Abstract The paper summarizes a hydrologkal study of the Po. River catchment area within the framework of a water resources planning study for the next two ...
The Hydrologkal Basis for Water Resources Management (Proceedings of the Beijing Symposium, October 1990). IAHS Publ. no. 197,1990.
Water resources planning of the River Po basin: a surface and groundwater hydrology study S. ARTTNA, M. FERRARESL E. TODINI & F. ZOCCOLI* Institute of Hydraulic Construction, Engineering Department, University of Bologna, Viale Risorgimento 2,1-40136 Bologna, Italy
Abstract The paper summarizes a hydrologkal study of the Po River catchment area within the framework of a water resources planning study for the next two decades. The analysis of hydrologkal data and their treatment, together with the establishment of an efficient data bank is presented as a prerequisite for the regionalization of the hydrologkal information. The calibration of surface and subsurface water flow models is then introduced in order to allow for the verification of congruence of historical data and for the analysis of compatibility and risk of future development plans. Planification des ressources en eau du bassin du Pô: étude d'hydrologie de surface et d'hydrologie souterraine Résumé L'article résume une étude hydrologique du bassin du Pô, dans le cadre de la programmation des ressources en eau des deux prochaines décennies. On présente ici l'analyse des données hydrologiques et leur traitement, avec la mise en oeuvre d'une banque de données, étape préliminaire pour la régionalisation de l'information hydrologique. En outre, on a procédé à la calibration des modèles de simulation du mouvement des eaux de surface et souterraines pour vérifier la congruence des données historiques, la compatibilité et les risques liés aux plans futurs de développement. INTRODUCTION In this paper the hydrologkal aspects of a water resources planning study for the Po River are described, in order to emphasize the problems arising in a large scale project, together with the aims and perspective which can reasonably be expected. The optimal allocation of water resources in the River Po basin represents a management problem of great concern, owing to the size of its catchment area and the importance of the related economical and social interests. The Po basin, approximately 70 000 km2, covers most of northern Italy, a little less than one fourth of the entire national territory (Fig. 1). Over 18 •Deceased.
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Fig. 1 The River Po basin and its plain area (within the dotted line). million inhabitants live in this area, producing more than 40% of the total national gross product. The Po valley, about 28 000 km2, has an extensive agricultural development, well supported by the water availability. The size of the problem at hand can better be appreciated by considering Table 1, which shows the main contributions, expressed in km3, to the overall water balance of the plain for the year 1981. The plain is the area on which the interest for water resources planning is focussed, and represents one of the two regions into which the whole River Po catchment has been subdivided, the second being the mountain areas. The latter cover the external part of the Po basin and are drained by rivers coming from the Alps and the Appennines, which are mostly impervious and where aquifers usable for exploitation are virtually absent. The plain covers the remaining central portion of the Po catchment, ranging from 150 m of altitude to the Adriatic Sea (Fig. 1). In order to determine optimal management policies, a preliminary identification of the River Po hydrological system is required, together with an analysis of the interconnected agricultural, industrial, municipal and social systems. For this purpose, the Canale Emiliano Romagnolo, a land reclamation agency of the Po valley, was commissioned by the Italian Ministry of Agriculture and Forestry to lead a multidisciplinary water planning study, which is outlined in Ministry of Agriculture (1984). The present paper deals only with the hydrological system and closely related aspects of the study.
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Table 1 Main contributions to the 1981 water balance in the Po valley (area = 28 000 km2) INFLOWS
km*
Surface discharges from mountain basins Precipitation Groundwater supply from mountain basins Total inflow
34.7 21.7 2.4 58.8
OUTFLOWS
km3
Po discharge to the sea Evapotranspiration Artificial drainage Total outflow
42.6 15.6 0.6 58.8
INTERNAL EXCHANGES Abstractions for agriculture Abstractions for domestic use Abstractions for industry
19.0 3.9 3.4
HISTORICAL DATA ANALYSIS AND MANAGEMENT The historical data used in this study relate to the years 1951-1981 and were mainly provided by the Italian Hydrographie Service. Additional information was given by the Ministry of Aeronautics and by agricultural and hydropower agencies. The number of measurement stations over the entire catchment area is: Rainfall stations 1123 Temperature stations 217 Water levels or discharge stations131 Wind stations 45 Humidity stations 18 Solar radiation stations 6 Water table wells 1080 The first problem to be solved was obviously the storage of this huge amount of information, sampled at monthly intervals, in the most effective and efficient way. A hydrologie data bank was set up, following the guidelines of Component. GO6.3.01 of HOMS (Hydrological Operational Multipurpose Subprogrammes) (WMO, 1974) where the data were introduced in a direct access mode, on a relational basis, by station and year, together with "catchment files" describing the relevant stations for each basin and providing the correct addresses for the retrieval of the corresponding necessary information.
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Another problem, a major one, consisted of the homogeneity analysis of the data and reconstruction of the missing observations. As far as the first aspect is concerned, techniques based upon single linkage cluster analysis were used to discard the inconsistent stations, while autocorrelation functions and power spectra were used to ascertain the natural behaviour of recorded complete time series. According to the nature of each type of the collected data, different approaches were used in order to fill the gaps and compute the areal averages. Principal component analysis was performed on those rainfall series which were complete (about 30% of the total); the missing observations were then reconstructed by regressing the incomplete series on the first 15 principal components, which explain more than 90% of the total variance of rain. Owing to the low spatial variability of temperature, these data series were completed by multiple linear regression on surrounding stations, after scaling the data to a common mean elevation, by means of a gradient of 6°C km"1. Thermal gradients ranging from 4.7 to 6.4°C km"1 were suggested by the existing literature for various basins in northern Italy; the value chosen was the most appropriate as an average over the entire region of interest. By means of the temperature information, the potential évapotranspiration was computed according to the Thornthwaite equation (Doorenbos & Pruitt, 1974) and stored in the data bank. The évapotranspiration estimates were then rescaled by comparison with the values computed through the Penman energy budget equation for the stations where wind speed, humidity and solar radiation were available. Finally, the areal averages of rain and temperature were estimated using an original minimum variance method, which compared favourably with the Gandin (Gandin, 1972) and Kriging techniques (Matheron, 1970). A summary of all the operations performed on the hydrological data is given in Fig. 2.
SURFACE HYDROLOGY In order to simulate its hydrological phenomena, the River Po catchment was subdivided into two regions: the mountain areas (about 42 000 km2) and the plain (about 28 000 km2). The mountain areas The monthly runoff contribution from the mountain catchment had to be reconstructed at all the sections where the rivers enter the plain. In a first phase, the runoff data from 75 hydrometric stations with more than six years of continuous measurement were utilized to compute the mean annual runoff, Q, which was successively regionalized by means of regression equations of the type:
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COMPLETENESS
RAINFALL
DATA
A N A L Y S I S ON HISTORICAL
DATA
COMPLETENESS ANALYSIS HISTORICAL FROM
ON DATA
DIFFERENT
SOURCES
C A L I B R A T I O N OF MEAN
RECONSTRUCTION 0 ?
IDENTIFICATION
ANNUAL RUNOFF
MEAN RUNOFF AT RELEVANT
OF CA"
