A TERRITORIAL INFORMATION SYSTEM FOR PLANNING AND
MANAGEMENT OF COMPLEX ARTIFICIAL DRAINAGE NETWORKS

Department of Hydraulic, Maritime and Geotechnical Engineering,

University of Padova

35131 Padova - via Loredan, 20 - Italy

tel. +39 049 8275432 fax +39 049 8275446

E-mail: bixiov@tin.it

 

 

Abstract: The land reclamation drainage network of the Veneto Region in north-eastern Italy is one of the most complex artificial drainage networks in terms of density of the channels and the man-made flow-control and monitoring installations. In order to provide a useful aid for the planning and management of measures in this area, a Territorial Information System has been developed specifically designed for the particular case of artificial networks, that frequently entail the building of new channels and installations, which must be included in the system with relative ease and without disrupting the architecture of the codified network. The above-mentioned System, which comprises approximately 16’000 km of channels and 5’000 installations, mainly pumping stations and flow-control and monitoring equipment, is expected to be particularly useful as a support for decision-making in a context in which the land-improvement network must not only fulfill its traditional function as a defense against flooding, but must also perform more complex functions, such as improving runoff water quality by means of suitable channel and installation management methods and innovative design conditions.

Keywords: management of drainage networks, land reclamation, territorial information system, geographical information system.

The proper programming of measures for complex drainage networks relies on their characterization in the framework of a Territorial Information System capable of describing their functions and establishing the effects of any changes in management policies by means of suitable simulations.

The fine-adjustment of such a system is particularly essential when, alongside the traditional hydraulic function of disposing of flood water, it also becomes necessary to use the networks for other purposes, such as to improve runoff water quality.

The development of an adequate Territorial Information System can prove complex, especially in the case of artificial drainage networks in which changes are frequently introduced, new channels are built and new plants are installed, all of which must be input into the system without interfering with its previous architecture.

A system of this kind has been fine-adjusted for the drainage network of the Veneto lowland area, which is unquestionably one of the most complex in terms of extension and density of channels and flow-control and monitoring installations.

This network, which is subdivided into 20 drainage districts, each managed by a Land Reclamation Consortium (Figure 1), extends over an area of approximately 1’184’000 hectares, 187’000 of which lies below mean sea level, 332’000 are mechanically drained and 95’000 are alternately mechanically drained.

Fig. 1  Drainage districts of the Veneto Region involved in the study and their corresponding surface areas.

2  THE STRUCTURE OF THE TERRITORIAL INFORMATION SYSTEM

A Territorial Information System represents a fundamental tool for managing and programming measures that a territorial organization such as the Land Reclamation Consortium is required to implement.

Within the system, data of various kinds can be organized and integrated, alongside programs specifically designed for their analysis and processing. The result is a somewhat complex structure, composed of the following main components: the information and data needed to define and deal with the problems to which the system is tailored; the management functions of these information, e.g. aggregations, updating, research and consulting; the programs specializing in processing the information in a spatial and temporal sense, depending on the purposes for which the system has been conceived; the function of representing the information that has been input or derived from the processing operations.

The Territorial Information System is based on a GIS (Geographical Information System), which has the following particular features: the opportunity to manage large amounts of spatially-referenced data and tables of attributes referring to them; the availability of analytical methods that deal specifically with the geographical component of the data, e.g. the automatic topological construction of the representation, the superimposing of themes and areas, the network analysis, the application of spatial models; the organized handling and feedback of large quantities of data, in both vectorial and raster format.

The GIS consequently enables the creation of an environment in which all the details describing the territory can be placed in relation to each other so as to generate further information. Hence the considerable benefits that the GIS offers to the Territorial Information System, i.e. the assessment of interactions between data sets, the prediction in real time of the influence and impact of any changes being planned, support for decision-making processes, the optimized management of the territory and of any activities that are performed in the area.

The description of the physical entity representing the context of the activities of the Land Reclamation Consortium, such as the hydrographic basins, channels and pumping stations, is implemented in the abstract form of area, stretch or arc, and node; the connection between these entities is guaranteed by a common code that enables a shift from one to the other type of information on the basis of their correlations (Figure 2).

Fig. 2  Example of the codification of nodes and stretches.

The nodes identify any geographically-referenced point of information that has a particular significance from the physical point of view, for example: the source or origin of a water course; the confluence of two or more water courses; any hydraulic structures such as siphons, flow-control apparatus, pumping stations, check gates, outlet works, side spillways; stations for measuring water quality, rainfall, temperature, air humidity, solar radiation, water level and flow rate.

The nodes have been unequivocally codified by attributing to each of them a number composed of 7 digits: the first 2 represent the code number identifying the Land Reclamation Consortium, and therefore identify the district to which the node belongs; the other 5 digits characterize the number of the node within the Land Reclamation Consortium. This number is always sufficient to identify all the nodes and, at the same time, it poses no hindrance to the introduction of new elements for a further definition of the drainage networks.

The set composed by the Land Reclamation Consortium code plus the node code represents a single code. Each node has been associated with an information file, which can be implemented with or without the addition of descriptive information.

The stretch coincides with a sequence of lines that joins two nodes; it corresponds to a stretch of water course and is identified unequivocally by a code comprising 10 digits, the first 5 of which are the same as the code of the upstream node, the other 5 for the code of the downstream node. A channel thus corresponds to the set, starting from upstream and progressing downstream, of the one or more stretches that comprise it: it is identified again by a figure of 10 digits, comprising the codes for the upstream and downstream nodes, in addition to 2 digits for identifying the district in which the channel is situated.

The fundamental area entity is the hydrographic basin, which can be composed of various orders of sub-basin.

The basin entities are distinguished by a basin code and, where applicable, by a sub-basin code, which is also included in the channel files, so that the passage between a channel and the basin into which it flows is immediately clear.

The hydrographic basin has been associated with a suitably-structured information file.

3  THE HYDROGRAPHIC AND STRUCTURAL ELEMENTS IMPLEMENTED

The research was carried out with reference to the 20 drainage districts of the Veneto Region; to each of these districts was attributed an identification code, which is consistent with the one attributed by the Veneto Regional Authority at the time of their establishment.

Table 1  Length of the hydrographic network, number of nodes for identifying the stretches of water course and number of installations.

The geographical data were implemented using the elements on the Regional Technical Map, on a scale of 1:10,000, suitably raster-scanned and geographically-referenced, and thus on a scale of considerable detail for establishing the course of the channels and the position and functions of the various drainage plants. The raster-scanned database provided with all the needed cartographic support from the beginning of the study, since the numerical format of the above-mentioned map was not available for the whole Region.

The installations belonging to each Land Reclamation Consortium were described by means of suitably designed files, completed on the strength of known data and subsequently integrated with further information and updates.

The number of nodes for identifying the stretches forming the network and the flow-control and monitoring installations considered are illustrated in Table 1.

This table gives an idea, first of all, of the considerable extension (16,431 km) and density (1.38 km/km2) of the drainage network.

The large number of nodes that had to be input to describe the network, amounting to approximately one node every 0.89 km, bears witness to its complexity and the degree of detail of the information that proved necessary in order to represent it.

In this context, the number of installations included in the Territorial Information System is remarkable, amounting to 5,387, mainly composed of pumping stations, check gates, flow-control and monitoring apparatus.

There are many channels of considerable size, and installations of major importance, particularly pumping stations, which have been built on them. In total there are 316 pumping stations, with a pumping capacity of approximately 1,400 m³/s.

The elements acquired on the structure of the drainage network and the corresponding installations contribute a good deal towards a better understanding of the relationships between hydrography and environment. The proposed Territorial Information System enables this information to be processed within the geographical context to which it belongs, even in an administrative sense, facilitating the immediate identification of the number and features of the manifolds falling within a given municipality or province, and thus establishing the possible relations between them and the activities to be programmed in the territory.

Fig. 3  View of a pumping station and example of some of the data implemented

Similarly, the associated files enable a detailed description of the installations, from which many kinds of information, such as water levels, types of equipment installed, or runoff flow rates can be extracted as necessary.

The information of an alphanumerical nature can also be integrated with further details in graphic form, progressively implemented according to need and availability. For instance, Figure 3 shows a picture and some of the information implemented for a pumping station, Figure 4 shows the same for a check-gate.

The geographical aggregations processed for each basin or drainage district can be composed to obtain data of hydraulic and functional nature relating to any geographical context: for example, within the area considered in the study, the subset comprising the basins discharging into the Venetian Lagoon is of particular interest (eight of the twenty drainage districts involved in the study include areas, with an overall surface area of approximately 200,000 hectares, crossed by water courses that are more or less important tributaries of the Venetian Lagoon).

Fig. 4  View of a check gate and example of some of the data implemented.

Of course, the potential applications of the Territorial Information System are numerous.

First of all, it is worth mentioning its uses in a design context and, more in general, in the hydrological and hydraulic modeling sectors, which need the support of the data provided by the system about the structure of the drainage networks and the operation of the flow-control installations.

In addition, the Territorial Information System can prove particularly valuable when it is used in relation to the development of environmental activities, characteristic of the work of the Land Reclamation Consortium alongside the traditional hydraulic purpose. In this context, it is particularly worth mentioning the drainage network management methods designed to reduce the concentration of pollutants in the runoff water.

In the Venetian Lagoon watershed, for instance, these techniques are being proposed mainly to reduce the quantities of nutrients (e.g. nitrogen and phosphorus) in the drainage networks flowing into the lagoon by means of various procedures based essentially on increasing the water retention time in the channels (Bixio, 2000).

To be implemented properly, the programming of such measures and management techniques must be part of a global and detailed understanding of the territory that only a Territorial Information System of the kind discussed here can provide.

Bixio, V.: “Water quality improvement in the drainage networks flowing in the Venetian Lagoon”. Proceedings of the International Workshop on Development and management of flood plains and wetlands (IWF 2000), 5-8 september 2000, Beijing, China, pp. 107-116.