Owing to the variation of the geological composition of earth units in both of the Northeastern and Northwestern Coasts , storage means and methods differ in both of them. References show that inhabitants of the Northwestern Coast area have established rain water harvesting systems since the Roman Age whether in storing rain water in roman reservoirs or establishing olive, fig and grapes farms in the depressions and cultivating grains using rain water. Some references state that the prevailing conditions in the area were characterized by a precipitation rate much higher than the current rate for the Northwestern Coast represented a grains basket for the Ancient Roman Empire. This is evidenced by the existence of a large number of reservoirs, each one accommodates nearly 5000m 3 of surface flow water. Rain water harvesting systems in the area relies on the soil's nature and geomorphological qualities.
Rain water harvesting systems adopted in the northern coasts are affected by the type of soil, depth of the sector, topography prevalent in the region, in addition to the geological composition of the land sections.
a)- Areas affected with the presence of the Libyan Highland
They spread mainly in areas of the Northwestern Coast where rain water is divided into three major parts; the first part settles in the underground, the second is lost via evapotranspiration and the third runs in the form of runoff water. Precipitation behavior was studied after falling in Bagoush Area. The ratios found were as follows:
• Precipitation amount leaked into the underground is estimated with nearly 13%.
• Precipitation amount lost in evapotranspiration is almost 28%.
• Precipitation amount that runs as a runoff approaches 56%.
The geomorphological phenomena in the region helped the development of water and soil in the following manner:
• The highland is considered a water-shed area, while the Pedomenti Plain and the coastal plain (depressed areas) are considered accumulative basins for this water.
• The elevated areas intersect a number of narrow and deep valleys especially in the eastern part of the Northwestern Coast . All these valleys are located within the scope of proper precipitation.
• The narrowness of these valleys allows establishing the dikes that hinder water flow and helps the soil structure and water penetration into the underground.
• The depressed areas in the coastal plain is marked by existence of series of linear calcareous cliffs and helps the latter to keep rain water and prevent it from flowing into the Mediterranean.
• Existence of some depressions of limited areas helps accumulating water and micro residues together. An example of this would be some of the areas chosen for cultivating fruit, vegetables and grains.
b)- Areas Affected with spread of sand dunes
These areas exist in the Northeastern regions. Because of sand dunes prevalence in the coastal area, chances of flooding are scarce except in the valleys extending from the middle of Sinai to the Mediterranean like Al-Arish Valley .
4-1 Storing rain water in the soil sector
4-1-1 Water spreading system
This system is applied on a large scale in the Northwestern and Northeastern Coast in lands of crops and pastures to improve the plants water supply. This system is composed of three areas (figure 1):
a)- Precipitation Area
b)- Drainage Area
c)- Water Spreading Area
Precipitation and Drainage Areas form what is known as Water-shed area. Precipitation and Drainage Areas are left without any arrangements while contour furrowing, earth dikes, stone dikes, soil pitting and soil ripping or chiseling are made in the water spreading area. Repeating these operations benefit in using water spreading where they increase permeability, decrease the soil lost and intensify vegetation.
4-3-1-1 The Dikes
Dikes vary in terms of type and method of construction. There are earth dikes and calcareous dikes with its different types. While small earth dikes are established depending on experience of the Bedouins in the area, the large calcareous dikes are set with a technical help from the administrative authorities. Table 6 refers to number and total of dikes in the Egyptian North Coast .
Table 6 :
Number and Volume of Dikes in the Egyptian North Coast
The Dike Type |
Number |
Volume |
Earth Dike
Stone Dike
Cemented Dike |
-
17001
416 |
163096
990270
41214 |
Dikes are constructed based on contour maps and soil analyses. Fruit and crops are cultivated in areas behind the dikes. Dikes exist in North Sinai and West of Matrouh in the Northwestern Coast .
4-1-1-2 Contour Furrowing
Contour Furrows are more efficient in the following cases:
-
The areas that can not hold water resources amounts coming into them due to inclination or impermeability.
-
The areas of increasing productivity of fodders by increasing additional water supply that can be kept in the contour furrows.
-
The areas that have a particular shape in terms of inclination and whose topography takes specific contour models.
It is noted that in heavy soil of low permeability, most of water coming via high currents of surface flowing is lost away from the area that should be intensively vegetated. But after many years, as a result of increasing the leaf area to a certain limit, this area is capable of holding the water flowing into it. This method fits at different declination degrees and different soil qualities whether deep or of medium depth. Efficiency of that system reaches its climax in lands where declination reaches 10%. It should be noted in contour furrowing that they are capable of conserving all the streaming water. Some small dikes must also be established to convert water inside the contour furrows.
4-1-1-3 Soil Pitting
Soil Pitting can be described as disconnected contour furrows that are made by certain types of disk-shaped ploughs called decentralized disks. Pits in the shape of chess or any shape that suits the soil declivity can be made by the pitting instrument. Soil pitting is distinguished from contour furrowing with the following aspects:
• Low costing.
• Possibility of implementation by vision and local expertise (does not require survey works).
• Use in the lands that do not fit for contour furrowing.
• Modern machines following the tractors that do the pits in nonsolid lands.
This method may be useful if workmen are available. The pits may be made with the appropriate depth, volume and interface to catch the flowing water.
4-1-1-4 Soil ripping or Chiseling
Due to the heavy nature of soil in grazing lands, water absorption is slow. Hence, growth of the flourishing plants will be affected. It is useful under these circumstances to use machines for ripping the consolidated and hard layers on and under the soil surface because it leads to increasing penetration of moisture into the land surface and increases the plants productivity. This method may be used in case of difficulty of using contour furrowing and soil pitting as a result of increase of the runoff flow from the adjacent high areas. Runoff water does not result in huge damages in the lands that were ripped and chiseled particularly in moderate declivity or semi-flat areas.
Soil ripping or chiseling is adopted when the soil is dry (before the water flow). The machines shares should be 4-6 feet wide and pushed to the depth where the massive layer requires crashing. In case of delay till the first water current flow, this system should be implemented at the borders of the upper area that is marked by the traces of the water line. In case of manpower availability, that system can be made in the form of relatively surface clefts that will be re-filled with earth for fear of causing problems for animals.
4-1-2 Small Catchment Water Harvesting
This system involves establishing farms of limited areas relying on runoff water coming from large catchment areas. This model represents the system currently established in the Northwestern Coast in the form of Hateyat in which fig, grapes, olive, walnut are vegetated. The Bedouins practice that kind of cultivation for hundreds of years. The farmers chose the declined areas of deep soil to set up their farms. This type of farms covers 5000 acres in the Northwestern Coast and nearly 10000 acres in the Northeastern Coast .
Recently this system has been rationalized. The mathematical models were made for calculation of participating areas of precipitation and determining the cultivated area that may reach 3 hectares and that is cultivated with summer annuals or planted with fruit trees.
The operation of that system requires the following:
1- Contour maps for the areas of precipitation and utilization.
2- Soil studies for the area of utilization.
3- Good water distribution system in the area of utilization.
4- Development of the prediction mathematical model for determining dates for cultivating the area of utilization (to match the area).
5- Use of aerial photographs in determining more of these areas. This system can be applied in new places like Middle Sinai, Halayeb and Shalateen on the Red Sea .
4-1-3 Sand Dunes
The sand dunes cover most lands of the North Sinai governorate where nearly 120 thousand acres are vegetated with fruit trees (walnuts, olive, palm trees) in the sand dunes. This area depends on conserving rain water in the soil sector. The Bedouins plow the land after the effective irrigations to decrease water evaporation from the soil sector. Addition of fertilizers can precede the plowing operation.
4-1-4 Summer Crops
Watermelon is one of the key vegetables planted in the Egyptian North Coast . Deep soil of high water content (rain + runoff) is chosen in the North western Coast for the cultivation of watermelon. The Bedouins plow the land following the effective irrigations (number of plows reaches 6 plows per season). Watermelon seeds are soaked till Altalseen begins, then they are planted in a wet soil (10-15 cm far from the ground surface). The watermelon will grow without supplementary irrigation. Five thousand acres are planted in the summer season annually.
4-2 Storing Rain Water in Reservoirs
Rain water is stored in Roman reservoirs and concrete reservoirs.
4-2-1 Roman Reservoirs
This system is known for 2000 years and requires a special geological state. This case was found in most areas of the Northwestern Coast . Tens of Roman reservoirs are monitored and cleansed. It was found that they were established in good geometric methods and with large capacities amounting to 5000 m3 .
• Steps of Establishing Roman Reservoirs
Six steps must be taken to establish ground reservoirs:
a)- Selecting the location of the reservoir to establish a Roman reservoir. The following should be taken in consideration:
1- The reservoir is established in the declined point in relation to the surrounding area.
2- The crystallized rocky layer is 60-90 cm thick.
3- The crystallized rocky layer extends for an area of 80-120m.
4- Water harvesting area for the reservoir allows the easy surface water flow towards the reservoir.
b)- Establishing the reservoir's mouth.
The surface layer is removed from the pit, then the crystallized rocky layer is removed by manual instruments.
c)- Digging the reservoir underground.
After digging the reservoir's mouth in the crystallized rocky layer, the reservoir is dug in the limestone layer. 300-500m3 were excavated in this layer by workers.
d)- Lining the reservoir's wall and bottom.
The reservoir's wall and bottom are lined by cement to prevent water leaking.
e)- Building the reservoirs mouth.
The reservoirs mouth is built with stones and cement. A small basin is set up in the front of the reservoirs mouth to sediment undesired materials and prevent them from entering the reservoir. Two holes are made for every reservoir; the first should be on the side to allow water flow and the second should be from above and covered by an iron sheet to abstract water.
f)- Preparing the area in front of the reservoir
1- The soil is cleared from the stones and plants to facilitate water flow into the reservoir.
2- A v-shaped dike is constructed to direct the reservoir's water flow.
4-2-2 Concrete Reservoirs
Two types of concrete reservoirs are constructed in the North Coast .
a)- The Concrete Reservoirs Constructed in the Northwestern Coast
The concrete reservoirs are constructed in the Northwestern Coast by the local administrations for drinking water use. One reservoir of capacity ranging from 500-5000 m3 is built for every village. Reservoirs are selected in the declined area. They should be built above the surface layer with nearly 50cm and the reservoir's depth should not exceed 6 m3.
b)- The Concrete Reservoirs Constructed in the Northeastern Coast
Because of sand dunes and sandy soil dominance in the Northeastern Coast , the technique of constructing water reservoirs differs from the former technique. Earth reservoirs are called Harabat where the land surface of the reservoir's water harvesting area is treated to increase surface water flow coefficient in two ways. In the first method, the surface layer is covered with a 2-5 mm cement layer; while in the second the soil's surface layer is mixed with alluvium 15-25km/m2 . The alluvial amount relies on the type of the surface layer. The proper decline before treating the land surface ranges from 5 to 8 % and the treated area is 700-1000 m2 under a precipitation rate of 100-150 mm. The reservoir walls and roof are built with reinforced concrete. The reservoir's capacity is 50-100m3 with the dimensions: 2.5 deep, 4 m wide, 10m long. 3-4 holes are built in an opposite direction to the surface water flow.
4-3 Storing Rain Water in the Subterranean Layer
After rainfall, water is directed to the subterranean layer. It can be used in many ways. Rain water moves under the effect of gravity with nearly 20-75% of the total rain amount till it reaches the hard layer or sea water.
4-3-1 Sand Dunes
Fresh water floats over sea water in the area of coastal sands ( North Sinai , Bagoush, Al-Kasr). Water salinity reaches 1000 particles per million.
4-3-2 Cracked Limestone
These cracks exist in the limestone cliffs (Pleistocene Age) in the Coast areas where ground water floats over the saline sea water. Ground water salinity ranges 1000-2000 particles per million. These cliffs are separated by linear depressions covered by alluvial sediments mixed with gypsum. The cracked limestone which is considered an extension of the layer holding water is covered with sediments. Soil compositions in the depressions reflect the groundwater high salinity that exceeds 2000 particles per million.
4-3-3 Valleys Sediments
The layers holding water are under the Valley's main stream. Water exists in that composition either above the impermeable layers or above sea water. The main source charging these layers is seasonal winter precipitation.
4-3-4 Miocene Rocks
Miocene rocks were formed in sea, they usually reflect ground water high salinity that may be more than 4000 particles per million. Groundwater may surface in some locations in the form of perched water-table with salinity less than 1000 particles per million as in areas like Al-Dabaa and Ras-Al-Husan.
4-4 Methods of Groundwater Uses
4-4-1 Open Trenches
This form of groundwater appears in North Sinai and the Northwestern Coast . These trenches are established as open channels that are vertically excavated till depth of one meter under ground level. They are considered watershed and appears as an open canal after being filled with water.
4-4-2 Al-Mawasy System
This system is established in the areas between sand dunes heights where ground water is only one meter away from the ground level. In this case, a manual well of 1-1.5m can be dug. Various plants of fruit trees and vegetables can be grown under that system. In early stages, these plants can be irrigated by water from these surface wells and may later depend on the force of abstraction from groundwater near the ground level. Modern irrigation methods are recommended for increasing water use efficiency and rising productivity.
4-4-3 Canant
This system is constituted of a main horizontal pipe and a number of vertical pipes. Perched fresh water is accumulated through perforated vertical pipes. This system exists in the layers of sand soil.
4-4-4 Horizontal Wells
This system is applied in rock areas where the horizontal pipes penetrate the rocky layer in the slopes and reach the area holding ground water. Through the upper holes in the pipes, water is accumulated then extracted from the pipe mouth.
4-4-5 Manual Wells
That system is established in the areas of ground water accumulated from precipitation at a depth of 10-15m. The wells are dug by manpower. The well's opening is built with local stones, water can be abstracted from that well by machines or windmills.
4-4-6 Springs
A number of springs are located in the Egyptian Northwestern Coast where they are productive in winter. That water comes from watershed areas.
4-5 Strategy of Improving Water Harvesting
Total amount of rain water falling on the Egyptian North Coast reaches nearly 1.56 m 3 on an area of 14000km 2 (700km× 20km) with an average of 140 mm annually. No more than 1.756 million cubic meters of the aforementioned amount is annually stored in various types of reservoirs.
Table 7 illustrates the number of water reservoirs and its storing capacity in the Egyptian North Coast
Storage Forms |
Number |
Storage Capacity |
Old Roman Reservoirs
Roman System
Rocky Reservoirs
Concrete cemented Reservoirs |
2513
6141
70
1418 |
411400
1245427
7000
92170 |
Total |
10142 |
7189997 |
Comparing the figures implying the amount of rain falling and storage capacity, we notice the big difference considering the water amount lost from rain.
Therefore, there is a big chance for storing increasing amounts of the rain falling by developing and improving traditional methods and introducing modern storing methods. The other option that should not be neglected is raising efficiency of water storing in the soil sector by increasing maximal water holding capacity of the soil sector so that there would be a water supply from the soil to the plants for the longest time possible.
To improve water harvesting systems, integrated work system comprising the following elements should be taken into account:
1)- Introducing Geographic System for surveying the areas good for applying different water harvesting methods according to the nature of every area.
2)- Testing modern techniques of rain water storing (Plastic reservoirs- storing water in rocky areas after treatment..etc).
3)- Application of water harvesting methods and micro rain-fed farms.
4)- Improvement of storing rain water in sand lands like the Northeastern Coast and west of the Northwestern Coast (Brani-Al-Salum) by selecting soil treatment materials by coverage or chemical treatments to increase surface flow rate.
5)- Establishing modified water harvesting methods for some areas like area of Ras Al-Hekma in which runoff irrigation system can be established.
6)- Analysis of meteorological data and the land's topographic study and the soil composition to set the appropriate models for rain water harvesting.
7)- Establishing pilot farms for integrated agricultural activities under rain conditions.
8)- Determining safe abstraction from surface and medium deep wells particularly in the Northeastern Coast to prevent water and soil deterioration for salinity reached high values(3000 particles per million) in most wells.
9)- Determining areas of precipitation for every land reservoir, establishing the dikes suitable for directing the runoff water and treatment of the soil surface in the precipitation area.
10)- Cleaning and maintenance of open trenches and determining the cleanest area that can be irrigated at every trench.
11)- Raising the efficiency of measurement means for the runoff, rain falling, soil humidity and radical total.
12)- Introducing new and renewable energy like solar energy and wind power for water lifting to establish the farms under rainy conditions and water harvesting in the desert.
13)- Expansion in applying supplementary irrigation from different sources of which:
-Water transferred through irrigation channels.
- High-quality groundwater.
-Water stored by water harvesting methods.
-Water Desalinated from sea water or groundwater.
14)- Use of agricultural machines suitable for rainy areas starting from land preparation till harvest and constructing engineering works for rain water harvesting systems.
15)- Raising efficiency of use of water unit using soil amendments, soil coverage and application of soilless culture systems.
