small concentration time, generating flush floods of snowmelt – rainfall type mainly in the late spring. Flood warnings are needed generally for the Greek lowlands to facilitate reservoir management downstream, allow secure handling of the floods in Greek territory and generally decrease the flood hazard.
Some real steps in organizing flood forecasting/warning system for the Struma river basin started in early 1990, when project briefs prepared by one of authors of this paper were presented to the Greek side. The WMO expert Dr. Alesh Svoboda during his advisory mission in 1992 prepared a project document related to flood forecasting for the Bulgarian-Greek border basins of Mesta and Struma, calling for UNDP support. The AUA Greek experts Prof. Karakatsoulis and Dr. Mimidis prepared in 1990 project proposal for Struma/Strymonas Flood Warning System. As a result the joint Bulgarian-Greek Intereg II – Phare CBC Committee found the problem as important one and gave start to research activities to be implemented by Bulgaria and Greece, which should prove the possibility to issue flood forecasts and warnings with acceptable for the practice lead-time and accuracy. For that purpose, the Bulgarian Phare CBC Program organized an international tender (project BG9803-030202) for delivery and installation of equipment for the Struma Flood Warning and Forecasting System in late 1999. The Greek company ScientAct SA was selected and successfully installed the equipment in early 2001 with the assistance of the National Institute of Meteorology and Hydrology, which is beneficiary of the project.
It should also be noted that the development of the WMO Med-Hycos project significantly facilitated the above one providing guidance, practices and the first automatic telemetric station in the basin (Figure 4).
The present paper is giving information on the activities of the side in the design and establishment of the telemetric hydro-meteorological observation network, analysis of historical hydro-meteorological data, design of hydrological forecasting model, first practical results, etc.
Figure 4: Telemetric observation network
2.2. First Results
The first results achieved by the Bulgarian team include:
· The telemetric observation network set-up and the operational data collection system. The system started functioning and collecting hourly averages of all the observed hydrological and meteorological parameters in January 2001;
· Analysis of relevant historical data set was completed. It includes review of 30 years series of daily averages of discharges, daily precipitation totals, snow heights, air temperature daily means and maximums observed at certain stations in the region. Different type of descriptive information, important for the design and calibration was also collected. That is valid for the hydrographic characteristics of the basin, information about the major soil classes in the basin, major anthropogenic impacts of the hydrological regime, etc. Examples of the work carried out in that direction are presented below. Separately the pluviograph data (rainfall intensity – Figure 8) were processed, which are unfortunately available for a few stations situated in the lowland and working only during the warm season. Relevant single flood waves (Figure 7) (using hourly discharges from limnigraph records) were analyzed as well, to determine more precisely the concentration time and flood peak discharge. The most important result here is that the southern parts of the basin usually start working first, due to the intensive snowmelts and rainfalls, caused by Mediterranean cyclones moving from South to North.
Figure 5: Struma river basin hydrographic curve
Figure 6: Struma river basin longitudinal profile
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Figure 7: Single flood wave analysis (hourly)
Figure 8: Rainfall intensity/duration curves
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· The first modeling was elaborated (Sosedko et al, 1990; Dimitrov, 2001). It is not practical to relay on the telemetric data as an input for the hydrological forecasting model because of the short concentration time (for some flood events less than 24 hours). Two days ahead meteorological forecast is used as first approximation of the precipitation and air temperature fields. Experiments were made with two types of simulation models using daily values: the Ukrainian SNEG2 (Sosedko et al, 1992; Dimitrov and Stanev, 1994); the Norwegian version of HBV (Stanev and Saelthun, 1993, 1994). Example of the results is presented below (fig. 10).
· It is foreseen that the real time rainfall/snowfall telemetric data will not be used directly as an input for the hydrological forecasting model. Meteosat satellite data and elevation gradients will be used for the spatial analysis of the precipitation fields. The analysis of the historical data set shows that the density of the observation network is not sufficient because of the mountain landscape conditions.