Unit Response Approach for Priority Determination of Flood Source Areas

J. Hydrologic Engrg., Volume 10, Issue 4, pp. 270-277 (July/August 2005)

Bahram Saghafian1 and Mohammad Khosroshahi2

1Research Hydrologist, Soil Conservation and Watershed Management Research Institute, P.O. Box 13445-1136, Tehran, Iran (corresponding author). E-mail: saghafian@scwmri.ac.ir
2Research Geographer, Research Institute of Forest and Rangeland, P.O. Box 13185-116, Tehran, Iran. E-mail: khosro@rifr-ac.org
(Accepted 8 June 2004)

Flood damages are usually concentrated along certain reaches of the main watercourse. However, a successful flood-control project must look beyond the damaged reaches by studying the contribution of headwater subwatersheds to the flood magnitude at downstream locations. Flood-control measures may then be initially planned in identified flood tributary areas of the watershed that strongly affect the flood peak at downstream river reaches. A simple iterative simulation technique is introduced, whereby the contribution of each subwatershed unit or group of subwatershed units to the flood peak response can be disaggregated. A flood index may then be assigned to each contributing unit to determine the change in response of outlet flood discharge caused by removal of that unit. The technique is similar to the unit response approach in groundwater studies. The proposed technique is applied to a watershed; and the effect of such different factors as design return period, storm duration, and size of the contributing subunits are examined. The interpretation of results is based particularly on the flood index corresponding to the contribution at the outlet per unit area of subwatersheds. For the watershed under study, the flood index analysis showed that while the differences in the contribution of subwatershed units may be salient for up to 100-year return periods, the contribution per unit area is expected to converge for rare floods. Moreover, subwatershed units that have larger area or that are nearer to the outlet may not necessarily generate higher flood contributions.

©2005 ASCE
doi:10.1061/(ASCE)1084-0699(2005)10:4(270)
Additional Information

Desert control methods in Iran

Stabilizing the shifting sand dunes Methods in Iran are:

•Biochemical method
•Biomechanical method
•Biological method



•Biochemical method
In this method, the first spraying the petroleum is used for stabilizing the shifting sand dunes by the tanks that are equipped with strong pumps,

•For seeding, Before spraying petroleum mulch we should seed near to raining season and then create a suitable cover on seeds.
•For seedling, we can do planting before and after spraying mulch. The selective trees should be compatible with ecological conditions.


Characteristics of petroleum mulch:

1) For the agriculture production should be harmless.2) Don’t injure hygienic the persons that spray petroleum mulch.3) Don’t remain unfavorable effects during ploughing and mixing the mulch and soil.4) Don’t have the unfavorable smell.5) Prevent from cracking the land and accelerate the sprouting.6) The air and rain can penetrate into it.





Biomechanical method

In this method, With creation of wind breaks on sand dunes and planting of seedling, prevent from shifting sand dunes and theirs detriments

Biological Method

In this method, The plants for plantation of seedlings are produced in stations of shifting sand dunes stabilization. These trees are sowed in mentioned regions in winter or at first are grown in plastic vases and then are transferred to original lands. Seeding is one of actions for stabilizing the shifting sand dunes. Yearly a lots of seed are gathered from artificial forests in desert .They are showed in another areas, suit helps to develop the vegetation covers in another regions.

Combating desertification objectives

•Protection of environment

•Stabilization of shifting sand dunes
•Protection and rehabilitation of farm lands
•Conservation of water resources
•Protection of roads and communication networks
•Sustainable reclamation of human settlements

Causes of desertification in Iran

Some causes of desertification in Iran are:

•Population growth:
The population of the country has doubled during the last 20 years and naturally the demand for agricultural and animal products have been increased proportionally to the rate of increase. Thus people were forced to increase the number of their livestock and to use the lands more extensively. In order to increase the area of agricultural lands, people converted the rangelands and forests into farms and croplands. They also cultivated marginal lands for rainfed crops without any consideration of their inherent potentials. These activities in many cases have resulted in desertification.

•Increase in the number of livestock:
Increasing demand for dairy products during recent years has caused the increase in the number of livestock. In addition to overgrazing due to excessive livestock numbers, most of the rangelands experienced untimely grazing in the forms of early grazing or late grazing

•Converting forests &rangelands into farmlands and increase of dry farming:
In the last decades extensive areas of rangelands located on the mountainous regions and steep slopes plowed and converted to the croplands and dry farming as the demand for cereals had increased. Since these kind of lands was not suitable for the agricultural practices soon after changed to a degraded land with very low productivity. Finally because of low productivity the land were abandoned and led to desetification processes




•Uncontrolled use of agricultural machinery:
Villagers and farmers can now obtain farm machinery easily. Most of these imported equipment do not fit the conditions of arid and semi-arid lands of Iran. These machinery not only let them much more extensive operations than traditional ones, but also are used to plow more rangelands and to cut more trees and bushes from the rangelands and forests.




•Fuelwood gathering:
Despite the fact that Islamic Republic of Iran is a rich country in oil well and oil industry, just a little portion of the villagers were able to use petroleum fuel before the Islamic revolution in 1979. In addition to the demand for fuel to meet household cooking and heating needs. In addition to the traditional fuel gathering some factories are also using fuelwoods.




•Refugees settlement:
During civil var. in Afghanistan both when Taliban governed and also during conflict between former Soviet and Mojahedin, many Afghan people left their country and settled in Iran and Pakistan as refugee. In Iran most of these refugees settled in the eastern part of Iran particularly in Khorasan and Systan Provinces. Excessive pressure exerted on land due to refugees activities to meet their requirement and demand for fuelwood caused more than 1.2 million hectares of lands being degraded.




•Overexploitation of water table and mismanagement of irrigation:
Overexploitation of ground water reserves for expansion of agricultural lands caused water table to drop to a critical level almost in the whole central plateau. As drought years persist, ground water table increasingly reused by stakeholders to meet their requirements in terms of irrigation and other needs. Since water table is not replenished in drought periods, thus resulted in aquifer deterioration and leads to land abundance. These processes finally resulted in desertification.

Features in Desert Areas of Iran

•Sand accumulation and formation of sand dunes are important features in inland and coastal deserts, which are considered critical problems. There are presently about 26 large-scale ergs, which have covered 120,000 square kilometers of deserts in Iran. It is noteworthy that the most important citadel of the world (Lout) is located in Iranian desert with pyramids of more than 500 meters height. Totally, Iran covers 5 million hectares of active sand dunes.



Nebka

•Nebkas are formed where wind erosion persists. It includes regions where sediments gathered around bushes. In this case, bushes gradually go upward until roots are disconnected from underground water and bushes will die.

(Nebka, yazd-Iran)

Kalout and Yardang:

Another feature in desertified lands is Kalout and Yardang formation which is formed by wind and water erosions. Strong and lengthy raining causes the degradation of lands exposed to erosion and so soil particles will being removed and form Kalout and Yardang hills.

(Kalout, China-Cansu Province)

Salty and Clay Pans:

•These features could be seen in central lower areas (playas). The percentage of salt in these spots is very high which doesn’t let plant establish easily. These spots are barren, without any vegetation. A large portion of central Iran is covered by this phenomenon.

Dr.Mohammad , khosroshahi (Salty Kavir, Qom-Iran)

Deserts of Iran

Aristida pennata is a good species that growth well on sand dunes


Dr. Mohammad,Khosroshahi between the
two Aristida pennata on the sand dune hills (Nieshaboor,Iran)

Desert of Iran:

The word “desert” illustrates an ecosystem with special conditions. Factors such as climatic criteria as well as soil criteria including geology, geomorphology, and soil and also the vegetation and ecology play a role in formation of deserts and particularly in Iran.

•In Iran, there are two main groups deserts: coastal deserts and inland deserts,
•Coastal deserts extend in a west-east strip, alongside the Sea of Oman and the Persian Gulf. humid winds in these deserts, have been their main distinguishing factors from inland deserts.
•The inland deserts are located in the center, east and south east of Iran, Lout desert is one of the most famous in this group, and second, is Dashte Kavir. These deserts have a surface area of 34 million hectares.

Lecture in training course in Gansu Desert Control Research Institute- China,Wuwei

A Glance of desert /desertification and combating desertification in Iran
GDCRI, Agu-Sep,2004
Dr. Mohammad, khosroshahi , khosro@rifr-ac.ir
Research Institute of Forests and Rangelands ,Tehran- Iran



Climatology:

•Numerous mountains and vast plains have given rise to various ecological attributes in Iran. Because of this complex climate Iran is famed for having four distinct seasons at the same time. It is mild and wet in the north, cold and dry in the west, mild and dry to hot and dry in central regions; and hot in the south. Annual precipitation in desert regions is about 50 mm, while it is more than 2000 mm in some part of northern region.


Vegetation of Deserts:

In deserts of Iran there are more than 44 families of desert plants with different varieties and kinds, which survive through unsuitable ecological conditions; and further play an outstanding role in preservation of soil and water in deserts. Compositae and Chenopodiaceae are the most important families of the desert flora.


kinds of plants for reclamation of vegetation and combating wind erosion and for stabilization of shifting sand dunes.

•Haloxylon ammodendrom
•Haloxylon persicum
•Haloxylon aphyllum
•Atriplex lentiformis
•Atriplex halimus
•Atriplex canesence
•Acacia arabica
•Acacia modesta
•Calligonum turkestanicum
•Calligonum leucocladum
•Panicum miliaceum
•Panicum axtisotal
•Tamarix romossima
•Tamarix stricta
•Tamarix aphylla
•Eucalyptus Sp.
•Prosopis Sp.
•Aristida sp.