Site selection using GIS techniques Khoncheh dam site selection S. Khalil Aghili Engineering Geologist Isfahan Regional Water Company

kashan

Site location

Isfahan kashan Gavkhoni swamp

Goals: 1- Utilization of GIS as data bank and a tool for administration of spatial data, related to dam geological studies. 2- Exploitation of 3-dimensional tool of GIS in optimization of the reservoir area and volume. 3- Processing of landsat image in Geology. 4- Utilizing processed images in GIS media in drawing and bordering geological units.

Site Selection using GIS Technigues Khoncheh dam site selection Objective: In studying dam- sites, different fields of science are engaged. The first step to be taken is the need of building a dam, which according to reconnaissance studies, water resources are allocated and the area that needs the water is introduced. When hydrologists calculate the run- off in a water – shed basin, the first question would be; where along the river- course in the catchment area is suitable to build-up the dam? How high is the dam? What is the size and volume of the dam body? What about the topography of the dam surroundings? What is the extension and area of the reservoir with different dam heights? What is the capacity of the reservoir? What are the gradient of the slopes that form the reservoir walls?

(As we know, stability of slopes basically depend on Geology, ground water level and gradient of slopes) And finally where are the best places or axes along the river to perform feasibility studies? The most important objective of this paper is to show the use of GIS as a suitable tool to answering all of the above questions timewise and moneywise. It is quite understandable that answering all the mentioned questions in a classic approach has its own solutions. But in short – run, you are expected to have various layers of information for your hydrologist, meteorologist Hydrogeologist, land form expert, geologist and other experts very quickly and effectively. GIS or Geographic Information System can help in this relation.

Methodology : Khoncheh dam is located in central Iranian water shed area. In a smaller scale it is a part of Cham rud water shed. This basin is located between longitude of 51˚,01',57" to 51˚,21',40" and latitude of 33˚,40',30" to 33˚,58',28". For the first stage of reconnaissance the topograghic map was called by using Arc GIS and the boundry of intake area was marked. Then Hydrologist of the project was able to calculate the run off by using precipitation contours, Meteorological stations’ data and the area of intake.

By calling the Landsat image of the area through Arc GIS, geologist of the project was able to focus on land forms and trace the river – course. Based on previous site visits, it was possible to nominate a number of places as dam axes. Meanwhile the geological map of the area could be transformed onto the topographic map in order to correlate the data corresponding to geology and landform. When the two feasible axes of dam were marked on the topo map, dam heights and reservoir areas were calculated. All the tributaries meandering to the river course were marked and their related areas that could drain water into the reservoir were calculated. River course gradient was taken into account in order to consider sedimentation potential and probable slide and river- bed sudden meandering concerning faulting was examined as well. In khoncheh dam two dam site alternatives were chosen. Physical descriptions of the two sites are reviewed in detail below.

SITE NO.1 The up stream axis is called site No.1 As. you can see in the contour – topo landsat image, the river course runs from bottom to top of the image (south- North trend). The geological rocky formation is extened from east to the middle of the image, where it is dissected by the river. To the west, a vast area is covered by Quarternary fan deposits which, in turn cover the rocky formation of tertiary marl, shale and intrusive Dacite rocks.

SITE No.2 The downstream axis is called axis No.2, about some 900 meters downstrean of axis No.1 There exists a geologic outcrop of rocks, which according to site inspections is consisted of alternation of limestone and marly layers. Both left and right abutements are composed of limestone and marly layers. In addition there is a noteworthy tributary which joins the reservoir from left which according to hydrologic calculations has a potential of around one – million c.m. water added to the total volume of the reservoir.

CONCLUSION: Two dam axes were compared in this research and the downstream or axis No.2 was chosen for further phase-1 studies..

A constructed pond with geomembrane m3 capacity

Construction aims: Khoncheh dam ْGeographic Location Khoncheh dam is located in a distance of 24 Kms North west of kashan, near khoncheh village on Cham roud river X= Y= Z= Storing water to improve farming in dry seasons. Flood control before approaching the city of kashan. Developing agricultural related industries and enhancing occupations. * * *

Earthfill(clay core)Dam type 393 mDam crest length 44.5 mDam height (river bed) 700 km2 Water shed area 1366 m‍Crest Elev.(a.s.l.) 10.1 M.C.M.Reservoir capacity(N.W.L.) 1 M.C.M.Inactive capacity 7 M.C.M.Annual Regulating water 100 ha.Improving irrigation

Axis-1 Axis-2

Axis-1 Axis-2

Area Elevations

Utilizing TIN in calculating different reservoir volumes

Site Topography

Geological map of Area

Technical Specifications of Axis-1 cordinatesDam hightN.W.L. Dam body Volume Reservoir capacity X= ma.s.l m9 M.C.M Y=

Axis-1

Geotechnical drillings

Geotechnical Bore holes along Axis - 1 kf1 kf4 kf2

Axis - 2

Geotechnical Bore holes along Axis - 2

Axis - 1 Cut off wall Rock grouting

Axis - 2 Cut off wall Rock grouting

Flood course

Reservoir upstream view

Flood course and mountain forming dam right abutment

Axis-2

Outcrop of rock units

Oblique bore hole Left abutment

Axis – 1 top left side Axis – 2 bottom left side Facing towards upstream

Axis – 2 downstream gardens And alluvial terracess along the road

Axis – 2 downstream gardens And geologic setting on the river bank

Axis – 2 right bank elevations

Components of alluvial deposits

Alluvial debris

Quaternary River Terrace

Components of alluvial deposits

Irregularities in sedimentation and Sorting of gravels and pebbles along The river-bank terraces

Geological setting of sandstone & Marly units overlain by limestone

Vast flood course some 1000 meters Downstream of Axis - 2

High permeability(120lit/min)

High permeability(110lit/min ) High permeability(125lit/min )

High permeability(110lit/min )

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