Hydrology Baseline Report (all watercourses except Rivers Liakhvi and Supsa)

Transcription

1 Section 3.2a Hydrology Baseline Report (all watercourses except Rivers Liakhvi and Supsa) NOTE: The survey was undertaken on a previous version of the route, therefore some of the crossings surveyed differ from those of the final alignment. The maps have been updated to show the current alignment.

2 Table of Contents 1 Introduction Survey Scope of Work Hydrology Survey Findings Overview River Aliskhevi River Lochini River West Tortla Literature Sources... 3 Appendix 1 Maps of Intersected Watercourses and Catchment Areas... 4 Appendix 2 Characteristics of Intersected Watercourses Appendix 3 Photo-documentation Tables Table 1 WREP Sections Covered by... 1 Photos Photo 1 River Aliskhevi Crossing Photo 2 River Aliskhevi, Downstream of Crossing Photo 3 River Aliskhevi, Upstream of Crossing Photo 4 River Lochini-1 Crossing Photo 5 Downstream of River Lochini-1 Crossing Photo 6 Upstream of River Lochini-1 Crossing Photo 7 River Lochini-4 Crossing Photo 8 Downstream of River Lochini-4 Crossing Photo 9 Upstream of River Lochini-4 Crossing Photo 10 Jokhtaniskhevi Crossing Photo 11 Downstream of Jokhtaniskhevi Crossing Photo 12 Upstream of Jokhtaniskhevi Crossing Photo 13 Gully 3 Crossing Photo 14 Downstream of Gully 3 Crossing Photo 15 Upstream of Gully 3 Crossing Photo 16 River Jachviskhevi Crossing Photo 17 Downstream of River Jachviskhevi Crossing Photo 18 Upstream of River Jachviskhevi Crossing Photo 19 Gully 4 Crossing Photo 20 Downstream of Gully 4 Crossing Photo 21 Upstream of Gully 4 Crossing Photo 22 Gully 8 Crossing Photo 23 Downstream of Gully 8 Crossing Photo 24 Upstream of Gully 8 Crossing Photo 25 River West Tortla Crossing Photo 26 Downstream of River West Tortla Crossing Photo 27 Upstream of River West Tortla Crossing April 2009, updated December 2012 and August 2016 Page i

3 1 INTRODUCTION Dzelkva Ltd - Georgian environmental consultancy was commissioned by Georgian Pipeline Company (GPC) to undertake a hydrology field survey of all watercourses traversed by the proposed replacement / re-route sections of the Western Route Export Pipeline (WREP). The fieldwork was conducted by B. Ukleba, hydrologist in mid April, The sections covered by the survey are summarised in Table 1. Table 1 WREP Sections Covered by Start AM End AM Target WREP Section Length, m RP-001 (out of scope except for section RP-001a) 18, RR-001 6, RR-001a (out of scope) 1, RP-002 (out of scope) 2, RP-009/6 (out of scope) 7, RP-007/8 (out of scope) 23, RR-004a RR-007 (out of scope) 100 The scope of the survey is detailed in Section 2 below. The watercourses crossing the target WREP sections are discussed in Section 3 and shown on Maps 1-9 contained in Appendix 1. Characteristics of all intersected watercourses as specified in Section 2 below are given in Appendix 2 while Appendix 3 contains photo-documentation. 2 SURVEY SCOPE OF WORK The survey identifies and characterises all watercourses crossed by the RR Sections originally proposed in 2009, other than the Supsa which is addressed in a separate report. As indicated in Table 1 above, most of the rivers are no longer within the scope of the WREP-SR Project; however information about these rivers provides valuable background hydrological information for WREP and has been included in this report. The following data was recorded for each crossing: GPS location of crossing Approx AM of crossing Photo upstream and downstream Width and depth of water flow Width and depth of channel Upstream catchment area Downstream sensitive receptor (e.g. r. Mtkvari, Tbilisi reservoir), and distance to downstream receptor Flow rate - approx. Type of watercourse - natural/canalized, natural/man-made, or an irrigation channel. April 2009, updated December 2012 and August 2016 Page 1

4 3 HYDROLOGY SURVEY FINDINGS 3.1 Overview The previously proposed re-route (RR) and replacement (RP) sections of the WREP cross several watercourses, including rivers, gullies and channels. Of particular note are rivers Aliskhevi, Lochini (crossed by the pipeline corridor four times) and West Tortla. Brief characterization of these rivers is given in Sections below. These rivers are not crossed by any of the re-routes of the current scope of WREP-SR Project, but are similar to smaller watercourses that will be crossed by the Project. 3.2 River Aliskhevi The river source is located on the southern slope of Ialno ridge at the altitude of 1,680m amsl. The Aliskhevi flows into river Lochini approximately 3.5 km east of village Lilo. The water catchment area at the pipeline crossing is 51.8 km 2 ; river length is 15.4km, total fall (difference in altitudes between the source and confluence) - 1,000 m, average gradient - 65%. Several tributaries of I category flow into the Aliskhevi upstream of the crossing; total legth of the upstream tributaries is 11.8 km. The river basin is clearly divided into mountainous and lowland zones. The geological structure of the mountainous part is composed of sandstones, marls and old conglomerates while that of the lowland part is represented by recent alluvial layers. Forest cinnamonic soils of loamy composition are mostly found in the river basin. Deciduous forest occurs in the upper part of the basin while the lowland zone is largely used for agriculture (various agricultural crops). The river gorge is of V-shape from the source to village Martkopi, downstream it first assumes a boxlike shape, then turning into a trapezium. The river bed is moderately meandering and insubstantially branched. Alluvial isles created due to branching are overflooded by water of 1.0 to 1.7 m depth during flash floods. The river is recharged by snow, rain and groundwater. The latter contribution to the recharge is insignificant. River water regime is characterised by spring floods due to snowmelt, summer-autumn flash floods caused by rain and instable low water level in winter. It should be noted that flash flood levels caused by autumn rain substantially exceed that of spring floods resulting from the snowmelt. Low water level in winter is frequently disrupted by flash floods resulting from rain. 3.3 River Lochini The river source is located on the eastern slopes of the southern-western branch of Ialno ridge. It is formed via confluence of Patara-Khevi and Tsirdlis-Khevi at the altitude of 785 m amsl east of mt. Saghindzle (1,337 m amsl). It flows into r. Mtkvari. The river Lochini basin is clearly subdivided into mountainous and lowland parts. The geological structure of the mountainous part is formed by sandstones, marls and old conglomerates while that of the lowland zone is represented by relatively recent alluvial layers. Forest cinnamonic soils of loamy composition are mainly found in the river basin. Deciduous forest occurs in the upper part of the basin while the lowland zone is largely used for agriculture (various agricultural crops). The river gorge is a trapezium along its entire length. The gorge slopes merge with adjoining ridge slopes. Close to the confluence, the river flows in the left terrace of r. Mtkvari and its gorge is not clearly delineated. The terraces are found along entire length of the Lochini. Terrace height is 2-3 m, width m, length m. In the upper part of the basin the terraces are covered by herbaceous vegetation and shrubbery while they are mostly used for agriculture in the lowland part. April 2009, updated December 2012 and August 2016 Page 2

5 The river bed is moderately meandering and mostly without branches. The water flow width varies from m (upper reaches) to m (lower reaches) while water flow rate ranges from 0.8 m/sec to 1.2 m/sec. River Lochini is recharged by snow, rain and groundwater. Contribution of the latter is secondary. The river water regime is characterized by spring floods due to snowmelt, summer-autumn flash floods resulting from rain and instable low water level in winter. It should be noted that flash flood levels caused by autumn rain substantially exceed that of spring floods resulting from the snowmelt. Low water level in winter is frequently disrupted by flash floods resulting from rain. River Lochini is used for irrigation. 3.4 River West Tortla River West Tortla (Bersheula / Kirbalula) source is located approximately 2.5 km south-west of village Kveda Tsolda, at the altitude of 1,400m. It flows into r. Mejuda in the vicinity of Gori. River length is 31 km, total fall - 813m, average gradient 26.2%, water catchment area 197 km 2, average altitude - 750m. The river has several minor tributaries. The geological structure of the basin is composed of the Tertiary sediments overlaid by clayey and loamy soils. Deciduous forest is developed in the upper reaches while the lower part is mostly used for agriculture (various agricultural crops). The river gorge is narrow in the upper reaches becoming wider downstream. It is not clearly delineated in Shida Kartli lowland where the river bed is highly meandering and branchless. Here the flow width varies from 2m to 6m, depth - from 0.1m to 0.6m and flow rate - from 0.4 m/sec to 1.0 m/sec. The river is recharged by snow, rain and groundwater. The water regime is characterized by spring floods, autumn flash floods and instable low water level in summer and winter. The river is used for irrigation via several minor irrigation channels laid by local residents. 4 LITERATURE SOURCES 1. Soil Map of Georgia. Editor - E. Gamkrelidze. Tbilisi, Soil Map of Georgia. Editor - T. Urushadze. Tbilisi, Ukleba D., Physico-Geographical Zoning of Eastern Georgia. In Georgian. Tbilisi, Sabashvili M., Soils of Georgian SSR. In Georgian. Tbilisi, Javakhishvili Sh., Climatography of Georgia. In Georgian. Tbilisi, Geology of USSR, Vol. X, Georgian SSR, Part I. In Russian. Moscow, Geomorphology of Georgia. In Russian. Tbilisi, 1971 April 2009, updated December 2012 and August 2016 Page 3

6 APPENDIX 1 MAPS OF INTERSECTED WATERCOURSES AND CATCHMENT AREAS April 2009, updated December 2012 and August 2016 Page 4

7 April 2009, updated December 2012 and August 2016 Page 5

8 April 2009, updated December 2012 and August 2016 Page 6

9 April 2009, updated December 2012 and August 2016 Page 7

10 April 2009, updated December 2012 and August 2016 Page 8

11 April 2009, updated December 2012 and August 2016 Page 9

12 April 2009, updated December 2012 and August 2016 Page 10

13 April 2009, updated December 2012 and August 2016 Page 11

14 April 2009, updated December 2012 and August 2016 Page 12

15 April 2009, updated December 2012 and August 2016 Page 13

16 APPENDIX 2 CHARACTERISTICS OF INTERSECTED WATERCOURSES April 2009, updated December 2012 and August 2016 Page 14

17 No. Gully No and River Name AM Location Crossing Coordinates X Y Upstream Catchment Area, km 2 Flow Width, m Flow Parameters Depth, m Rate, m/sec Channel Parameters Width, m Height 1, m Watercourse Type Natural Artificial Modified Distance to Downstream Receptor Note R. Aliskhevi km to r. Not in scope Lochini included for 2 R. Lochini km to r. Mtkvari 3 R. Lochini km to r. Mtkvari 4 Gully km to r. Mtkvari 5 Jokhtaniskhevi km to r. Mtkvari 6 Gully km to r. Mtkvari 7 Gully 3 S of km to r. Mtkvari information Not in scope included for information Not in scope included for information Dry Not surveyed in 2009 Dry; there is a road in the gully. There are 2 houses near the xng. The route is likely to cross their land plots. No 1 Maximum water level at peak flows (flash floods) April 2009, updated December 2012 and August 2016 Page 15

18 No. Gully No and River Name AM Location Crossing Coordinates X Y Upstream Catchment Area, km 2 Flow Width, m Flow Parameters Depth, m Rate, m/sec Channel Parameters Width, m Height 1, m Watercourse Type Natural Artificial Modified Distance to Downstream Receptor Note inhabitants were noticed during the fieldwork 8 R. Jachviskhevi S of km to r. Mtkvari There is a steel pipe in the riverbed at Jachviskhevi xng creating a waterfall effect; due to this the bed is washed out to a depth of 2-2.5m downstream of the pipeline 9 Gully km to r. Dry Mtkvari 10 Gully Not surveyed in Gully Not surveyed in Gully 7 SE of Not surveyed in 2009 April 2009, updated December 2012 and August 2016 Page 16

19 No. Gully No and River Name AM Location Crossing Coordinates X Y Upstream Catchment Area, km 2 Flow Width, m Flow Parameters Depth, m Rate, m/sec Channel Parameters Width, m Height 1, m Watercourse Type Natural Artificial Modified Distance to Downstream Receptor Note Gully 8 S of km to r. Aragvi A 1,500mm leaking water pipe passes through the left slope of the gully (likely for supply of Tbilisi). The spilt water flows into the gully. The 11 R. West Tortla SE of km to r. Mejuda gully itself is dry Not in scope included for information April 2009, updated December 2012 and August 2016 Page 17

20 APPENDIX 3 PHOTO-DOCUMENTATION April 2009, updated December 2012 and August 2016 Page 18

21 Photo 1 River Aliskhevi Crossing Photo 2 River Aliskhevi, Downstream of Crossing April 2009, updated December 2012 and August 2016 Page 19

22 Photo 3 River Aliskhevi, Upstream of Crossing Photo 4 River Lochini-1 Crossing April 2009, updated December 2012 and August 2016 Page 20

23 Photo 5 Downstream of River Lochini-1 Crossing Photo 6 Upstream of River Lochini-1 Crossing April 2009, updated December 2012 and August 2016 Page 21

24 Photo 7 River Lochini-4 Crossing Photo 8 Downstream of River Lochini-4 Crossing April 2009, updated December 2012 and August 2016 Page 22

25 Photo 9 Upstream of River Lochini-4 Crossing Photo 10 Jokhtaniskhevi Crossing April 2009, updated December 2012 and August 2016 Page 23

26 Photo 11 Downstream of Jokhtaniskhevi Crossing Photo 12 Upstream of Jokhtaniskhevi Crossing April 2009, updated December 2012 and August 2016 Page 24

27 Photo 13 Gully 3 Crossing Photo 14 Downstream of Gully 3 Crossing April 2009, updated December 2012 and August 2016 Page 25

28 Photo 15 Upstream of Gully 3 Crossing Photo 16 River Jachviskhevi Crossing April 2009, updated December 2012 and August 2016 Page 26

29 Photo 17 Downstream of River Jachviskhevi Crossing Photo 18 Upstream of River Jachviskhevi Crossing April 2009, updated December 2012 and August 2016 Page 27

30 Photo 19 Gully 4 Crossing Photo 20 Downstream of Gully 4 Crossing April 2009, updated December 2012 and August 2016 Page 28

31 Photo 21 Upstream of Gully 4 Crossing Photo 22 Gully 8 Crossing April 2009, updated December 2012 and August 2016 Page 29

32 Photo 23 Downstream of Gully 8 Crossing Photo 24 Upstream of Gully 8 Crossing April 2009, updated December 2012 and August 2016 Page 30

33 Photo 25 River West Tortla Crossing Photo 26 Downstream of River West Tortla Crossing April 2009, updated December 2012 and August 2016 Page 31

34 Photo 27 Upstream of River West Tortla Crossing April 2009, updated December 2012 and August 2016 Page 32

35 Section 3.2b River Liakhvi Report 2016 Note: This crossing was replaced in 2013/14, but the results are included in the ESBR as the river may be used as a source of hydrotest water

36 Table of Contents 1 Introduction Field Survey Scope and Methods Brief Hydrological Description of River Liakhvi... 1 Table of Figures Figure 1 Boulder barrier, existing WREP crossing, r. Liakhvi... 3 August 2011 Page i

37 1 INTRODUCTION This report summarises the findings and observations made in the course of the hydrological survey of the proposed River Liakhvi crossing point (AM 142). The survey was conducted on 2nd August, The team was composed of the following Dzelkva personnel: Baadur Ukleba, hydrologist, and Irakli Tandashvili, field assistant. 2 FIELD SURVEY SCOPE AND METHODS The hydrological field survey involved the surveyors walking 200m downstream and upstream of the proposed crossing and a 100m wide strip on both banks of the Liakhvi river around the proposed crossing. The survey areas were identical to those covered by the ecological baseline survey (i.e. botanical and zoological surveys). The survey was carried out as described in Section 3.1 of the E&S Baseline Report. 3 BRIEF HYDROLOGICAL DESCRIPTION OF RIVER LIAKHVI The source of the River Liakhvi is located in the vicinity of village Goluata at an altitude of 2,337 m. The Liakhvi is a left tributary of the Mtkvari river with the confluence located at the altitude of 972 m near Gori. The river length is 98 km with a total fall of 1,755 m, an average inclination of 17.9% and a total basin catchment are of 2,440 km 2. The average altitude is 1,590 m. The river is divided into three branches in the vicinity of the proposed crossing; the total width is 279 m. The average depth at the crossing point is 0.55 m and the flow velocity does not typically exceed 2 m/sec. The Liakhvi has 591 tributaries, their total length is 1,800 km. The largest tributaries are the Patara Liakhvi (length 63 km) and the Mejuda (length 46 km). The river basin is located on the southern slope of the Caucasus ridge. It is enclosed by Racha and Surami ridges to the west, Kharuli ridge to the east and the Mtkvari river lowland to the south. The river basin is divided into high mountainous, foothills and lowland sections. The high mountainous part of the basin was subject to severe glaciation in the past, which is confirmed by presence of corries, troughs and moraines. The basin includes 12 glaciers with a total area of 5.5 km 2 within the boundaries of the Caucasus ridge. The high mountainous part of the basin is comprised of slatey clays, marls and limestones. The foothill part is composed of sandstones and slatey clays while the lowland part is comprised of old and recent alluvial sediments. The basin vegetation is characterised by vertical zoning. Shrubbery is found in the lowland part, mixed forest occurs in the foothills up to 1,000-1,100m altitudes while sub-alpine and alpine meadows are found in the high mountainous part. Almost 32% of the basin is occupied by forest. The first section of the river (from the source to village Kekhvi) is 56 km in length; its valley is terraced; terrace surfaces are even, slightly dissected and composed of slatey clays and stony soils. The terraces are mostly covered by herbaceous vegetation and shrubbery. The floodplain is developed along the entire first section. It is mostly dry and covered with shrubs in some places. The floodplain is flooded by 2-3 days a year during spring floods. August 2011 Page 1

38 The river bed is moderately meandering and mostly unbranched. The river width varies between 4 and 32m, with depths of 0.3 to 2.4 m and flows of 1.4 m/sec to 3 m/sec. The second section of the river (from village Kekhvi to the confluence with the Mtkvari) is 42 km in length. The valley has a trapezium shape along this section. The valley slopes are terraced with terraces being used for agricultural purposes. The floodplain is well delineated; largely without vegetation and covered by water during 1-5 days a year in the course of spring floods. The river bed is moderately meandering and branching. The river width ranges from 4 m (village Shindisi) to 60 m (city of Gori), with depths from m to m and flows of m/sec. The river is recharged by precipitation, snow, glaciers and groundwater. It is characterised by spring floods and low water levels in winter. The river discharge is as follows by seasons: spring 30-39% of annual discharge, summer 37-42%, autumn 14-16% and winter 8-9%. The River Liakhvi is used for irrigation. Irrigation systems of Kehvi, Tiriponi, Saltvisi and Zeda Ru and numerous local canals supply irrigation water from the Liakhvi. A water reservoir was commissioned on the River Patara Liakhvi (left tributary of r. Didi Liakhvi) at village Zonkari in The reservoir is located at a distance of 31 km from the confluence. The reservoir was created by a ground dam (height 69 m, length 455 m). The reservoir length is 3.65 km, average width 0.38 km, average depth - 29 m. The total volume of the reservoir is 40.3 M m3, useful capacity - 39 M m 3. The reservoir provides irrigation water for 21 thousand ha of agricultural land in Shida Kartli. The source of the Patara Liakhvi is comprised of springs (altitude 2,680 m) north-west of Mount Chabarukhi (located on the western branch of the Lomisi ridge). The Patara Liakhvi flows into the Didi Liakhvi near village Shertuli. The river length up to the Zonkari dam is 32.5 km, with an average inclination of 50% and a water catchment area of 268 km 2. The 1991 earthquake posed a reservoir dam deformation risk; therefore, filling up the reservoir was avoided thereafter. Dam rehabilitation works were completed in 2002 when water diversion and irrigational tunnels were repaired. After this a recommendation was issued to fill up the reservoir with only 26 M m 3 water. Following the August 2008 hostilities, the reservoir sluices were shut. As a result, the water levels rose higher than normal in the reservoir. Due to ample precipitation in May-June 2011, water started to overflow through emergency tunnels and there was a real risk of dam failure. It is calculated that in the event of failure of the Zonkari reservoir dam, the maximum discharge would be 21,186 m 3 /sec near the proposed crossing point, which exceeds the maximum natural discharge of the Liakhvi by 19,426 m 3 /sec. Taking into consideration the terrain near the crossing, the majority of the water would overflow towards Mejuda valley located at lower elevations. Due to reinforcement of the banks of the Liakhvi near the existing crossing, the maximum predicted discharge in the event of dam failure would be 6,919 m 3 /sec, which would result in a predicted alluvial bed scour to a depth of 10m or down to the basic rock. August 2011 Page 2

39 Figure 1 Boulder barrier, existing WREP crossing, r. Liakhvi August 2011 Page 3

40 Section 3.2c River Supsa Report

41 Table of Contents 1 Introduction Field Survey Scope and Methods Brief Hydrological Description of River Supsa Brief Description of the Proposed Crossing... 2 Table of Figures Figure 1 Point P3 (next to a vehicle)... 3 Figure 2 Point P Figure 3 P1 collector view... 4 Figure 4 River Supsa view at the proposed crossing area... 4 August 2011 i

42 1 INTRODUCTION This report summarises the findings and observations made in the course of the hydrological survey of the proposed Supsa river crossing site (AM 372). The survey was conducted on 19-20th July, The team was composed of the following Dzelkva personnel: Baadur Ukleba, hydrologist, and Irakli Tandashvili, field assistant. 1.1 Field Survey Scope and Methods The hydrological field survey involved the surveyors walking 200m downstream and upstream of the proposed crossing and 100m wide strip on both banks of Supsa river around the proposed crossing. The survey areas were identical to those covered by baseline ecological surveys (i.e. botanical and zoological surveys). The survey was carried out as described in Section 3.1 of the E&S Baseline Report. 1.2 Brief Hydrological Description of River Supsa The source of the Supsa is located on the northern slopes of Ajara-Imereti ridge, at the altitude of 2,600 m above mean sea level (amsl) north-west of Mount Mepistskaro. It flows into the Black Sea near village Grigoleti. The total length of the river is 108 km with an average inclination of 24.1%. The total catchment area is 1130 km2 and the average altitude of the catchment is 970 m. In total, 790 tributaries flow into Supsa river; their total length is 1,428 km. The main tributaries are as follows: r. Baramidzetskali: length 21 km r. Gubazeuli: length 47 km r. Atsavra: length 12 km r. Bakhvistskali: length 42 km r. Shuti: length 12 km. The average density of the Supsa tributary system is 1.26 km/km2 and part of the Supsa basin (approximate length 85 km and width 13.3 km) is located in the western part of the northern slopes of Ajara-Trialeti ridge. The upper part of the river basin lies in mountainous terrain and the watershed altitudinal boundary of Ajara-Trialeti ridge is at 2,200 2,800 m. Narrow deep gorges and ravines are numerous in the upper reaches of the basin. Central and lower parts of the basin located on the southern slopes of Guria ridge and northern slopes of Nasakirali ridge are characterised by low mountainous terrain and relatively smooth shapes. The lowest part of the river basin is situated in the Kolkheti lowland where the Supsa valley is not clearly delineated. The geology of the upper reaches of the river basin is represented by tufogenes, quartz-grained sandstones and sandy-clayey slates. The remaining areas of the basin are represented by conglomerates and various types of clays with layers of marls, gravel and sand. The basic rocks are mainly overlaid by loamy soils. Alpine meadows are the most frequent vegetation types is the upper reaches of the river while vegetation is represented by mixed forests at altitudes below 2,000m. The majority of the central and lower parts of the river basin are used for agricultural purposes. Almost 70% of the river basin is covered by vegetation. August

43 The valley has a V-shape in the upper part of the basin. The floor width varies from m to m. The valley slopes are steep and dissected by narrow deep gorges of the tributaries where the valley slopes are mostly covered by loamy and clayey-loamy soils. There is no floodplain; the river bed is moderately meandering and unbranched. It is characterised by high inclination (approximately 55%). The river width fluctuates from 2 m to 20 m whilst the depth varies from 0.1m to 0.6m. The flow varies from m/sec to 2-3 m/sec. The bed floor is uneven, covered by boulders, pebbles and gravel. The river valley has a trapezium shape in the middle part; the valley floor is flat ranging from 1km to 4 km in width. The valley slopes, which join with slopes of adjacent ridges and hills, are low and gentle, merging with the river terraces. The terrace width ranges from 0.5 km to 3 km. Both river terraces and valley slopes are covered by loamy soils and are almost entirely used for corn crops. The river bed width is m at the estuary; the river banks (height m), which are comprised of loose strata, are collapsed and steep. The Supsa is a Black Sea coastal river characterised by flash floods caused by rains throughout the year. The average number of flash floods varies from 15 to 27 per year. The maximum numbers of flash floods are usually observed in the autumn. The river discharge is closely dependent on quantity and intensity of precipitation. The annual discharge is characterised by maximum events in spring and autumn. The spring maximum is usually observed in April, sometimes in May while the autumn one is usually observed in October. The discharge distribution by seasons is as follows: spring % of annual discharge, summer 18-25%, autumn 17-23% and winter %. The maximum volume of solid runoff is observed in April-May and October-November at hydropower station Khidmaghala. It reaches 10 kg/sec in each month. A maximum turbidity value of 8,200 g/m 3 was observed in the same location on 04/05/1954. Local residents use river for boating and fishing near the estuary. 1.3 Brief Description of the Proposed Crossing The proposed crossing area is located between AM 371 and AM 373. The new crossing is planned to be constructed by horizontal directional drilling (HDD); the start point of the HDD (P3; Coordinates: / ) is located on the right bank of the river at a distance of approximately 940 m from the river bed while the end point (P1; Coordinates: / ) is on the left bank at a distance of circa 550 m from the river bed. P3 (Coordinates: / ) is located approximately 125 m south of AM 371 on an earth mound between the old, now dry and disused, fishery ponds. The area is covered by wetland vegetation (Fig. 1). P2 (Coordinates: / ) is located ca 550 m south of P3, 125 m north of the Supsa-Grigoleti motorway on the area of the former fishery ponds, which is covered by wetland vegetation (Fig. 2). P1 (Coordinates: / ) is located on the left bank of Supsa river, circa 350 m north-east of Supsa terminal and 70 m north of a drainage collector. The area to the east is used as maize field while the areas to the west are not cultivated. The drainage collector should ensure diversion of surplus water from arable lands of villages Khidmaghala and Tskaltsminda. This collector is connected to the Chiri river (left tributary of the Supsa river). The collector length is 2 km up to P1, with a width of 6 m and depth of 2m. The collector floor is occupied by dense herbaceous vegetation and shrubs (Fig. 3). August

44 Figure 1 Point P3 (next to a vehicle) Figure 2 Point P2 August

45 Figure 3 P1 collector view The length of Supsa river from the source to the proposed crossing point is approximately 105 km and the water catchment basin is circa 1,125 km 2 in area. The river width is 80 m in the crossing area, with a depth of m and flow of circa 0.35 m/sec (Fig. 4). The river banks are comprised of loams and their height is m. The banks are covered by herbaceous vegetation with alders. Figure 4 River Supsa view at the proposed crossing area The average multi-year discharge is 48.5 m 3 /sec at the proposed crossing point and a maximum discharge with a 100-year return period is 1,230 m 3 /sec. The multi-year average of absolute minimum discharge is 12.7 m 3 /sec. It should be taken into account that the area where tunnelling is planned, like entire Kolkheti lowland, is characterised by high (shallow) groundwater level, which is at a depth of m from the surface. August