Mapping of Salinity Hazards in Mond Region Using RS and GIS

Introduction

The data needed for prediction of geomorphologic degredation are generally derived from field observations, which are costly and time consuming. The use of remote sensing techniques can decrease the cost of data acquisition. Remote sensing can also provide up-to-date data for large areas in a short time compared to traditional methods. Remote sensing is rapidly becoming an important source of data and information for different researchers. It is clear that in the arid regions, soil salinity, water quality are the main problems in watershed management and development planning .The Mond river basin is one of the largest basins in the southern part of Iran (Bushehr province) which flows into the Persian Gulf near Khormuj city (about ۱۲۰ Km to the east of Bushehr city).The GIS database may also contain agricultural, socio-economic, communication, population and infrastructure data. This can be used, in conjunction with the flooding data. For an evacuation strategy, in conjunction with the flooding data, rehabilitation planning or damage assessment can be performed.   

Salt-affected soils have been identified as one of the three main limiting factors hampering crop production in this region of Iran۱:place>۱:country-region>. The widespread effects of salty springs and the saline parent materials of past ages are considered as the main cause in bringing the salts from lower strata up to the soil surface. Despite of various control measures this has resulted in a rapid expansion of salt-affected areas. Such a dynamic environment calls for up-to-date information regarding its extent and nature as pre-requisite for the sound management. Unfortunately, until present, this usually remains inadequate mainly due to the lack of an efficient assessment method. However, Satellite Remote Sensing (SRS) with higher spatial resolution is now available for this purpose (Singh and Dwivedi, ۱۹۸۹) which in combination with Geographic Information Systems (GIS) may yield more reliable results (Battle-Sales and Abad-Franch, ۱۹۹۲). In this context, the present study was carried out with the objectives (i) to develop a methodology for mapping the salt-affected soils using SRS and GIS, (ii) to assess the capability of GIS for comprehensive classification when interfaced with SRS data, and (iii) to interpret the salinity with respect to crop production.

Research question

The main research questions are as follow:          

۱- How is salinity distributed in the study area, in particular where the sources located are and are there spatial trends?

۲- Which sources of water are used by the farmers for agriculture purposes, and how do they deal with the salinity issue?

۳- Is it possible to relate land use changes with the spatial distribution of salinity?

To provide answers to the research questions stated a number of objectives have been formulated. The main objective is to map salinity distribution and water quality in the first part of the Mond river alluvial plain using field observations, RS data and GIS, to improve agricultural land management and human settlement planning.

Methods and Material

We had

۱.      To create a DEM of the study area. 

۲.      To create a flood map of the study area using a digital elevation model assuming the same water level as during the ۱۹۸۶ flood event.

۳.      To create a map of the study area

۴.      To compare the maps of the study area obtained by satellite images and the DEM.

۵.      To create a salinity map of the study area.

1. To create a geology map of the study area for predicting water quality of drainage and chemical quality of the rivers.

Hazelton (۱۹۹۱) provides a detailed discussion of hydrologic and pollution modelling using GIS.

The applications discussed above range from relatively simple local-scale hazard maps to national-scale risk management initiatives..

Study area

Mond۱:placename> River۱:placetype>۱:place> is one of the large rivers in Iran۱:place>۱:country-region>. The basin of this river is located in Fars۱:place> and Bushehr provinces (Longitude ۵۱° ۱۰¢   E to ۵۴° ۲۸¢ E and Latitude ۲۷° ۲۰¢ N to ۲۹° ۵۱¢ N). Its tributaries originate from the mountainous parts of these two provinces and join each other before discharging into Persian Gulf۱:place>. The area of this basin is about ۷۰۷۰۳ Sq.Km (about ۴۸۰۰۰ Sq.۲:givenname> Km۲:sn>۱:personname> is in Bushehr province and the study area is about   ۲۳۰۰ Sq. Km). This research focuses on the Mond sub basin.  The river in this region originates from the Samarkan۱:placename> Mountains۱:placetype>۱:place>, with ۸۰۰ m above sea level in average. The length of river is about ۶۵ Km, and the average slope of area is about ۱.۲ %. The general direction of the river is south – east to north – west. This basin has a high capability for agriculture development and the most important problem in this area is water resources restriction and soil salinity. The study area was studied before by JAMAB advisory Co.۱:place> and it is under study by other companies in order to find agricultural water resources possibilities and locations.

The climate is arid subtropical, with hot summers and mild winters. Relative humidity is low to very low during the whole year. The mean annual rainfall (period of ۶۳ years) in the region is ۲۵۰ - ۵۳۰ mm/year, ۹۰% of which falls during the months October to April۲:givenname> (during the winter months). The temperature reaches it maximum from mid-June to September. Average annual evaporation from a Class A pan is ۳۵۰۰ mm of which about ۳۵% - ۴۵% occurs from June۲:givenname> through September. As in most arid areas precipitation between years varies considerably.

Figure۱(Left) Situation of Mond catchment in southern part of Iran۱:place>۱:country-region>. (Right) Situation of subcatchments in Mond catchment

Darvishi plain is located in a valley, very prominent in the Mond basin further to the South. A relatively flat area with a thick alluvial fill, believed to be several hundreds of meters in thickness .It is surrounded by higher elevated regions, often formed in the Bakhtyari and Illam formation. Alluvial deposits in the floodplain consist predominantly of sands and gravels in the upper layers and are underlain by clays and evaporates. The upper layers are at least ۳۰-۴۰ m thick as can be concluded from the well logs of wells in the Darvishi plain. The alluvial deposits are underlain and bounded by Palaeozoic rocks to the east and Precambrian rocks to the west. Alluvial sediments were deposited in a braided stream environment, which results in a complex landscape with a chaotic structure and high spatial variability. In the multiple stream environments channel and over bank deposits are formed at very small distances and layering is strong and discontinuous.

Figure ۲ geological map of the study area.

The sedimentological setting of the Darvishi plain is one of high variation of sediments and topography over short distances. The patterns are not entirely chaotic though and a number of geomorphological units can be distinguished. Recent main channel deposits are very prominent in the landscape, while depressions can also be recognized. Aerial photographs show clear indications of channels, point bar like structures, with alternating bars, levees, spits and larger relatively flat areas, presumably small river accumulation terraces or extended river bars and depressions.

   Units were distinguished on the basis of a geomorphological interpretation of aerial photographs. Braided river deposits form the Mond floodplain, which leads to a very complex geomorphology. The geomorphology is not completely random and since the water table is close to the surface, the upper layers of sediments are most important. These top layers are visible on aerial photographs and geomorphological units are readily recognized. It is not always possible to distinguish the cause of different reflections on aerial photographs. They are caused by geomorphology, soil, vegetation coverage or absence, and human actions. Usually geomorphology, soil and vegetation are interrelated, except in areas where agricultural fields have been created. We will refer to the combination of natural factors that make cause distinct reflections in the aerial photographs as landscape elements. Landscape elements were distinguished using a combination of the sets of photos from different years and stereoscopic interpretation. Where only natural vegetation was present this could be done accurately, in agricultural fields, some signatures could be recognized and these were delineated.

The soils in the area have developed fresh alluvial sediments, some colluvial materials and reworked alluvial sediments. Texture of the parent materials ranges from gravels to clays. Gravels are found in the riverbed, old channels and in some alluvial fans, clay in former oxbow lakes and other depressions. Soils are young and apart from enrichment with secondary carbonates, gypsum and salts, little soil genesis has occurred. This enrichment resulted in soils with a relatively homogeneous high pH around the ۷- ۸.۴, typical for soils with a high CaCO ۳ content. Due to the dry climate organic matter production is low and its decomposition is slow rendering soils poor in organic material. The soils are strongly layered as a result of the braided stream conditions in which their parent material was deposited. Classification of the soils is mainly based on the texture of their parent material in the upper most layers and their topographic position. The topsoil controls most of the interaction with the atmosphere and although the classification does not give a complete description of all the layers important for plant growth, it does stratify the landscape in units, which have significance for the land use.

Based on the main objectives, soil salinity distribution, and water quality in the Mond river alluvial plain for improved agricultural land management and human planning, fieldwork activities and data acquisition was carried out between ۲۱/ Jul / ۲۰۰۲ and ۲۱ / Aug / ۲۰۰۲. The field activities were:

 Soil – Determining EC & pH for ۷۸ samples, which were taken from study area. In this case, based on the visual interpretation of ETM ۲۰۰۱ image, the study area was separated to ۱۰ sub regions for sampling. The soil samples were taken from ۰ - ۲۰ cm depth by auguring. The samples were carried to the laboratory and EC& pH were determined. Sample points and their values are given in table ۱and fig۵.                               

Table.۱ Analysed soil samples in  Mond region

کلید واژه ها: SalinityDevelopment NaturalHazards Mapping Mond RSandGIS دورسنجی و GIS سایر موارد