The Remediation of the Adverse Effects of the Gravel Extraction in the Mostarsko Blato Catchment Area

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1 1 Paper N 0 : VI.07 The Remediation of the Adverse Effects of the Gravel Extraction in the Mostarsko Blato Catchment Area Mladen Zelenika, Božo Soldo, Damir Štuhec Abstract: Extraction of alluvial deposits at the weastern part of Mostarsko Blato, the gravel and sand from the Listica and the Mokasnica riverbed and surrounding area have adverse environmental impacts on quality and quantity of groundwater in use of the rural population. There are already very bad consequences for the private wells and the understandable complains to the authorities by fisherman, hunters, villagers and evironmentalists. The sink river water level and groundwater level in soil, dry water supply wells and reduce the productivities of gardens, and the compains are related to devastation of aquatic species, endemic plants and animals there, unpleasant noise from excavators, lorries etc. The field reconnaissance and complex analyzes of present environmental conditions at the devastated and surrounding unharmed areas is recommended including the documents related to pre-existing environmental conditions and establishe the systematic measurement of surface water level, groundwater level, level of sediments in the Mokasnica and the Listica, and changes in quality of water and biological productivity of soil at Project area. The mining operations should be reduced and stopped there and introduce the relevant remediation actions. Keywords: M. Blato, gravel, hydrological - hydrogeological data, object, environmental. 1. Introduction Dinaric karst in Republic of Croatia and Bosnia and Herzegovina are characterized by a great variety of natural environments and hence by an equally great variety of environmental problems. Catchment area Mostarsko Blato extends over more than 530 square kilometers, and approximately people reside in this area. The most important element of life in

2 524 Zelenika, Soldo, Štuhec catchment area Mostarsko Blato is unquestionably water, due to its abounded quantity during winter and scarcity during summer. Besides many periodical streams, the perennial streams: Listica, Crnasnica, Orovnik and Zvatic are flowing in this karstic catchment area to a naturally closed valley (polje) Mostarsko Blato. All area is scarce of water during the summer, but in the rainy season (winter), there is a flooded (lake) area of more than 25 square kilometers. Natural sink-holes (ponor) and for the last 50 years an artificial tunnel, evacuate all water to 200 m lower Jasenica river in the vicinity of only 5 km (see attached map). Exhaustion of gravel and sand from the Listica and the Mokasnica riverbed sources have adverse environmental impacts on quality and quantity of groundwater in use for rural water supply. This is one of very bad consequences of three years of war and conflicts in the region. Mayor routeways, activities, towns and villages are sided close to the Listica and the Mokasnica streams, where from come understandable complains to the authorities about devastation of aquatic species, including endemic plants and animals. More and more people demand the stark complex natural beauty and the peace and tranquility afforded by rivers. It is unfortunately replaced by lowered water level in the rivers and soil, dry water supply wells and land, unpleasant noise from excavators, lorries etc. Only few local contractors have short-time license to mine gravel and sand there, but the mining continues almost 10 years, even it should be stopped, and demand of the aggregate should be met using the crushed rock (limestones) at an adequate site. The present devastation should be urgently surveyed and analyzed, designed the most effective remedial measures ad recommendation. Implementation may take place at the only those sites where the methods of work and process are acceptable for all users of water, land, forest etc. 2. Hydrometeorological and climatological data The climate in the area of Mostarsko Blato has mixed mediterranean and continental characteristics. It is generally humid, with moderately dry summers. The average yearly precipitation is mm/year. The minimum, during the analyzed period between 1989 and 1961, was 910 mm (1938), and the maximum 2748 mm (1900) (Zavod za hidrotehniku, 1963). The average number of days with precipitation in a single year is 140. The precipitation in December is four times bigger than in July and the total average precipitation for the period between November and January (693 mm) is three times bigger than in the period from June to August (227 mm) (Energoinvest, 1981). When these data are combined with the effects of increased evaporation and evapotranspiration in the summer months it is clear why problem of seasonal water shortage exists in this area. The average air temperature in the area of Mostarsko Blato is 14 C 0, the minimum is 15 C 0 and maximum 42 C 0. Within each year there are approximately 40 to 50 hot days with temperatures above 30 0 C and only 1 or 2 days in winter with maximal daily temperatures bellow 0 0 C. As per meteorological observatory Mostar, the yearly aerodynamic conditions in the Mostarsko Blato are as follows: There are only 60 quite days/year, approximately 300

3 The Remediation of the adverse Effects of the Gravel Extraction in the Mostarsko Blato Catchment Area 525 windy days/year (bove 4 m/s), 160 days/year (above 12 m/s),) and 20 days/year (above 20 m/s), strong wind blows more than half time and it is mostly bura, the cold northern wind typical for this region. 3. Hydrological data The estimated orographic drainage area of the Mostarsko Blato is around 530 km 2. However due to the possible underground connections, orographic boundaries may not coincide with the actual limits of the Mostarsko Blato catchment area. The inflow of four rivers Listica, Mokasnica, Crnasnica, and Zvatic in to the Mostarsko Blato, (including the water from irrigation channels), has been estimated as 534 x 106 m 3 or approximately 16,6 m 3 /s. However, this value must be increased for the substantial amount of water brought in by numerous streams that flow directly into the Mostarsko Blato, and drain approximately 180 km 2 of the drainage basin (Orovnik, Blaz, Gromolj, Kacun, Zelenikove Babe, Đolina Draga, Zvec, Dragana, Zukanovina, Arine and other). Figure 1 Sketch of exploring works and hydrogeological appearances The water that leaves the polje through swallow holes (ponor) and the evacuation tunnel with a capacity of 40 m 3 /s is diverted to the river Jasenica. The value of 16,6 m 3 /s for the average flow of Mostarsko Blato, that was determined on the basis of existing hydrological data is substantially higher than the flow of the river Jasenica, 10,92 m 3 /s, and the difference between these two values is retained in the polje in a form of floods. Flood waters occur yearly in the Mostarsko Blato area, in registered amount of HQ/20=258 m 3 /s.

4 526 Zelenika, Soldo, Štuhec Four main monitored watercourses: Listica, Crnasnica, Mokasnica and Zvatic provide bulk of the water in the polje, and their total Q max equals 339,16 m 3 /s, (Energoinvest, 1981). Ther monthly average flow rates are shown in Table 2. The table also contains information about periods of observation for a characteristic entrance profile and position and elevation of the respective gauging station. Valuable hydrological data for the area can be obtained from six gauging stations on the streams Ugrovaca (1), Listica (2), Crnasnica (1), Mokasnica (1) and Zvatic (1) and four gauging stations on the points of outflow from the polje: Krusevo swallow hole, and Jasenica (3) (Energoinvest, 1981). However, the data from the existing measurement stick in the Mokasnica and Mokro polje are not available and information similar to those presented in table 1 are nonexistent for the numerous smaller streams, which strongly influence Mostarsko Blato. Table 1 Mean monthly and yearly inflows in Mostarsko Blato Flow rate (m 3 /s) LISTICA CRNASNICA MOKASNICA ZVATIC PAHE M.B. Profile Uzar. Bridge Knespolje Jare Zvatic Σ Elevation of 240,56 236,35 232,52 232,74 ( >222,20) 0 profile Period of observation January 27,82 0,928 1,790 1,170 18,40 February 26,79 0,947 1,800 1,240 16,40 March 17,40 0,840 1,290 0,966 21,10 April 16,40 0,850 0,936 1,030 25,60 May 13,46 0,748 0,731 0,695 23,30 June 4,86 0,540 0,173 0,371 11,00 July 1,35 0,348 0,038 0,190 4,00 August 1,46 0,274 0,042 0,139 1,30 September 4,00 0,391 0,152 0,337 2,70 October 8,44 0,579 0,457 0,419 12,00 November 21,60 0,815 0,828 0,965 27,00 December 28,08 0,950 1,410 1,080 26,50 Q year 14,30 0,684 0,766 0,716 15,76 Q max 319,46 3,050 12,580 4, ,16 Q min Dry 0,03 dry 0,00 0,03 * *Approximately 1m 3 /s of water is taken through irrigation channels away from river Listica and they are not included in the values from the table Values of the basic hydrological parameters have not yet been determined for the Mostarsko Blato area. Presented values are from literature and pertain to Adriatic part of Croatia and Bosnia and Herzegovina (Sekulic and Vertacnik): Average precipitation: 1,385 mm/year - Evapotranspiration 545 mm/year - Average inflow by surface streams: 554 mm/year - Direct flow in to the see 23 mm/year - Subsurface drainage 225 mm/year - Submarine springs 41 mm/year.

5 The Remediation of the adverse Effects of the Gravel Extraction in the Mostarsko Blato Catchment Area Hydrogeological data There are two collectors of underground water in the Mostarsko Blato area: Cretaceous limestones (Mesozoic) and Quaternary deposits of gravel, sand and limestone debris. Smaller amounts of underground water can be captated also in the Tertiary limestones and marls (Cenozoic) and these deposits have a significant meaning for rural water supply (i.e. Dobrinjska Draga at Crnac or excavated wells near Privalj). In the periods of heavy precipitation, intermittent springs and rain water flow in the streams of: Ugrovača; Mostina, Dragana, Zukovina, Zvec, Zelenikove Babe, Kacun, Gromolj, Blaz, Mokasnica etc. Thes intermittent springs are related to the cretaceous (upper) aquifer. The perannual springs of Listica, Crnasnica, Zvatić and Orovnik are also related to the cretaceous aquifer It has been noted that despite aerial distance of only 10 km between bore holes PB-5 in Dobric and PB-10 in Ljuti Dolac, difference in the water levels between the two bore holes reaches in dry season up to 87 meters (Sliskovic & Zelenika, 1998). This phenomenon indicates that, western part of the polje is completely isolated from the eastern part by the deposits with smaller permeability. These sediments include 70 m thick Qaternary impermeable clay deposits, some possible marl deposits of Neogene age and probably clayey limestones of Cretaceous or sometimes Tertiary age. Existence of such layers is the main cause for the formation of the springs of Crnasica, Zvatic and Orovnik and for the permanent flow of Mokasnica in the lower part. The deposits of the Quaternary age have thickness between 10 and 70 m. and even 150 m. They are discordantly deposited over the paleorelief formed on the Mesozoic carbonates. Quaternary deposits consist mainly of gravels and sands, brought by the rivers in the western part of the polje and by the longer nonpermanent flows along the edges of the polje. Clays and other lake sediments occur in the eastern and central parts of the Mostarsko Blato, and carbonate debris mixed with clay is present along its edges at the various depths. Vast areas covered with fine sand occur on the southern side of the polje in the area of Podgorje, Ljuti Dolac, Jare, and Biograci, (Zukanovina, Kraljevine, Odanci, Dubovi, Lokve, Njivice etc). The sand was brought in to the polje by rivers and streams and deposited during flood periods through the wave activity induced by the bura wind. In the dry periods force of wind a main agent controlling sand distribution. Wells with depths from 1.5 to 5 m have been excavated along the edges of the polje and used for the water supply of local rural population. Tens of such private wells existed in Knespolje, Uzarici, Jare, Biograci, Ljuti Dolac, Polog, Dobric and Gradac. Earlier, the wells have been dug manually but now they are mostly excavated with mechanical equipment, usually on the approximate elevation between 225 and 235 m. Groundwater is captated in the alluvial aquifer, consists of gravels and sandy gravels, rarely in debris, at the depths of 2 or more meters. It is used for the irrigation of the agricultural surfaces (vegetable) and for the supply of the households in the periods when cisterns (reservoirs for collected rain water) go dry. This thin aquifer extends

6 528 Zelenika, Soldo, Štuhec from the central to the southern, western and northern edges of the polje. However, it thins gradually, and disappears around Kaluza in the eastern direction. Gravels and sands used to be a natural source of water for the springs of the important peranual tributaries to lištica and Mokašnica rivers were flowing through the central areas of the polje. Zones of swallow holes is in the eastern part of the Polje, near Polog and in the larger part of the area near Krusevo, carry the water from the Mostarsko Blato towards to lover parts of the river Jasenica/Neretva. 5. Hydrotechnical objects in the MostarsKO BLAto During the dry summer season hydrotechnical measures (irrigation) are necessary in the area of Mostarsko Blato to ensure water for agricultural production. One of the first such projects in the area, was construction of the channel that takes water from the lower part of the river Mokasnica, near permanent spring Bilila, towards southeast, and irrigates some plots in Biograci. An earthen dam, approximately one meter high, was built for this purpose in Mokosnica river upstream from the spring. At the time of its construction, the spring has provided minimal amounts of water to the lower part of the river and the overall effects were relatively favourable. During 1950 earthen dam was repleaced with a concrete one which collapsed 15 years later due the weak footing. However, remaining water was later diverted from Mokosnica and its tributary at locality Kaluža to irrigate downstream fields in Ljuti Dolac. The consequence of this measure was drying out of the lower flat part of the river with the devastating effects on the aquatic life and fish population. The tunnel with a length of approximately 1527,7 m and a connecting channel with a trapezoid cross-section (196 m long) take flood waters from Mostarsko Blato at the elevation 222 m near Krusevo to river Jasenica at elevation 48,30 m. The new 9488-m long drain passes trough the center of the Mostarsko Blato and it has numerous harmful effects for the environment in the polje. The lower parts of river Moksnica become dry, and generally, the level of groundwater has been lowered for 1,5 m to 2,5 m causing destruction of numerous unique marsh habitats at Mostarsko Blato. 6. Problem analyzes Since the rivers Listica and Mokasnica have many bars and low water beds, the extraction of gravel and sand for construction of civil structure is convenient and low cost. It is estimated that more than 5 million cubic meters of gravel and sand have been extracted in 6 km long stream of Listica from Uzarica to Polog and approximately 3 km long stream of Mokasnica in Biograci. After the hydrologic reconnaissance of the mentioned devastated parts of rivers, the following impacts could bee stated.

7 The Remediation of the adverse Effects of the Gravel Extraction in the Mostarsko Blato Catchment Area Environmental impacts Suspension of sediments The mechanical disturbance created by the dredging process stirs up clouds of fine silt, and wastewater entering the river from gravel washing plant contains heavy concentration of fine particles. Sediments from these sources reduce light penetration, and settle, blanketing the riverbed. These impacts impair the respiration and photosynthesis of submerged aquatic plants, and reduce growth rates or cause death. The reduction in the extent of these vital habitats deprives river fauna of refuge from predators, and eliminates feeding and breeding areas. Fine settled particles make unsuitable spawning grounds for fish in Listica and Mokasnica, and thus sedimentation affect fish breeding Reduction in the natural capacity to take up sewage nutrients Vegetated, shallow water areas in fat-flowing rivers have substantial capacity to assimilate nutrients in domestic and wastewater from other sources. Gravel and sand-mining leads to the removal of large areas of shallows, and the lower water velocities in the dredge hole dramatically reduced the efficiency of nutrient removal. Increased nutrient availability stimulates algal blooms and the growth of surface weed mats. Dense plant growth reduces the appeal of the water body and shades out life beneath (Mokasnica). Algal blooms may taint and color the water and release toxic substances, which are potentially hazardous to livestock and public health. These changes in water quality are detrimental to fish. The decline in aesthetic quality of the riverscape depresses owners of surrounding land, fishing activists, tourists and many others. Organic matter may decompose in the sluggish waters of the borrow pit. It should be investigated because the accompanying decline in water quality may have an adverse effect of fish and the aquatic life and on the potable groundwater in water supply wells in Biograci, Jare, Polog, Dobric, Knespolje and Uzarici. These reasons justify a ban on extraction of gravel in zones where other activities must not be put in jeopardy. The critical zones should be determined by adequate program of investigation Erosion of the river bed and banks The extraction of material from riverbed deepened the channels and enlarged the cross sectional areas of the rivers Listica (1 to 3,5 m) and Mokasnica (0,5 to 2 m). These resulted in more extracted quantity of material than the natural supply of sediments, lowering of the water level, and adverse erosion upstream and downstream for a distance from 1 to 5 km from the pits. Intensification of erosion on some places has destabilized the river banks. It may lead to collapse of some wells, pump-stations and even a bridge Clogging of the bed of the borrow pits The slower rate of water flow in the borrow pits causes the deposition of fine sediments and organic matter held in suspension by the rivers Mokasnica and Listica. The sediments clog the bed of the borrow pit, so prevent filtration of river water into the aquifer. The cumulative impact of the 15 years of aggregate extractions has reduced groundwater replenishment and

8 530 Zelenika, Soldo, Štuhec level for more than 2 m. Therefore groundwater became critical in the western part of Mostarsko Blato, where crop failure occurred, grazing pastures were lost, many water supply wells run dry as well as springs of smaller water flows Aesthetic quality Extraction machinery and piles of sand reduced the aesthetic quality of the riverscape. Consideration should be given to the research of feasibility of planting desirable natural barriers to screen the extraction area Noise Local people already reported that the increased mechanical noise at the extraction site discouraged migratory birds. Majority of water birds already moved to other more suitable areas. Research needs to determine the importance of Mostarsko Blato, Listica and Mokasnica rivers as a migratory birds stop-over. Road haulage of gravel and sand involved higher noise and vibration levels. Transport of gravel, encouraged the passing of more private vehicles through these illegal roads and increased the risk of road accidents and of pouring out the fuels and lubricant in that fragile terrain. 7. Recommendation of the project monitoring and remediation needs In order to remedy the consequences the mining at Mostarsko Blato, a field reconnaissance should be done, and complex analyzes of present environmental conditions at the devastated and surrounding unharmed areas. The documents related to pre-existing environmental conditions, should be studied. Approximately 10 bench-marks should be be installed on the best suitable sites in the project area. In the first phase of this project the baseline data should be established through the systematic measuring at bench-marks and other places in the area of gravel extraction and its influence. The measurement of surface water level, groundwater level, level of sediments in the Mokasnica and the Listica, and changes in quality of water and biological productivity of soil at Project area will cover all seasons of the year. The baseline data enable comparisons of the existing conditions in the area of mining operations influence and pre-existing environmental conditions, Pre-existing data could be imagined from earlier documents and through observations at unharmed areas out of effect of mining operations. A monitoring program will be initiated to continue throughout time after the project. The data collected should be analyzed and findings fed back into restoration works. The monitoring may include the following: changes in water quality, including nutrient status, salinity, turbidity and sedimentation patterns; changes in the hydrological regime, including fluctuations of flood, river flows and the level of the water table;

9 The Remediation of the adverse Effects of the Gravel Extraction in the Mostarsko Blato Catchment Area 531 changes in faunal diversity and abundance; alternation of landforms, e.g. river bed, stability of banks; interference with significant archeological site - Sarampovo. The potential environmental hazards may be avaluated and then the adequate measures could be proposed to avoid further hazards. The collected data may be the support to take proper action to remedy the area. References Đurović, M (1964), Hidrološka studija i melioracija Mostarskog Blata, Gradjevinar br.2, god VI. Zagreb. Energoinvest (1981): kratak prikaz podloga parametara i koncepcija tehničkih rješenja, Energoinvest, Higraižinjering, Sarajevo. Sekulić, B,. Vertačnik., A (1996)., Balance of average annual fresh water inflow into the Adriatic Sea, Water Resources Development, vol. 12., br 12. Slišković, I. (1996): izvješće o hidrogeološkim istraživanjima za vodoopskrbu Mjesne zajednice Ljuti Dolac, Hidrogeoing, Široki Brijeg. Slišković, I., and Zelenika M.., (1998): Hidrogeološka karta sliva Mostarskog blata u mjerilu 1:25000 i hdrogeološki profili, Varaždin. Thomann, R. V., Lobos, J. E., Salas, H. J. & Dos Santoa, J. L. (1987): Manual de evaluacion y manejo de sustancias toxicas en aguas supericiales, (3) Evaluacion preliminar del problema. CEPIS Technical Report. Zavod za hidritehniku (1963): Hidrološka studija Mostarskog Blata Dio I i Dio II, Zavod za hidrotehniku Građevinskog fakulteta sveučilišta u Zagrebu. Authors Mladen Zelenika: Faculty Civile Enginering Mostar, Bosnia and Herzegovina Božo Soldo: Geotechnical faculty, Varaždin, Croatia Damir Štuhec: Geotechnical faculty, Varaždin, Croatia