بررسی آسیب‌پذیری تپه‌های ماسه‌ای ساحل شرقی بندر جاسک با استفاده از مدل DVI

Introduction: Sand dunes throughout the world are under the influence of various natural and human pressures and very sensitive systems whose preservation needs a proper management. The importance of the role of coastal sand dunes is that they act as an obstacle to the waves, as well as the sand reservoir of the beach supply source against erosion. The main part of the eastern shore of Jask port is the sandy hills of the coastline. In the study area, the construction of new berths of Yekboni, Hijdan and Surgalm, made after 2006, as well as the clearance of hills to carry out such works as road construction and the development of settlements, as well as the absence of protective laws and management can increase vulnerability so vulnerability assessment can alert managers to increasing vulnerability due to exogenous or intrinsic changes and thus reduces the risk of environmental changes in the hills system.
The study area is located on the east coast of the port of Jask, and in the east of Hormozgan province, and Geographically the coastal belt situated between  57° '51 00" E to 57° 56' 26" E and 25° 40' 45" N to 25° 42' 50" N .
Methodology :In the first step the empirical relations between the checklist parameters and the dune vulnerability have been observed. In the second tier the value range for the quantitative variables have been documented on the basis of the available structured checklists .Partial vulnerability indices geomorphological condition (GC), marine influence (MI), aeolian influence (AI), vegetation condition (VC) and anthropogenic effects (AE) were calculated as the ratio between the summations of given variable ranks within each variable class (PVi) and the total maximum possible rank within the class (formula 1).
.(formula1) Pv=
A total DVI ( total Dune Vulnerability Index) was calculated as the average of the five partial vulnerability indices (PV) as per (formula 2 ).
.(formula 2 )DVI =∑PV / 5 = (GC +MI + AI +VC + AE) / 5
The protection measure index (PM) was calculated separately following the same formula of PV, summation of variables ranking within each variable class (PMi), expressed as a percentage of the total maximum possible rank within the class.
Lastly, the residual value as the difference between DVI and PM (DVI-PM) has been calculated to describe the stability of the dune system.
In the studies by Davis (1995) to calculate the vulnerability index, referred to as (VI) the calculation of the partial Vulnerability Index is not done, and the vulnerability score from the division of the total variables obtained from all the group of variables, based on the maximum total sum of the concessions of the entire group of variables, is obtained for each site.
Results and discussion: Among the investigated factors, the geomorphologic status of sand dunes, the factor of wind processes, has the highest impact and human factors, respectively, with the least impact on the vulnerability of hills. The characteristics of the sand dunes of the area, including low altitude (mostly less than 5 m), slopes over 30 degrees of their upstream slope, good to good alignment, increased the hills' vulnerability to natural factors.
The low percentage of vegetation on the side of the sea, as well as the low percentage of vegetation colony between the sand dunes and the maximum flow, as well as coastal changes that are due to the construction of docks and slopes in recent years It has been the cause of the high vulnerability of hills to wind processes.
The overall vulnerability rate (DVI) in areas number one, two, and three was 0.58, 0.53, and 51, respectively, and severe was evaluated. In two other areas, this value was less than 0.5 and the overall vulnerability was average.
The classification of the results for the DVI-PM index showed that the DVI-PM index obtained for all sites was more than 0.11 and requires quick management. The obtained equilibrium index shows that there is no balance between the sensitivity of the sites and the management measures to maintain them.
The comparison of the two methods for the calculation of vulnerability, the first method (DiaPangan, 2014) and the second method (Davis, 1995) shows that in both methods, the quantitative values obtained on site 1 are completely identical, but in other areas the slightest difference is a maximum of 0.2. Comparing the qualitative results obtained by the two methods, the vulnerability of the sites is the same except for the No. 2 site, which was severely vulnerable in the first method, but in the second method, the severity of the average vulnerability was assessed.
Conclusion: Among the investigated factors, the geomorphologic status of sand dunes, the factor of wind processes, has the highest impact and human factors, respectively, with the least impact on the vulnerability of hills..The overall vulnerability rate (DVI) in areas number one, two, and three was 0.58, 0.53, and 51, respectively, and severe was evaluated. In two other areas, this value was less than 0.5 and the overall vulnerability was average.