CCCEEENNNTTTRRROOO EEEUUURRROOO---MMMEEEDDDIIITTTEEERRRRRRAAANNNEEEOOO PPPEEERRR III CCCAAAMMBBBIIIAAAMMMEEENNNTTTIII CCCLLLIIIMMMAAATTTIIICCCIII
ISC – Divisione Impatti sul Suolo e sulle Coste
s s t t FFiinnaall ddooccuummeenntt oonn tthhee sseeccoonndd r r o o yyeeaarr ffiirrsstt aaccttiivviittyy:: ““DDEEMM p p ggeenneerraattiioonn aanndd iinntteerrffaaccee wwiitthh tthhee e e 22DD nnuummeerriiccaall mmooddeell ooff fflloooodd R R
pprrooppaaggaattiioonn”” l l a a c c * i Prof. Francesco Macchione i
n * n Ing. Pierfranco Costabile h h Ing. Carmelina Costanzo* c c e e * LAMPIT (LAboratorio di Modellistica numerica per la Protezione Idraulica del Territorio) – Dipartimento di Difesa del Suolo – Università della Calabria T T
Centro Euro-Mediterraneo per i Cambiamenti Climatici www.cmcc.it February 2008 ■ TR
Final Document related to the second year first activity: “DEM generation and interface with the 2D numerical model of flood propagation”
Abstract
This report represents the final document related to the second year first activity whose title is: “DEM generation and interface with the 2D numerical model of flood propagation”. The purpose of the collaboration between LAMPIT (University of Calabria) and CMCC is to develop an hydrometeorological chains in order to obtain a reliable tool in the context of flood evolution prediction able to provide quantitative information of practical importance within the civil protection activities. The LAMPIT contribution to the project concerns the mathematical description of both the generation and propagation of flood events at reach scale. The work here presented, carried out in close cooperation with dr. Pasquale Schiano and CIRA researchers (dr. Paola Mercogliano & dr. Gabriella Ceci), summarizes the activities related to both the DEM generation of the Tammaro basin and the evaluation of the possible effect of the Campolattaro dam on the flood event selected as case study.
Keywords: Hydrometeorological chains, Flood propagation
JEL Classification:
Address for correspondence: Prof. Francesco Macchione Laboratorio LAMPIT Dipartimento di Difesa del Suolo – Università della Calabria Ponte P.Bucci – Cubo 42/B 87036, Rende (CS) . E-mail: [email protected]
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DEM GENERATION OF TAMMARO BASIN
The suitable generation of the Digital Elevation Model (DEM), in part started at the end of the first year, represents a significant working phase of the second year first activity. The morphological description of the Tammaro basin have been carried out by means of ArcGis software, as stated in the second technical report of the first year. A lot of problems have been encountered during the DEM generation of Tammaro basin mainly due to the cartographic original data whose quality was sometimes not clear at all; moreover, some difficulties have been arisen dealing with the representation of particular elements and structures within the basin. Anyway, in the first step the attention has been focused on the geographic data acquisition; in particular the topographic data, in scale 1:5000, provided by CIRA on September 2007 have been used; the basin has been thus discretised according to a 5 m size square grid. The second step has been concerned with the transformation of the original cartographic data in a suitable format that can be managed by ArcGis. Starting from the original file in “.dwg” format, the altimetrical data (spot elevations and contour lines) have been extracted and vectorialized (obtaining the shape file) and then sorted within a geodatabase (that is a specific tool used by ArcGis) which allows a better data management. The shape files have been then digitalized by means of a ArcGis function, called Topo to Raster, that is a suitable interpolation method to the generation of hydrologically correct DEM. The previous technique, based on the works of Hutchinson (1988), allows to obtain a well-connected drainage catchment and a correct representation of the thalwegs of rivers.
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Figure 1 - Tammaro basin at Paduli station
(a)
(b)
Figure 2 Details of the basin near the Campolattaro dam (a) and at Paduli measuring station (b)
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Moreover, during the digitalization works, particular attention has been given to the edges management for each cartographic map sheets in order to avoid an incorrect interpolation near the edges themselves. In summary, by using particular tools within ArcGis, the following procedure has been used:
Characterization of the flow directions path for each cells; Location of the end section of the Tammaro basin ; Basin delimitation; Characterization of river network.
The vast amount of work carried out during this activity may be deduced by the analysis of the figures 1-2 where a 3D view of the Tammaro Basin, at the Paduli site, is shown. In the figure 3, the longitudinal profile of the Tammaro river is depicted while in the figures 4-7 some cross sections of the valley are presented.
Figure 3. Longitudinal profile of Tammaro River
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Figure 4. Tammaro river
Figure 5. Cross section 1
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Figure 6. Cross section 2
Figure 7 Cross section 3
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Figure 8. Cross section 4
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EVALUATION OF THE POSSIBLE EFFECTS INDUCED BY THE CAMPOLATTARO DAM ON THE FLOOD EVENT CHOSEN AS CASE STUDY
The last working phase have concerned with a number of analysis aimed at the evaluation of the effects induced by the presence of Campolattaro dam on both flood generation and propagation. In the figure 8, an orthophoto depicting the actual situation of the basin is shown while in the figures 9-11 some planning pictures together with a photograph took during the construction of the dam are shown. The presence of the Campolattaro dam, found out only during the activities related to DEM generation, clearly represents a further significant problem in the context of the validation of the hydro-meteorological chain applied to the above mentioned test case; on the other hand, the upstream basin of the Campolattaro dam covers about the 30% of the whole basin upstream Paduli site (figure 12). Both historical surveys and hydrological estimations have been thus carried out in order to assess whether the dam have played a significant role on the flood event chosen as case study. In this context the analysis has been organised according two steps. On one hand, an hydrological tool aimed at reproducing the flood wave observed at Paduli site has been used; in particular a rainfall-runoff study has been performed by means of a commercial software. On the other hand, the behaviour of the Campolattaro dam during the flood event of 5-6 March 2005 in the Campania Region has been inquired.
Figure 8 – An orthophoto of the Campolattaro dam showing the actual water storage.
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Figure 9 – Overall planimetry of the Campolattaro dam
Figure 10 – Overall view during the construction of the Campolattaro dam
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Figure 11 – Upstream view of the dam, typical cross section, longitudinal profiles of the bottom outlets
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Figura 12 - Sub-basin upstream the Campolattaro dam (in red)
RAINFALL-RUNOFF MODELLING
Significant effects may be induced by the presence of the Campollataro dam on the flood hydrograph due to the potential storage phenomenon. In order to analyse the above mentioned effect, a commercial hydrologic software has been used to reproduce the general features of the observed flood wave at Paduli station assuming the absence of the dam itself. In this context, starting from the total rainfall simulated by CIRA through the meteorological model, a rainfall-runoff modelling has been performed using HEC-HMS software. This code schematizes the basin as a number of subbasins connected by channels; in each subbasin, assumed as homogeneous from an hydrological point of view, the transformation of rainfall into runoff occurs. The flood waves computed for each sub- basin represent lateral discharges that propagate along the channels; the logical scheme is illustrated in the figure 13 where both the subbasins and channels are shown.
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Figure 13 – Conceptual scheme of the basin according HEC- HMS
Therefore the methodology used can be summarized as follows:
Characterization of the sub-basins assumed homogeneous from an hydrological point of view Computation of a rainfall value, constant in space but variable in time, for each sub- basin Rainfall-Runoff analysis within each sub-basin Hydraulic propagation along the channels
The extracted sub-basins have the following features:
MEAN OUTLET REACH SUB-BASIN AREA REACH SLOPE ALTITUDE ALTITUDE LENGHT
Km2 m a.s.l m a.s.l. Km m/m B1 275,5 658,79 294,63 43,50 0,02 B2 123,0 636,86 294,65 29,50 0,02 B3 58,0 611,87 284,71 20,90 0,03 B4 55,7 657,63 255,00 14,90 0,05 B5 5,2 356,95 284,48 3,90 0,04 B6 33,6 395,57 255,00 14,00 0,02 B7 118,7 420,86 124,59 29,30 0,03
Starting from the rainfall simulations made by CIRA through the meteorological model referred to a 7 km grid size, the further step has concerned with the computation of the
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rainfall data evolution that has been considered as a constant value within each sub-basin. By using the well-known methodology based on the Thiessen polygons, it was possible to identify the influence areas of each rain data and computing the mean rainfall values in the sub-basin through the isohyetal method (figure 14).
Figure 14 – Influence areas of each rainfall data
Then a rainfall-runoff computation has been performed. The basic idea of the rainfall- runoff modelling is to relate the discharge values to the net storm rain by means of a suitable transfer function: t qt()=−∫ p (τ ) gt (ττ ) d 0
where t is time, q is the discharge value, p is the net rain, g is the so called instantaneous unit hydrograph that is the basin response to an unitary and instantaneous impulse. The simulation have been carried out using both the SCS-CN method to the evaluation of the net rain and the UH method to model the function g. According to SCS-CN model, the net rain p is computed as follows:
()RI− 2 p = a ()R − ISa +
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Where R is the volume of the precipitation, S is the maximum volume of retention, Ia is an initial retention of rainfall in the soil. The maximum volume of retention S depends on both type and use of soil globally included within the CN parameter defined as follows:
⎛⎞100 S = 254⎜⎟− 1 ⎝⎠CN
Where 0 LOAM LOAMY CLAY Figure 15 – Soil characterization within the Tammaro basin The flood wave, computed by means of the methodology above described, is shown in the figure 16 together with the observed hydrograph. The comparison highlights that the recession part of the hydrograph is underestimated. A number of investigation are actually in progress in order to collect data on the effective water level variations of the Campolattaro storage during the event of March 2005 in order to better quantify the effect of the storage capacity on the flood evolution. 15 Figure 16– Comparison between computed and observed hydrographs Historical survey The water storage capacity on Tammaro River is known as “Campolattaro dam” because the works are located at the bottom of Campolattaro town (located at 430 m above sea level) but a large part of artificial lake generated by the dam is placed in the Morcone area (683 m above the sea level). Some design features of the dam are shown in what follows: Maximum water surface level: 381.45 m s.m.m; Crest level: 387.40 m s.m.m.; Crest width: 9 m; Crest length: 820.6 m; Dam Height: 62.90 m; Maximum storage volume: 87.200.000 m3 Total volume: 125.000.000 m3 The works, carried out by Ferrocementi firm, started in the 1981 and finished in 1993. At the ending of the works in 1993, the problem concerning the management trust of the dam was pointed out because, in the meantime, the agency “Cassa per il Mezzogiorno“ has been abolished and the relative competences has been transferred to the Regional and National facilities. After lengthy institutional consultations, the Benevento provincial administration become the management trust with the cooperation of two agencies: “Ente per lo sviluppo dell’Irrigazione” e “Trasformazioni fondiarie in Puglia, Lucania e Irpinia”. In practice the previous agreements occurred on 20.10.1997. 16 However, another problem kept Tammaro dam from working until 29 April 2006: a significant landslide occurred on the right hillside of the dam. The competent authority interrupted the procedures concerning the experimental storage test of the dam since they considered more important to carry out safety measures of the site. Once finished the previous works, the Registro Italiano Dighe that has the superintendence of the dam, authorized the “first technical storage” on 29 april 2006. For further details one may refers to the following web page: http://www.campolattaro.eu/Pagine/Diga.asp. 17