Developing an USACE method to rehabilitate Hour-al-Azim marsh and dust management

Hour-al-Azim marsh is one of the most significant wetlands of the Mesopotamia watershed. In the past few years, severe environmental and hydrological stress have caused the loss of a large part of its area and its bed has become the largest focal point of haze in the southwestern of Iran. Determining delineation is one of the most important and necessary measures to protect a wetland’s ecosystem and, in this study, delineation was determined using the USACE-R-G method. This method is a combination of ecological and hydrological criteria with a Remote Sensing and Geographical Information System. The results showed that under the first scenario the marsh is about 3,279 km which about 882 square kilometers constitute free-water surface and its average depth is 2.4 meters. In the second scenario, these numbers were estimated to be 1,619 km with an average depth of 2.7 meters. Moreover, the area of the haze focus is about 1,659 km. As well as this, under these conditions the amount of water required to submerge the marsh is 7.9 in the first scenario and 4.4 billion cubic meters in the second one.


INTRODUCTION
() combined multispatial resolution imagery with GIS and field survey to delineate and map small wetlands in Kenya and Tanzania. Each country has its own set of rules to assess the delineation of wetlands, but the most popular of these methods is the US Army Corps of Engineers (USACE) method, in which hydrological, ecological and geological issues of wetlands are taken into account in identifying their bed size and limitation (Environmental Laboratory ). The US Environmental Protection Agency uses this method to calculate the boundary of wetlands in all geographic locations of the country, with any climate, in a way that all natural or man-made wetlands in the country follow this method (Schneider & Sprecher ).
In Iran, as in other countries, there are sets of rules on how to use surface water resources, and one of these laws is the Land and Coastal Law, which was passed in 1974.
According to this law, lands that are created as a result of sea water drop alongside any flow of seas, lakes, islands, The present study was undertaken to determine the wetland delineation in accordance with the laws governing the country to calculate dust zone area and the amount of water required to submerge it. Therefore, the USACE method in combination with RS and GIS (USACE-R-G method) was used to identify the boundary of the Hour-al-Azim marsh as well as to determine the dust zone areavolume. This method was used to evaluate the legal, ecological and hydrological border of the wetland. This study was conducted using field observations by researchers, RS, GIS, and hydrological, ecological and geological data.

Study area
Hour-al-Azim marsh, is one of the largest marshes in West Asia, located between Iran and Iraq. The eastern part of it, which is situated in Iran, is known as Hour-al-Azim while the western part is called Hur al-Hoveizeh, but international assemblies refer to it as Hour-al-Azim marsh. Hour-al-Azim marsh is bordered on the north by the Hour al-Sanaf and on the south by the main tributary of the Tigris River and its lowlands. This marsh extends latitude from 31 50 0 N to 31 0 0 N and also longitude from 47 58 0 E to 47 20 0 E. The length of the marsh from north to south is about 80 kilometers and its width is 30 kilometers. Inflow to the marsh is provided by the Karkheh and the tributaries of the Tigris River, known as Kahla and Mashah, as shown in Figure 1. The inflow to the marsh is also discharged through the Swaib and the Kassara channel.

Model development
In this study, the delineation of the marsh was checked using the USACE-R-G method, in which the delineation unification is based on three general principles of vegetation, soil texture and wetland hydrology. In the USACE-R-G method, two routine and comprehensive (Combination) methods have been proposed for estimating typical wetlands, and the routine method is divided into three levels of office, onsite and combination. In fact, the combination level is a composition of the onsite and the office level. Atypical wetlands are the ones that do not appear to maintain one of the three general principles of wetland designation due to human or nonhuman activities. In atypical conditions, portions of the marsh that were dried prior to legal determination are not part of the wetland's delineation ( Figure 2).
Hydrological, ecological and geological data of the study area are used in this study to verify the delineation of common marsh. Therefore, two scenarios were presented according to the USACE-R-G method to assess the delineation of bedrock marsh and its water storage capacity. These two scenarios are as follows:   As the marsh has been under stress and disturbance since 1981, hydrological data and satellite images prior to this year were used to determine the delineation in first and second scenarios (North portion).

Hydrology of marsh
According to the USACE-R-G method, the maximum rainfall, runoff, and average monthly discharge of inflows to the marsh prior to hydrological stress should be evaluated to obtain the year with the highest rainfall (wet year).

Rainfall
To determine the direct rainfall at the surface of the Hour-al-Azim normal rainfall data from synoptic stations and its adjacent rain gauges were used. The data related to the Basra, Al-Amara, Bostan, Abadan, Ahvaz, Mahshahr, Basra, Aghajari and rain gauge stations of Hamidieh, Abdulkhan and Molassani. After statistical tests, direct precipitation at the surface of Hour-al-Azim marsh were obtained using the IDW (Inverse Distance Weighting) method. In this method, by using IDW at the data stations, precipitation is obtained in the non-data areas. In this case, the value and weight of the station closest to the area is higher than at the other stations.
In general, the missing precipitation calculation P x equation using the IDW method is as follows (Ward et al. ): where P i is the amount of precipitation at the stations studied, W i is the square of the distance of the stations from the points with unknown precipitation P x obtained from the following equations: D x and D y are distance of stations from unknown points.

Input flow to marsh
As marsh flow is provided from the Karkheh and Tigris watershed, it was necessary to evaluate the normal discharge of these two rivers before environmental and hydrological stress, as well as inlet discharge after the occurrence of  Organization, the plant diversity of the study area was acquired.
In general, the NDVI is used to determine the dispersal, vegetation area, and free-water surface area of a wetland.
This index is obtained by analyzing satellite images. The NDVI index was obtained in terms of the two near-infrared bands, the red band of satellite images based on the following equation (Lasaponara & Masini ): where NIR: the reflectance from the near-infrared and RED: the reflectance from the red visible band. This index has values from À1 to 1 as presented in Table 1.
After identification of vegetation area and free-water surface using a 1:25,000 map of the study area and elevation points from marsh bed, the delineation of the marsh was obtained under two scenarios.

Direct precipitation at the surface of wetlands
The results showed that the maximum amount of direct rainfall in the study area was in January and was about 42 mm and minimum precipitation was in June to September and was less than 0.3 mm. Total direct rainfall in the wetlands was about 204 mm/year which brought about 650 million cubic meters of water directly into the marsh. These values are presented as monthly in Figure 4.

Surface flows
By analyzing hydrometric stations data of Hamidiyeh and downstream of the Kut barrage, it was found that the average inflow to the wetlands from Karkheh River, before the hydrological stress, was about 161 m 3 /s, which is about 59 m 3 /s after hydrological stress as shown in Figure 5. This means that the inflow to the marsh from the Karkheh River has been reduced to 40% of the initial flow. The average annual  the Tigris River has also been cut in half. These results are illustrated in Figure 6. Also, the maximum recorded discharge in these stations during the 1970s was in 1972. It can be inferred from the data presented in Figures 7 and 8 that this year is the wet year of the decade.

Soil texture
Based on Aqrawi's or Evan's studies (1993a, 1993b, ), it was found that the soil texture of the marsh consists of three layers. The first layer, which is about 7 cm thick, contains plant residues, and its color is black and in some places olive-gray. The second layer is silty clay soil texture with a thickness of about 30 cm and after this 30 cm layer, the clay content increases sharply and the soil texture becomes clayey silty. Because of the soil texture triangle, these soils contain at least 40% clay, soils considered to be impermeable, so that water permeability was neglected in the marsh.

Marsh vegetation
By analyzing Landsat satellite images between 1972 and 1980, the NDVI index of the wetlands was obtained. The index showed that, on average, 64 percent of the marsh area had vegetation, which decreased from north to south.
In the northern part, the highest density is present in the marsh, and Figure 9 shows the changes in vegetation and free-water area over the years. As well as this, according to     depths, so that about 60% of the marsh has depths of À1 to 3 meters as presented in Table 3 and Figure 11. In general, the average depth of marsh was 2.4 m. It was also found that the slope of the marsh in the northern part was steeper than the southern parts; beside this, the slope was from northeast to southwest, indicating that the inflow into the marsh, either from Karkheh or the Kahla and Mushhash rivers,    would initially drown the Hur al-Hoveizeh or then lead to a massive submergence in Hour-al-Azim.

Delineation in the second scenario
In this case, the marsh fell into the category of special wetlands such that, according to the UCACE method, dry areas of marsh are not recognized as a limitation. Thus, the Hour-al-Azim area was approximately 1,619 square kilometers; Figure 12 shows the current delineation of the wetlands. Also, about 37% of the marsh had a maximum depth of 2 meters as presented in Table 4. In general, the average depth of the marsh was about 2.7 meters. In this case, 4.4 billion cubic meters of water are needed to submerge the northern part of the marsh and, given that up to

CONCLUSION
In this research, we tried to delineate the Hour-al-Azim marsh using the USACE-R-G method as well as determine dust zone area. For this purpose, two scenarios were con-

DATA AVAILABILITY STATEMENT
All relevant data are included in the paper or its Supplementary Information.