مدل‌سازي مكاني مناطق تغذيه آبخوان‌هاي كارستي با استفاده از مدل KARSTLOP (مطالعه موردي: آبخوان كارستي خورين)

Spatial modeling of the areas charging karstic aquifers using KARSTLOP model, case study: Khurin Karstic Aquifer

به علت ماهيت پيچيده مناطق كارستي، مبحث تغذيه در آبخوان‌هاي كارستي امري پيچيده بوده و تعريف تغذيه در شرايط مطلق امكان‌پذير نيست. مناطق تغذيه، ميزان و توزيع فضايي تغذيه در آبخوان‌هاي كارستي، بستگي به عواملي چون ژيومورفولوژي كارست و ميزان توسعه آن، اقليم، شيب، پوشش گياهي، خاك و عوامل زمين‌شناسي دارد. آبخوان كارستي خورين در استان كرمانشاه، نقش مهمي در شكل‌گيري و استمرار حيات جوامع انساني اطراف خود و اكوسيستم تالاب هشيلان دارد. هدف از پژوهش، مدل‌سازي مناطق تغذيه آبخوان خورين با استفاده از مدل KARSTLOP مي‌باشد. بررسي نقشه پهنه‌بندي آبخوان خورين نشان مي‌دهد كه 61% از مساحت آبخوان داراي ميزان تغذيه بيش از 70% بوده و 88% از مساحت آبخوان، داراي تغذيه بيش از 50% مي‌باشد. اين امر حاكي از ميزان نفوذپذيري بالاي آبخوان خورين است. تطابق نقشه پهنه‌بندي نهايي با نقشه ژيومورفولوژي كارست سطحي آبخوان، حاكي از نقش اصلي ژيومورفولوژي كارست در توزيع مكاني مقادير تغذيه در آبخوان خورين مي‌باشد. مناطق با ميزان تغذيه بيش از 70% منطبق بر نواحي توسعه‌يافته كارستي راس كوهستان مي‌باشد. ضخامت كم خاك، پوشش گياهي نسبتاً تنك، تكتونيزه بودن منطقه، رخنمون سازند كربناته بيستون از ديگر عوامل موثر در ميزان تغذيه بالاي كوه خورين مي‌باشند. بالا بودن ميزان تغذيه و توزيع مكاني مناطق تغذيه آبخوان نشان مي‌دهد كه آبخوان در برابر انتشار آلودگي آسيب‌پذير بوده و نيازمند برنامه‌هاي حفاظتي و مديريتي جهت آلودگي با مدنظر قرار دادن نقشه پهنه‌بندي تغذيه و نقشه ژيومورفولوژي كارست سطحي مي‌باشد.

Introduction One reason for the importance of karstic areas is their important water resources. In general, the karstic aquifers have three areas: feeding, transfer and discharge. Recognizing of the feeding areas in the karstic aquifers has a key role in identifying of the hydrodynamic and hydrochemical characteristics of the aquifers as well as scientific and efficient management and utilization of them. The Karstic water resources are the main source for water supply in the Kermanshah province. The Khurin Karstic aquifer with an annual capacity of more than 24 m3, feeds the Hashilan pond. Besides, the local communities utilize this aquifer for drinking and agricultural water. Therefore, due to the important role of Khurin karstic aquifer in the supplying water of its surrounding local communities, modeling and recognizing of its feeding areas to quantitative and qualitative optimal management, identifying pollution, aquifer vulnerability and risk assessment has an important role in optimal and scientific management of the aquifer. The aim of this study is to model the Khurin aquifer recharge areas using KARSTLOP model. Methodology This study is a developmental- applied research which is based on library, field and KARSTLOP modeling methods. During the field investigations the surface karstic geomorphology of the area was identified. The Fillsink method was used to identify the karstic sinkholes and its results compared with field samplings. The name of KARSTLOP model is the abbreviation of eight parameters as follow: K: karstification, A: atmospheric condition, R: runoff, S: slope, T: tectonic, L: lithology, O: over layer, and P: plant vegetation. Field investigations were done to identify surface karstic geomorphology and recording the landform positions. Finally obtained zoning from the KARSTLOP model compared with the Khurin mountain geomorphology in order to evaluate the effect of the karstic landforms on the karstic aquifer feeding. The AqQA software to calculate the Khurin aquifer type, the PHREEQC software to calculate the saturation ratio, the Coreldraw X6 software to plotting the geomorphological map, and the ArcGIS 10.2 software to model the aquifer was used. Results and discussion Charging type of the study aquifer is autogenic. The maximum and minimum discharge of the study springs observes in May and in September, respectively. Usually, the electrical conductivity of karstic springs is less than 500 (?S /cm). The EC value of the study springs is less than 376 (?S/ cm). Among the anions, the bicarbonate ions are dominant in the springs and the spring water type is Ca-Mg-HCO3 bicarbonate. In terms of the present cations, calcium is dominant cation and followed with magnesium. The spring water has calsitic and magnesic facies. The spring anion succession is as follow: . The Piper diagram of the study springs is indicative of bicarbonate type and high amount of the bivalent basics of calcium - magnesium in the spring water, confirming the carstic origin of the study springs, as well as supplies their water from the carbonaceous altitudes of the surrounding area. Increase of the Mg concentration or decrease of the Ca/Mg Molar ratio is indicative of a long residence time of water in the aquifer and represents the lithology of the spring feeding formation. This value is more than 3.2 in the study springs. This suggests a short residence time of water in the aquifer and reflects the presence of the limestone in the springs feeding area. KARSTLOP model Eight parameters including K: karstification, A: atmospheric condition, R: runoff, S: slope, T: tectonic, L: lithology, O: over layer, P: plant vegetation are involved in the model. By studying above mentioned parameters and calculating their amounts, the final map of the aquifer feeding was prepared using equation (1). The feeding final map shows the spatial distribution of mean annual feeding (charging, Rch) and the feeding amount is expressed by (%). Equation 1: Rch= 4× K+A+4× R+ 2× S+T+4× L+3× O+P Surveying the charging final map and karst surface geomorphology shows that the obtained annual charge for the Khurin karstic aquifer ranged from 40 to 86%. In other words, based on the 8 parameters, 40 to 86% of the annual precipitation is saved through the aquifer feeding and the rest is out of reach. The maximum amount of feeding is occurred in areas with more than 80% charge, which are coincident with the flat surface of the Plzhh having devlin. While, the minimum amounts, 40 to 45% and 45 to 50% are occurred in alluvial plains. Conclusion KARSTLOP model is provided to zoning the prone areas to recharge in the karstic areas. The Khurin Mountain is situated in High Zagros and due to the presence of favorable condition for carstification, the karstic geomorphology is well developed in the study area. Study of hydrochemical characteristics of exiting springs of the Khurin aquifer shows their karstic origin, as well as the springs have bicarbonate water type. The feeder formations of the springs based on the Ca/Mg ratio are limestone formation. The feeding type of the Khurin aquifer is autogenic and type of landforms caused to create two types of feeding in the aquifer, they are concentrated and distributed. Obviously, in areas with concentrated feeding, most of the entering water consumes by feed aquifers. The Khurin final zoning map, in terms of aquifer recharge shows that 61% of the aquifer area has the charging amount more than 70% and 88% of aquifer area has the charging amount more than 50% This reflects the high permeability of the Khurin aquifer. Surveying the final zoning map resulted from KARSTLOP model and its correlation with the geomorphological map of the region, indicates the main role of Khurin mountain karst geomorphology in the spatial distribution of the charge amounts and the high values of the aquifer charge, which shows that aquifer is very vulnerable to pollution. because in the top of the mountain, due to the dominance of concentrated penetration and developed surface karstic geomorphology the contamination dissemination is pointwise and very fast, so it needs protection and management plans related to discussion pertaining to pollution together with considering the charging and feeding zoning map as well as the map of surface karstic geomorphology.