Hydrogeological Map Monti Lessini

8/10/2019 Hydrogeological Map Monti Lessini

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CARTA IDROGEOLOGICA DEI MONTI LESSINI - HYDROGEOLOGICAL MAP OF LESSINI MOUNTAINS

HYDROGEOLOGICAL MAP OF LESSINI MOUNTAINS

1. GEOGRAPHICAL LOCATION

The Lessini Mountains are in the western part of the Venetian Fore-Alps (fig. 1) and develop over

an area of approximately 1500 km2. From an administrative point of view, they belong to the

provinces of Verona, Vicenza, and Trento. They are bordered by the Adige Valley to the West, by

the Leogra Valley to the East and N-E, while the Val dei Ronchi separates them from the Pasubio

Carega Group in the north-western sector. From a geographic point of view, they include the

western Lessini Mountains (from the Adige Valley to the Illasi Valley) and eastern Lessini

Mountains (from the Illasi Valley to the Leogra Valley).

In the territory of the Veneto Region, the Lessini Mountains are subdivided in the Lessini Veronesi

(fig. 2) and Lessini Vicentini, separated by the Mount Calvarina ridge (683 m a.s.l.) included

between the Alpone Valley (VR) and the Chiampo Valley (VI). The maximum altitude reached by

these mountains is 1865 m a.s.l. (with the Cima Trappola).

The Kater II project covers the area included between the Adige Valley and the Chiampo Valley,extending for an overall length of about 980 km2, mainly involving the territory of the province of

Verona and only partly that of Vicenza.

As explained in detail later, the western Lessini Mountains essentially consist of carbonate rocks,

whose role is particularly important in the development of karst phenomena, while the eastern

Lessini Mountains are prevalently made of volcanic rocks linked to the tertiary venetian

magmatism: here, the karst morphology is virtually unseen, while the territory is mainly modelled

by gravitational causes. In its turn, the tectonic pattern equally affects the evolution of surface

forms in both sectors.


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Figure 1: Geographical location of the Lessini Mountains

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Figure 2: A panoramic view of the Conca dei Parpari

2. CLIMATIC FEATURES

Generally speaking (SORBINI, 1993) the pluviometric regime in the area of the Lessini Mountains is

very similar to that of Fore-Alpine areas, though with a much lower average rain levels. The

variability of total rainfall approaches 22% and reaches 28% in the northern and higher sector of

the basin. On average, the permanence of snow on the ground varies from a few days at low

altitudes to 35 months at higher altitudes.

The graphs below show the rainfall values obtained by processing the data provided by ARPAV

regarding the sites in the Lessini territory where continuous measurements concerning the 1992 to

2005 period are available.

Figure 3: Annual rainfall in Fosse di S. Anna dAlfaedo

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Figure 4: Average monthly rainfall in Fosse di S. Anna dAlfaedo

The longest and most complete series of the area refers to the Fosse di S. Anna dAlfaedo station

(954 m a.s.l.), consisting in measurements taken in the 1961-1990 30-year period (figs. 3 and 4).The rainfall regime of this station seems to be slightly abnormal compared with the typical regime

of Fore-Alpine areas registered by the other stations (fig. 5). In fact, the most rainy month in Fosse

di S. Anna is August, followed by May and June, while the other pluviometric stations detected

more abundant rainfalls in autumn and, in the second place, in spring, except for the Illasi area,

where the second maximum is reached in the summer. All the other stations showed that the less

rainy month of the year is February.

Figure 5: Average monthly rainfall in the meteorological stations of Lessini Mountains

Comparing the annual values obtained by pluviometric stations with comparable data are

available (fig. 6), it comes out that the average annual rainfall ranges from 826 mm to 1413 mm.

The highest values are seen in the mountain areas, and secondarily in the areas at the western

(Dolc) and southern margins (Montecchia di Corsara) of the Lessini Mountain.

Figure 6: Average annual rainfall in the meteorological stations of Lessini Mountains

As far as temperatures are concerned, average annual values are established around 13 C in the

mid-low Lessini region, and around 9.3 C in San Bortolo.

Data regarding temperatures (1992-2005) show a thermal regime characterised by maximum

average values in the months of July and August, and minimum values in the months of January and

December (fig. 7).

Figure 7: Average maximum monthly temperature in the meteorological stations of Lessini Mountains

One anomalous finding is the value of average minimum temperatures in the months of January,

February and December in the Montecchia di Crosara station (fig. 8), which is placed at 50 m

above sea level, but in spite of this shows lower temperatures in these months even compared to the

San Bortolo station that lies at an altitude of 936 m. This anomaly, which may be attributed to local

thermal inversion phenomena, is also highlighted by the frequent presence of fog in the area.

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Figura 8: Average minimum monthly temperature in the meteorological stations of Lessini Mountains

3. GEOMORPHOLOGY

3.1

MorphologyFrom a morphological point of view, the Lessini Mountains complex consists of an inclined plateau

sloping SW for about 5. Its southern and central parts are deeply carved by a thick series of

parallel valleys generally positioned in NNE-SSW (to the West) and NNW-SSE (to the East)

directions. These valleys, which are called vaj or progno by the locals, are initially narrow,

but then widen up considerably as long as they proceed southward. Their rectilinear course shows

a clear tectonic influence: the Lessini valleys, in fact, are set on tectonic discontinuities.

The long and narrow ridges that lead off the wide northern plateau (fig. 9) plunge below fluvial-

alluvial areas when they reach the plain and then re-emerge locally in the form of low isolated

hills.

Figure 9: View from a ridge summit near Conca dei Parpari

The summit tableland of the Lessini Mountains extends for about 60 km2and is entirely covered

with grazing land.

The area examined (the central-western Lessini) may be in turn divided into different areas

depending on their altitude and different evolution of the local morphology: a basal strip, between the Adige riverbed and 900 m a.s.l., where valley incisions extend

upwards, until they become large hilly areas (fig. 10);

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an intermediate strip, between 900 and 1200 m a.s.l., characterised by narrow ridges and

narrow valleys (locally named vaj), with many scattered human settlements (fig. 11);

a summit strip or upper Lessini, between 1200 and 1800 m a.s.l., with extensive grazing

land from which impressive rocky peaks emerge. In the North, the surface slopes down

towards the Trentino Region, with marked slopes and steep cliffs. This area is the site that

presents the most interesting karst phenomena (fig. 12).

Figure 10: The wide valley-bottom of Vajo di Squaranto nearby Montorio

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Figure 11: The village of Lesi (Bosco Chiesanuova)

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Figure 12: Karst phenomena in the upper Vajo di Squaranto

3.2Karstification

The karst phenomenon has not given to the Lessini Mountains area the classic karstic features

(dolines, polje), even though the total absence of surface water already informs us about the

magnitude of the underground phenomenon. The hypogean forms are extensively and largely

spread, as proven by the 825 caves known until today, some of which are extremely important.

SAURO(1973) describes karstification in the Lessini Mountains both as fluvial karst, for the clear

predominance of river morphologies, and as tectonic karst, for the significant impact of tectonics

on the development of karst and, consequently, onto the entire landscape.

The role played in karstification and in the hydrogeological system of the Lessini Mountains by

overburden (landslide deposits, moraines, debris, eluvial and colluvial deposits) is very important,as it represents epikarst water reservoirs that are slowly released into the underlying karstfied

rocks.

Acting on the several rock formations of the area, karstification has developed different

morphologies that vary based on their lithology; for example, the so-called rock cities (fig. 13)

are a typical phenomenon of Rosso Ammonitico, while dells and dry valleys are more typically

found on Biancone, on Oolite di S. Vigilio and Calcari Grigi (figs. 14 and 15). Dolines are

prevalently formed by the contact between Biancone and the underlying jurassic limestones, while

rocks, which are more favourable to the development of caves, are Rosso Ammonitico, Oolite di S.

Vigilio and Calcari Grigi.

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Figure 13: The Rock City near Camposilvano (Velo Veronese)

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Figure 14: Dry valley (Conca dei Parpari)

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Figure 15: Small dolines on the floor of a dry valley (Branchetto Pass)

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The most common among hypogean forms are vertical development caves, such as, for example, the

Spluga della Preta (near the Corno dAquilio), a drop of 877 m to create the third deepest cave of

the Veneto Region and a space extent of 4518 m to give the fourth largest cave of Veneto.

In addition to Spluga della Preta, the main caves in the area examined are Spurga delle Cadene

(Dolc) and the Lesi Abyss (Bosco Chiesanuova), with space developments of 1200 m and 472 m,

respectively. More well-known karst morphologies are Covolo di Camposilvano (fig. 16), animposing 83 m deep collapse dolines, and the Veja Bridge, near S. Anna dAlfaedo, a hypogean

complex consisting of a natural rock bridge that represents the non-collapsed portion of the vault of

the initial chamber.

More spectacular typical karst forms of the Lessini Mountains can be admired in the Sphinx Valley,

in the vicinity of Camposilvano (fig. 17).

Figure 16: Covolo di Camposilvano

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Figure 17:Sphinx Valley, near Camposilvano

3.2.1 The Sphinx Valley

The Sphinx Valley area is recognised as a natural monument representing a karst landscape named

rock city (figs. 13 and 17). The evolution of karst erosion combined with other physical-chemical

crumbling processes have enlarged the pre-existing vertical discontinuities and karst fissures, thus

creating karren and corridors in Rosso Ammonitico layers. This generated special stone blocks,

either isolated or in groups, with typical parallelepipedon (fig. 18) or mushroom-like forms (fig.

19). The typical rock "mushrooms" have a "hat" of Rosso Ammonitico, that is more resistant to

erosion, and "stalk" of the oolitic calcarenite belonging to the S. Vigilio Group, with a greater

susceptibility to erosion.

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Figure 18: Rock city (Sphinx Valley Camposilvano)

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Figure 19: The Mushroom(Sphinx Valley Camposilvano)

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3.2.2 Covolo di Camposilvano

Covolo di Camposilvano (fig. 16) is the most interesting example of collapse doline found in the

Lessini Mountains. It is a spectacular and very peculiar karst cave generated by the collapse of a

great doline set on Biancone, Rosso Ammonitico and oolitic limestones of S. Vigilio Group. The

entrance of the cave is at an altitude of 1204 m, the global drop is 83 m, the diameter is 60 m and

the global development ranges for 130 m.Globally, the Covolo is a set of karst caves consisting of many rooms that form a complex system

originated by the karst processes connected with water circulation between layers.

The main cavern sometimes works as a trap for cold air: the considerable temperature difference

from external air may sometimes result in ice formations in spring, which may even last throughout

the year, or in the development of condensation mists.

Not far from the karst cave lies a small local museum (fig. 20) preserving interesting fossil remains

and pre-historic findings that have been found nearby, including both mineral and fossils, either

local or from other places. In particular, the Covolo area, which was already settled by humans in

the Neolithic age, is an important deposit of Quaternary fossils, with bone finds from holocenic

Cervus sp. and Bos taurus.

Figure 20: Shark vertebrae and ammonite fossils at the entrance into the Museum of Camposilvano

4 GEOLOGY

4.1

Stratigraphical successionThe Lessini Mountains mainly consist of carbonate sedimentary rocks dating back to the Mesozoic

and Tertiary periods. Cretaceous-Jurassic lithotypes crop out in the northern sector, while the

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southern sector is occupied by Eocene lithotypes. The lithology here (fig. 21) essentially consists of

dolomite rock, dolomitic limestone, limestone and marly limestone, but Eocene volcanic rock also

crops out, mainly in the Alpone Valley.

Here are the formations of the stratigraphic series of the Lessini Mountains: Dolomia Principale,

Calcari Grigi, Oolite di S. Vigilio, Rosso Ammonitico, Biancone, Scaglia Rossa, eocenic limestone.

Basaltic volcanic rocks (such as basalts, hyaloclastite and tuffs) crop out only in some parts of theterritory, prevalently in the eastern sector.

Figure 21: Lessini Mountains lithologies visible in the walls of a building

The most ancient formation is the Dolomia Principale, which consists of bioclastic calcarenites,

biomicrites, and stromatolites. The overall power of 900 m is almost entirely visible only on the

Adige and Ronchi valley slopes, while only the highest portion of the units emerges from the upper

Illasi Valley.

Jurassic units are represented by Calcari Grigi, Oolite di S. Vigilio and Rosso Ammonitico (fig.

22), with an overall 400450 m thickness. From a lithological point of view, oolitic calcarenites are

frequently found, together with biostromal limestones, lumachelle limestone, encrinitic calcarenites,

and marly flinty limestones, while the most recent terms are micritic limestones. These formations

make up the main frame of the Lessini ridges and form the slopes of the deeply-embedded, and often

vertically walled, valleys.

Rosso Ammonitico has peculiar morphological features: it generates both the summit frames of the

ridges, as well as the shelves along the slopes and the plateaus of the northern tableland.

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Figure 22: A quarry near Camposilvano, with Oolite di S. Vigilio (below) and Rosso Ammonitico (above)

Stratigraphically overlying jurassic terms are the Biancone and Scaglia Rossa formations, lower

and upper Cretaceous in age, respectively. They consist of thickly-stratified fine-grained limestones,

whose global thickness ranges from about 200 m in the western sector to over 400 m in the eastern

sector. They come in the form of wide strips, scarcely steep along the slopes and rounded ridges at

the top of the medium-high Lessini Mountains.

The top member of the Biancone, which corresponds to the Cenomanian (fig. 29), plays a

significant role for its important hydrogeological implications: they are thickly-stratified marly

limestones and bituminous marls, whose thickness ranges from 50 to 80 m in the area of the Lessini

Mountains. In particular, the passage to the Turonian is marked by 65130 cm of black and yellow

argillites and siltites. This formation is intensely fractured in the Lessini Mountains due to the

presence of many faults, and plays a considerably important role from a hydrogeological point of

view (see section 5).

Subsequently, during the Paleogene, basalt-like volcanic rock was laid in the Alpone-Agno graben

which took the form of small-grain, often stratified, breccias. The same magmatic cycle also

includes dyke bodies and eruption vents of breccia (necks), which intruded into sedimentary

formations all over the area of the Lessini Mountains (fig. 23).

Units of the Eocene (Scaglia Cinerea, Calcari Nummulitici and Marne di Priabona) crop out along

ridge tops and, in the case of Calcari Nummulitici, originate a marked karst morphology with

scattered groups of dolines. Eocene limestone are also found in the grabens of the area of Bosco

Chiesanuova.Finally, the most recent terms of stratigraphic succession are found in the vicinity of Verona,

represented by calcarenites and sandstone from the mid Miocene.

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Figure 23: Columnar basalts in San Giovanni Ilarione

4.2Structural layout

From a tectonic point of view, the Lessini Mountains have gone through extensional phases during

the ancient Mesozoic and Tertiary, a compressive phase in the Neogene and a southward tilting

phase in the Pliocene-Quaternary.

The faults originated in the Mesozoic have variable directions between North and NNE. They are

synsedimentary faults that formed at the margin of the Trentino platform, while this migrated

eastward in the Jurassic.

The faults originated during the initial phases of the Tertiary have a NNW direction, but can also

be found in the NNE directions, where they represent pre-existing faults later reactivated as left-lateral strike-slip faults (ZAMPIERI, 1995 and 2000). It is in this phase that the most significant

feature of the Lessini Mountains was established: the Alpone-Agno graben (localised in the eastern

portion of the area considered in this report), a structure linked to the Paleogenic extension (fig.

24) and accompanied by volcanism. At the same time, a complicated system of normal NNE and

NNW faults was activated in the central-western Lessini Mountains.

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Figure 24: Tectonic sketch of the Lessini Mountains (ZAMPIERI, 2000)

In the course of the Neogene, the ongoing compressive phase in the Southern Alps only slightly

involved the Lessini Mountains by producing the Corno dAquilio and Marana thrusts (CORSI &

GATTO,1964;ZAMPIERI,1991). The latter inverted the northern portion of the Alpone-Agno graben

(ZAMPIERI, 1995). During this phase, the pre-existing faults were reactivated as strike-slip faults.

During the Pliocene, the southward tilt phase begun (ZANFERRARI et al.,1982), which later evolved

in the SW direction due to the thrust caused by the NE migration of the Apennine foredeep

(DOGLIONI, 1993).

Evidence of neotectonics in the Lessini Mountains have been recognised by SAURO(1978), ZAMPIERI

(2000), and SAURO & ZAMPIERI (2001). The latter, in particular, have recognised some slopes

originated by extensional tectonics that have reactivated fault planes dating back to the early

Tertiary period in the Orsara area (upper Pantena Valley) and Scandole (Vajo dellAnguilla).

4.2.1 Tectonic structures in the central-western Lessini Mountains

This sector of the Lessini Mountains has been studied in detail by ZAMPIERI (2000) and as

summarized below, it is characterised by a rather complex structural configuration created by theexistence of two main systems of faults. The NNE-directed system is located in the central part,

while a NNW-oriented systems is found in the northern and central-eastern areas.

The area of interference between the two systems, which is localised among Bosco Chiesanuova,

Velo Veronese and Cerro Veronese, corresponds to a lowered rhomboidal structure within which

igneous rock intrusions and dolomitisation of the pre-existing rocky bodies took place.

The western margin of this structure is bordered by the fault of Bosco Chiesanuova, whose length

globally reaches ten kilometres, but which consists of three segments whose interconnection is

maintained by relay ramps.

This structure includes two minor grabens (Scardon and Mount Purghestal) with basalt and Eocene

calcareous rocks on their bottom. In particular, the basin of Mount Purghestal shows Eocene

calcareous blocks layers converging toward the centre of the graben, which leads to assume thatthe structure has appeared after the collapse in the roof of the magma caldera situated along a

lateral ramp of a fault in the NNE-oriented system (volcanic-tectonic basin).

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Another volcanic-tectonic basin is that of Mount Purga, near Velo Veronese. If we look at the map,

Mount Purga seems to be surrounded by normal faults and by basalt dykes from the Paleogene all

around. Consequently, this is another case where the opening of fractures along the connection

ramps between the various fault segments has led to the development of a rhomboidal basin where

a magma chamber has settled at low depth. Subsequently, the collapse of the roof of this chamber

seems to have formed the subcircular collapse basin of Mount Purga.

5 HYDROGRAPHIC FEATURES AND HYDROGEOLOGY

The major valleys furrowing the area of the Lessini Mountains are generally oriented N-S and

widen considerably while they converge toward the River Adige. The shape of these valleys, which

are rather deep, is the result of the combination of fluvial, karst, glacial and tectonic processes still

active today (SAURO, 1978; ZAMPIERI, 2000; SAUROand ZAMPIERI, 2001).

The drainage network is well developed, but inactive; this reflects the importance of the karst

phenomenon in this area. As a consequence, torrents have transitory flow rates determined only by

significant rainfall events.

Frequent specimens of valleys suspended above the main valleys are seen, whose origin can be

attributed to the rapid incision of valley floors in connection with recent tectonic upliftingmovements in the Lessini Mountains area, but also with the progressive karstification of the

network of dry valleys (SAURO, in SORBINI1993).

Four drainage basins can be identified:

Alpone Tramigna;

Vajo di Squaranto;

Progno di Valpantena;

Progno di Fumane.

As far as hydrogrology is concerned, the permeability of rock masses should be attributed to both

karst and the thick fracturation of lithotypes, where the latter phenomenon considerably increases

the secondary permeability of formations notoriously considered as scarcely permeable, such as,for example, Biancone and Scaglia Rossa. For this reason, formations in this area have been

assigned an average permeability due to fracturation, because the fractures pervading these rocks

have such a continuity as to establish communication between the relevant aquifers and the main

underlying aquifer. However, this absorption is so slow that the water has the time to establish a

superficial circulation. Only locally suspended aquifers feeding low discharge springs have been

detected.

Rosso Ammonitico is accounted for a different hydrogeological behaviour, with water penetrating

inside it following a high number of vertical flow directions (SAURO, 1973).

The underground runoff of water is very fast in the areas where Oolite di S. Vigilio and Calcari

Grigi formations crop out, as very large caves are found here, which contribute to determine a

substantially horizontal flow (PASA, 1954).The lithotypes found in the Lessini Mountains have been grouped under three main hydrogeological

categories:

an eastern group characterised by volcanic lithotypes, with low discharge springs;

a central-northern group with a predominance of jurassiccretacic limestones, with karst-

type springs;

a southern group characterised by cretacic and eocenic limestones and volcanic rocks: this

sector corresponds to the northern limit of the alluvial plain of the River Adige; springs are

of karst-type here and have limited flow rates.

The springs of the Lessini Mountains have variable discharges, closely depending on the local

hydrogeological conditions. Permanence times may range from a few months for the areas with a

primary porosity, up to a few days or a few hours for karst aquifers.

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There is a rather high number of springs at an altitude, which are characterised by temporary flows

and generally reduced discharges. These springs are closely dependent on meteoric events and are

essentially connected with localised epikarst systems having limited-size drainage basins.

The most important springs are located in the Fraselle Valley (which have been captured with

collection works below the river-bed), the Ossenigo springs (located in a small side valley on the

rocks hanging above the Adige Valley, and the Montorio springs.

5.1The Montorio springs

The Montorio springs (figs. 25 and 26) are a very interesting natural phenomenon from a scientific

point of view, due to both their hydro-structural arrangement and to their remarkable total

discharge (5 m3/s). The gravelly-sandy alluvia of the Montorio area have four adjacent springs

connected to a buried karst structure (30-40 m deep). These springs have been studied for a long

time, since 1889; in particular, there is an extensive study published in 1993 by the Town Museum

of Natural History of Verona. These springs consist in four small lakes located in Montorio, 60 m

a.s.l., which are directly supplied by karst channels placed in the Calcari Grigi formation.

Figure 25: Small sand volcanoes at the water emergence of Spring Fontanon in Montorio

The springs are located at the outlet of the Vajo di Squaranto, which looks like a deep river karst

canyon elongated in the N-S direction for an overall length of approximately 30 km and about 3-4

km wide. In particular, the flow rates of the four springs have been studied from June 1988 toMarch 1993 (ANTONELLIin SORBINI, 1993), during which period annual average rainfalls onto the

catchment basin considered were of 1080 mm, a value close to the 30-year average.

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The mean discharge of the springs, concerning the surface flow volumes, is about 5 m3/s. So, we

may assume that a non-negligible amount of this discharge is lost in valley floor alluvia. The

minimum discharge measured after a long and special period of drought was 1 m3/s, while the

maximum discharge was 11 m3/s (ANTONELLIin SORBINI, 1993).

Figura 26: The Spring Fontanon in Montorio

The discharge of these springs is characterised by a high synchronism and is closely connected with

the rainfall regime of the mountain area. Flood peaks are registered within 24-48 hours after the

main rainfall events and are related with channel karst and well developed circuits. The storage

volume estimated with the depletion curve method has been found to be 6107 m

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.Geophysical tests and the drilling of well for potable-irrigation water supply have shown that the

depth of the groundwater table in alluvia varies from 20 to 30 m in the northern sector of the valley,

from 15 to 10 m in the central area, and is reduced to 15 m in the southern section. The thickness

of alluvial materials filling the valley is rapidly increased southward, reaching over 100 m at the

outlet into the plain (ZAMBRANO, in SORBINI, 1993). The rocky substrate near Montorio is at least

30-40 m below the ponds.

The catchment basin upstream the Montorio springs extends for approximately 100 km2 and the

highest altitude reached is 1865 m (Cima Trappola). The hydrogeological basin of the springs has

been estimated to be of about 200 km2.

The Montorio springs have not been captured and the water, which was used by mills in the past

(fig. 27), now flow out feeding the Torrent Fibbio.

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Figure 27: Mill in the center of Montorio

In the 1988-1990 period, some samples of spring water and valley floor wells have been tested

(SORBINI, 1993). The quality of water was proved to be good: none of the per parameters examined

reached or exceeded the maximum admissible concentration for drinking use and nitrate levels

were among the lowest observed in the Verona area. The chemical-physical tests carried out

showed the prevalence of calcium bicarbonate, among salts, which proves that the water flows

inside calcareous rocks. The mean temperature is around 11 C, PH is 7.6.

Microbiological tests showed a temporary faecal contamination, with an increase in these levels

close to the first flood events immediately following periods of drought.

The quality of water in the karst reservoir was only partially altered by the high number of

potentially polluting activities existing in the Lessini area, particularly those related to thesettlements: about 10,000 inhabitants in the mountain area (there is a remarkable increase in the

number of inhabitants for tourist purposes in the summer and during Christmas holidays), farming

activities (about 30,000 heads of cattle, 60,000 swine and a few million chicken), and animal

breeding waste spilling. Furthermore, some cattle is taken up to the mountains for pasture in the

more than hundred malghe of the Upper Lessini during the summer.

6 HYDROGEOLOGICAL MAP

6.1Choices and criteria

In order to create a hydrogeological map, first of all we have collected geologic and hydrogeologic

data regarding the area to be represented. Then, based on these data, we have identified the

hydrogeologic units, consisting in geometrically contiguous groups of rocks (lithotypes) havingsimilar permeability features (fig. 28). The work was carried out following the guide-lines issued by

the National Geological Service (today APAT). The lithotypes cropping out have been grouped in

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units having homogeneous hydrogeological features and distinguished on the basis of their degree

of permeability.

Figure 28: Schematic hydrogeological sections of the Lessini Mountains. Keys pale blu: calcareous-dolomitic Unit,

pale green: marly-calcareous unit, dark green: marly-clayey Unit, olive green: calcareous Unit, brown: volcanic Unit,orange: colluvial and eluvial Deposit, red: main tectonic structures.

In figure 28 is shown the stratigraphic relation among the hydrogeological units; note the

difference between western and eastern Lessini, due to litho-stratigraphic variation in the two

areas.

The data contained in the basic geological map have been compared and integrated with other

thematic maps available at different scales and reprocessed to eventually obtain the

Hydrogeological Map here attached.

The Geological Map of the Natural Park of Lessinia (scale 1:40,000) has been selected among

the basic geological maps available and adopted, to be then integrated with the Sheets of the

Geological Map of Italy no. 35 Riva del Garda, no. 36 Schio, no. 48 Peschiera del Garda,

no. 49 Verona (scale 1:100,000). The Hydrogeological Map has then been drawn adding the

typical elements of the hydrogeology of the area (springs, wells, karst cavities, hydrography,

tectonics).

The map representation scale (1:50,000) was determined by the need to provide a good general

view of the different subjects represented with respect to the extent of the area (980 km2).

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Figure 29: Stratigraphic relationship among hydrogeological units outcropping in Lessini Mountains

6.2Hydrogeological units

Six hydrogeological rock units have been defined, with permeability related to fracturation and

karstification. The loos materials are divided into four classes, depending on their permeability

(related to porosity):

Calcareous-dolomitic unit: it includes dolomites and dolomitic limestones, which generally consist

of massif beds or have an undistinguished stratification. Permeability here is related to fracturationand karstification, and is locally remarkable. The complex has a thickness of several hundreds of

metres: altitude infiltrating water is propagated underground through the system of karst channels

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and gets to the springs situated at the base in extremely rapid times. Karst springs have discharges

that can reach even a few cubic metres per second, as in the Montorio case.

Marly-calcareous unit: it includes limestones ranging from mildly clayish to marly with

intercalations of marl and shale. Usually, it is thickly stratified and densely fractured, which

generally gives a medium level of permeability. Suspended water flows are found locally, whose

extension and thickness is limited (at different altitudes) and which supply a high number of smallsprings.

Marly-clayey unit: it includes thickly stratified marly limestones with important clayish and

organic-clayish intercalations. Permeability (related to fracturation) is low.

Calcareous unit: it includes marly limestones, compact limestones and nummulitic limestones with

macroforaminifers and lignitic intercalations. Permeability, related to karstification and porosity

(nummulitic limestones), is generally high.

Volcanic unit: it includes volcanoclastic rocks, sometimes stratified, breccias, hyaloclastites and

massive or altered basalt lava rocks. Permeability is generally low, locally variable depending on

the degree of clayey alteration.

Marly unit: it includes marls to more or less laminated marls. Permeability is low and locally

related to the degree of fracturation and fissuration.Eluvial and colluvial deposits: these are eterometric deposits with abundant clay matrix and

coarse skeleton: alteration and degradation blankets of volcanic and sedimentary rocks, fillings of

the main karst depressions and colluvial deposits at the foot of hill slopes and in the areas between

valleys. Permeability is generally very low.

Debris and alluvial deposits: these are valley floor alluvial deposits, alluvial fans, colluvia and

landslide deposits, consisting of elements with a largely variable grain size (from big blocks to

gravelly, sandy and/or muddy materials), characterised by a generally high permeability. Locally,

permeability may be reduced in the presence of cemented levels or very fine grain material.

Colluvial and glacial deposits: these generally consist of prevalently fine-grain materials derived

from the alteration of the bedrock and from heterometric accumulations with abundant silty matrix

of glacial origin. Permeability is generally very medium or low.

Muddy-clayey alluvial deposits: they include high-heterometry deposits ranging from big blocks to

fine or very fine-grain materials with a muddy-silty matrix, generally loose, sometimes cemented.

Permeability is generally low or very low.

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CONTENT

1. GEOGRAPHICALLOCATION.............................................................. .............................................................. 1

2. CLIMATICFEATURES................................................................ ............................................................... ......... 3

3. GEOMORPHOLOGY........................................................ ................................................................ ................... 5

3.1 Morphology.............................................................. ................................................................ ................... 5

3.2 Karstification ........................................................... ............................................................... .................... 83.2.1 Valle delle Sfingi or the Sphinx Valley..................................................... ................................................. 13

3.2.2 Covolo di Camposilvano.......................................... ................................................................ ................. 16

4 GEOLOGY............................................................. ................................................................ ............................ 16

4.1 Stratigraphical succession............................................................ ............................................................ 16

4.2 Structural layout ....................................................... ................................................................ ................ 19

4.2.1 Tectonic structures in the central-western Lessini Mountains ................................................................ ....... 20

5 HYDROGRAPHICFEATURESANDHYDROGEOLOGY................................................................ ................. 21

5.1 The Montorio springs......................................................... ................................................................ ....... 22

6 HYDROGEOLOGICALMAP...................................................... ................................................................ ....... 24

6.1 Choices and criteria........................................................... ................................................................ ....... 24

6.2 Hydrogeological units.............................................................................. ................................................. 26

Hydrogeological Map Monti Lessini

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Transcript of Hydrogeological Map Monti Lessini