Groundwater and the most important water problems in Yemen



Yemen is generally rely on surface and groundwater resources as a key resource for life, despite the fact that Yemenis were looking for water for thousands of years, especially in the era of ancient civilizations (SABA), when Yemenis built the first dam in history, namely (Marib Dam) and the accompanying creation of relatively advanced irrigation systems and water resources in Yemen is one of the traditional sources include rain (superficial resource) and the united groundwater (groundwater resource) and the total current water resources estimated at about (5200 million / m3) consumes them (256 million / m3) for agriculture and (25,200 million / m3) for drinking and household needs. And about (800 million / m3) for the purposes of the industry.

Yemeni Studies show that the southern parts of Yemen is the poorest hydraulically from the northern parts due to lack of rain and high temperatures, and the need for water increases as the population grew, leading to water shortage or malfunction of the water induction at about (10,800 million / m3) And the consequent decrease in the per capita amount of water (365 m 3 / year).

Every water studies on this subject, especially in the northern parts of it confirms that there is water problems facing this country in the near future and one of those studies carried out by all of the:

Bontez 1912 and the German group (58–35) and Consult (71–37) ITAL, and the German Mission (77) And the Dutch Mission (78) and the Swiss Mission (78) and Aryani (79–86) and Shaban (82) and al Ahdal (89) and Sufian (90) and there are other studies on the tanks in Aden carried out by Mahiser and others.

And water needs in the future will increase and per capita will drop at a rate 10 times higher than it is at the present time Which would be per capita in 2025 about 140 m3 and 47 m3 in 2063.

As it is clarified in the following table:

Per capita M 3 / year	population Million people	total water resources billion m 3	Water Resource Billion m3 / year	Year (AD)
473	11	5.2	3.8 surfacewater 4.1 groundwater	1990
325	19	=	=	2000
140	37	=	=	2025
47	110	=	=	2063

Terrain data and its impact on the water in Yemen:

1. in the territory of the southern highlands, which includes all of the provinces of Taiz and Ibb and part of Lahj, the precipitation rate ranges between 300–1000m.The total area of agriculture is almost 600 thousand hectares, The flat lands of this region is considered Basin rain fed (Catchment zone), which feeds by seasonal floods each of the Tuban valley and part of the valley of Banna on the south coast, also it nourishes Moazee, and Resian, and Nakle valleys and parts of the valley of Zabid on the western plain.
2. The central highlands province includes all of the territory of the Al beida governorate and Dhamar, and part of Sana'a governorate, the agricultural land area is about 650 thousand hectares, The flat lands of this region Basin rain fed which feeds by seasonal floods the valley of Banna on the southern coastal plain, and also feeds the valleys of Zabid and Rmaa and Siham on the west coast and also the valleys of Marib, Bijan and Hreib on a plain eastern plateau.
3. in the territory of the northern hills, includes land province of Saada, Hajja, Al-Mahwit and the rest of Sanaa province, with an annual precipitation rate of 300–600 mm, flat land of this region is considered the Basin rain fed which feeds by seasonal floods the cliff Valley that runs through the plain desert plateau, as well as the valleys of Srdod, Moore and Harrad on the western coastal plain.
4. in the territory of the desert plateau and it is in the foothills of the central and northern highlands of the eastern side until the Sultanate of Oman as well as areas (Saada / Al Jawf / Shabwa / Hadramawt / almahra) and the average annual precipitation rate among (50–100m), as the size of seasonal floods reaching the valleys as follows:

– Valley of Banna and Rcian 9–10 million / m3 Approximately.

– Valley Tehama 150 million / m3.

– Valley Marib 15 thousand / km3.

– Valley Moore 237 million / m3.

5. Central lowlands region includes lowlands of (Saada, Amran and Sana'a, Dhamar and Maeer, Radaa, Yarim and Aljond (from al Qaeda until Lahij), which most of the agricultural areas rely on groundwater in irrigation as is the case in Qaa Alioune (North of Amran) and the Alhakel Qaa in the South of Yarim and Qaa al Jhran in Dhamar and Qaa Radaa (albaedaa).
6. Al Rub Al Khali desert region is only sand dunes north of the plateau of Hadramout and east of interior plateaus extend to dozens of kilometers where water and sink into the sand.

Climatic characteristics and their impact on the amount of water:

It is known that most parts of Yemen are within the hot orbital region, which leads to a rise in temperature in Yemen, a consequent in heavy summer rains affected as a result of Yemen tropical low pressure. Where the highest level of rainfall in some areas of the province of Ibb (precipitation rate exceeds 800 mm / year then Mahaweet 600 mm / year) and thus decreasing precipitation even of less than 50 mm per year in the desert areas,part of the rain feeds groundwater during infiltration of to underground and other evaporates due to solar energy and the other part in agriculture and part flows into the valleys,and the estimated amount of annual rainfall on Yemen (65 billion / m3) and most of them go back to the atmosphere on the first day and the next few days of rainfall due to high evaporation rates and the resulting product nature of the arid climate that prevails in most of areas of Yemen along the year (Bamatraf et al. 1996), the rate of flooding in the valleys amounts (2–25 billion / m 3) up to (54 %) Of rainfall Any remaining of the water, for the reasons mentioned above.

The irregular rainfall in highland areas and scarce rainfall in the rest of the territory of Yemen has made intensive sustainable agriculture difficult.

Therefore, Yemen is one of the groundwater semi-arid areas (Ustic) which rain is the main source of water that feeds the aquifers and springs and valleys because the rainy season concentrated only in the range of (4–5 months) while becoming (7–8 months) in the case of drought, most farmers depends directly on rainwater in the mountainous highland areas such as (Eb / Mahaweet / Sanaa / Dhamar / Taiz / Haja), and indirectly in the coastal and eastern regions such as (Tehama / Marib / Shabwa / Al Jawf / Abyan) by plains formed from rainfall on mountain heights.

The total arable land (53 million hectares) planted (1.35 million hectares), (1.2 %) of which (1.02 million hectares) depends on rainfall rate (83 %) and 33 thousand hectares depends on irrigation (17 %).

It was found that the amount of water drawn from the valleys estimated (1060 million / m3) and covers an area of (60 thousand hectares) only (Bamatraf et al. 1996).

Another study confirms that the total amount of precipitation for the whole Arab world is about (223 billion m 3 / year), of which (214 billion / m3) falling on the territory of the Arabian Peninsula, an increase of (9.6 %) of the total precipitation which located the most in the Red Sea mountain range and Gulf of Aden and part of the Arabian Gulf and Gulf of Oman.

Groundwater in the land of Yemen and the extent of exploitation:

Estimated amount of groundwater Penetrating the earth's layers in the opinion of some researchers to be equivalent to a layer of water covering the globe with depth ranging between (200–600 feet).

It can get a good cover of groundwater in Yemen, where there is fractal edge of volcanic rashes configurations based on the base of the sedimentary rocks, although there are some complications due to a volcanic vertical dam Dykes) divided layers into sections, some may be dry and some other neighboring water-rich.

Groundwater in Yemen is considered the basic inventory of water resources, geological conditions represented in the nature of the rocks and the degree of cavitation and structural evolution as well as the terrain and the distribution of vegetation in different regions has helped to Surface water leak And rainwater to underground to form aquifers when rain Decreases and rivers lack, And thus the groundwater is the third source of fresh water, especially in the lowlands which are spread inside the desert areas where the low Earth's surface inside the hills allows the emergence of springs or digging wells.

Wells has increased in recent years across most of Yemen as a result of increased human use of water resulting in lower groundwater levels, especially in Sana'a province, which has seen the biggest expansion to dig wells and use the water.

In the twenties of the twentieth century was the depth of the wells, particularly in the Sana'a basin does not exceed (20 m) as the German geographic explained (Wiss Mann).

In 1973, the depth in the Sana'a Basin became (30–40m) and has reached (70 m) at the present time thus the average decline in the level of groundwater annually in the bottom of Sana'a estimated as (1–6m) and at the bottom of Imran (1–4m) a year as the studies suggest.

(the study of the southern highlands / Bamatraf et al. 1970) has indicated that the water withdrawal rates exceed Feeding Rates in most major basins areas, except for the south coast where the rates are still close to the feeding rates.

Alasttrav rates Shows (withdrawals greater than the feed rate) large in the highlands basins where reaches double, and the storage capacity of basin highlands is considered lowest among the other regions while al Mukalla extension basin (Almspl) the largest of which as much as about 10-times.

Geological formations and groundwater stocks

Which can be summarized as follows:

1. Alarceah base rocks: exist in (North-South and North-east Yemen / northern al Jawf / East West Saada / West Shabwa / Abyan / Albaedaa / west of Mukalla / Sanaa / Southeast Taiz). It is rocks do not contain water,and groundwater can develop in the cracked areas and on a small scale.
2. sandstone rocks (220 m): It is rocks with groundwater productive stocks and with medium connect.
3. Omran Group rocks (2800 m): found in areas (Imran / South laa Valley / Bagel / Al Jawf / Marib / saker / Shabwa / Saada / Alaahjr vally / mount salb / sabatain / Shakra vally tahm),, where the rocks stocks have weak productivity and weak to moderate connection while sandstone can be of productive stocks.
4. Altawele group sandstone (330 m):found in Kawkaban / Shibam / THALA / Aakecn / Frtk / Mukalla / Sherwin / Hrchian / Alhajria), which is sandstone stocks of medium productivity and medium connection. Except Alhajaria be unproductive underground stock and perhaps small productivity.
5. Alhen triple volcano rocks (600 m): are found in (south of western slopes and Central heights) and it is wide stocks (medium-to-high initial permeability) in the volcanic rock layers and (medium-high secondary permeability) in the fault zones.
6. Alsaif evaporitic rocks (100–200m): are found in (Alsaif / Mount Thma / Ibn Abbas, It is does not contain groundwater stock but is a potential source of water salinity.

Groundwater basins

First — small water basins:

Spread all over Yemen, especially the southwestern slopes of the country, where the amount of water is not sufficient, but it is important in drinking and it's location near cities and large population centers such as Shol basin (north-west of Abb) and Hawban basin (north of Taiz), and Alarhadh basin (Kersh) and Khawlan low Basins / Radaa / Anas (East Saada). The depth of the water falls from a few meters to tens of meters. Subjected to severe Luxury due to severe expansion of artesian wells for the purpose of agricultural and urban expansion. These basins are formed from volcanic layers or networking system for main rock base.

Main basins and regions of its presence can be discriminated as follows:

1. Red Sea Basin: exist in the plains and western slopes.
2. Aden Bay basin: exist in the plains with the southern slopes and Southern Western.
3. Arabian Sea basins: It stretches from the edges of the eastern, western and southern slopes to Almcilh- Hadramout valley and Alvedh basin in almehra.
4. Al Rub al-Khali basin: located in the slopes and areas adjacent to the desert in the eastern and northern regions,, and all the basins above consist of basins and valleys separated from each other vertically and horizontally, and also pour into separate zones with the exception of the Red Sea basin, all of valleys pour in the Tihama plain or Central eastern slopes, to pour toward Ramlet Alsabatain, that connect with Hadhramaut valley outwardly, while surface and underground water communication has not been proven yet, which requires that Valley Hadramout constitute an independent unit as Almhra Governorate and many other valleys.

Second-large water basins:

– Yemen is the richest source of groundwater.

– Include at least 90 % of underground water.

– The basins area reaches tens of thousands of square kilometers.

It is of two types:

1. sand rocks and Aljeria layers: located at different depths from the surface and thickness ranges from less than 100 m — 1000 m,and with slight to well water cover located in Sana'a / Saada / eastern regions still some untapped (Almaseelah basin for example)and are not affected by drought seasons, where water is considered stored for thousands of years, and most offered indirectly.
2. deltaic sediments: of great dimensions and the water cover is good to excellent, and affect slightly by drought seasons exposed to drain which exposing them to intervene with the sea water and fed indirectly of these basins:

Central lowlands Territory basins:

1. Sana'a Basin: from Dhari basins and shallowness of middle or modern life and is considered one of the most important sedimentation basins in the central highlands (2000 m above sea level), is located between the longitudes (44.10 to 44.37) east and latitudes (15.10 to 15.38) north and it covers an area of ​​approximately (1200 km 2), and the oldest rocks in the basin, is the long-formation sandstone (Alkritas), and Tkhoin Majzar rocks (Paleocene), which are located in the south-west of the basin around the city of Sanaa, and the Gharasi north east of Sanaa. There are several types of sedimentary rock firearms overlapping between the layers of basalt and crumbs fiery constituent volcainos Yemen, a Tkirna Alhadame basin surrounded by mountains, on the side of a steep hillside that leads to the flow of rain water through the water network quickly, which in turn collects in the High-layered container of water.

One of the main reservoirs in the Sana'a basin are takwene altawela layers (Alkritas), which range in thickness between 80–400m and beneath it is the composition and Valley Aloahjr (Imran Kells Group) less permeability, which in turn helps to save groundwater from leaking to the bottom, and exist of Brkanyat Yemen rocks or Brkanyat Yemen quartet splinter above the longitudinal rocks, helps on the speed of rainwater absorption.

While in places where sandstone expose directly for rain water, this water absorbs quickly, due to its breaks and cracks.

Quartet Rock opened above the basalt triple rock and Qavan basin occupies (300 m) and it is of a low permeability, the depth of underground water within these formations ranges medium between (10–30m) and water generally safe to drink, in some places with apparent salinity because of the old marine sediments. The size of the quartet formations containing water is estimated around (17.5 km 3), and for sandstone, the size of layer containing on water reaches between (300–500 km 3),

Currently depending on (45 productive wells) only, is pumped daily to the capital Sanaa of them (21 wells) in the North West field and (9 wells) in the northeastern field and (15 wells) is pumped directly into the water network of Nakem and Aser territory and Obeid and Al Rawda well.

The daily water productivity at around (53,700 m3) and the number of beneficiaries of the total project is currently (61 thousand subscribers), representing 55 % of the capital's population of totaly (141,298 people), according to statistics in 1990, the average production in 1985, equal to (25,500 m3) and there is severe drop in groundwater levels in recent years in the eastern and western wells field, which is due to depletion of underground storage of stone sandstone — Altawela,and project (Sawas) is the one who has studied several options in 1986, it aims to Specify new and additional sources to provide Sanaa with sufficient quantities of water drinking until the year 2010, it has been specified about twelve options for new sources of water during the first phase.

Dhahban Basin is the only source to extend the secretariat of the capital with drinking water, which is exposed to environmental pollution due to leak of sewage and factory water and their chemical waste into the basin, and the Yemeni government has established sewage treatment plant in Aljraf and Al Rawda areas and the outskirts of Sanaa).

the Sana'a basin data shows that total household uses the year 1990 was (22.75 million / m3), while the Ilvat consumption (59 million / m3) and Alanab (40 million / m3) and Albrsem (112 million / m3).

As a result of the unjust exhaustion and low water levels in the water basins will result in increased costs for water and depletion of groundwater resources of water. The figures also showes that the Sana'a basin in a threatening major disaster because attributed declining at a rate of (18:00 / year), and is expected to dry out in 2008 or 2010 at best estimates, Unless urgent scientific means is taken to ensure the reduction of the proportion of depletion and raise the rainwater fed rates.

2. Imran — Rida Basin: From the Alhaiat Dhari basins Central and modern located in the northeast of Sanaa between Shibam and Kawkaban south and Veban north with long more than (70 km), and is characterized to be relatively broad in the southern and central parts and narrows toward the north, and covers an area of (1280 km2) where it's territory consisting of volcanic rock and sand rises from the sea-level (2100- 2300 m), surrounded by hills and slopes reef that rises about (700 m) from the bottom of the valley and punctuated by some of the side valleys that combine with the main basin. Tt is part of gathering water basin to the valley Alkhard (major tributary of the Wadi Al-Jouf), which is located to the northeast of the Valley of Imran.

Amran basin is from unsettle basins and formed in a formative way, and bounded from the west Najd high from limestone (Imran group) and from the east limestone rocks covered with sand rocks (altawela configurable) and basaltic mattresses, abound on sides broken rims with big tendencies, especially on the west side of it.

And the groundwater depth ranges between (25- 55 m) in the center of the basin and between (10–70m) on the edge of the basin, and its depth in Quartet torrents of Saliyah and limestone usually ranging between (10–20m).

And Imran group limestone rocks, Altawela sandstone, would represent groundwater basis in this basin,, and the rocks of some springs of fresh and alkaline water appear in some fissures and cracks places in the limestone containing karstic lowland in Amran group as in Alkhard area.

3. Saada Basin: Located in the far north of Yemen between the Algiraniah plateau east and basal mountain overlooking the Tehama west, and is located within the numerous underground water basins, the largest of which is located at the city of Saada.. The natural extension of the Jawf Valley Rift when meeting in the North with downside scope extending from north to south, and is one of the largest Alkhosfih basins (tectonic) and most contain water and reaches to about (385 km 3), and we see in Saada region many of the underground water basins with unsettle conditions. Saada basin consists of layers of Wahed sandstone above the basement complex rocks and above are Alhen Alrubaee sediments formed by alluvial deposits and surface sand, and changing of Wajed sand rocks the first place the basic ground water potable in most places, due to spreding capacity in Saada basin and it's thickness (950 m) In addition to Solid basement rocks un leaked Underneath,and that keeps groundwater from leaking to the bottom, and Saada basin extends from south to north around (25 km) and a width (15 km).

water containing layers on the change by it's categories richness of rock, gravel and sand coarse, medium and aquifers for water clastic rocks rich with soft sand and clay material and the few permeability.

Varies underground water depth of between (10–40–50 m), the basin is exposed to the process of severe depletion of water, and water mostly is good for drinking and irrigation,, but it is not free of salt water, in the true sense as the power of the electrical conductivity up between 2350–5000 Mlimosz / cm, a few proliferation. And the basin exposed to severe depletion, and which may be alarming to Saada's population, like that of many other provinces, such as Sanaa / Taiz and others.

4. Dhamar Mabar Basin: located among the highlands overlooking the town of Yarim, south and highlands that separate this lowland and Sana'a lowland.Basin consists of mainly lowland (Dhamar / Mabar) and small constructions lowlands are usually located to the main low-west are parts (Bugel / Alhakl / century Dhamar / Shraa.. etc.). The average heights ranging between (2300–2500m), there is an ancient lake occupied parts of them, especially in Dhamar — Maeer lowland, leaving behind a rich salt deposits.

We see in these basins rocks of different ages some dating back to the time of righteousness as Alameri to the Jurassic and Cretaceous then triple and quadruple, the basal rocks occupy a few places in the basin, which consists of gneiss and schist and other rocks. And the triple volcanic rocks occupies main center in the middle of rocks containing water because of the nature of these rich rock with cracks and mud Palandsasat and clay sand with thickness over than (1000 m) and sometimes up to (6000 m), the quartet volcanic sandy rocks covers good areas in the eastern sections of the basin and quartet rock formations, lowlands occupies the It is composed of water from the sandy materials and exclusive conditions and stones and mud and clay, it reaches a thickness in major basins to (600–700m), while declining in other places to less than (200 m).

Basal, limestone,stone and sand rocks It is not of great importance waterway because of the depth, as it is located at depths ranging between (300–400m) up to (800 meters) in some places, making access to water and extraction is intensive and uneconomic.

Triple volcanic rocks Considered due to the speed of spread and thickness of the rock formation containing water well so we find here is rich in water wells fed by waters of these rocks sometimes encounter heavy water fountains and most fractal or division. The water container class is rich with sand, gravel and stones, alternating with the least permeable rocks rich of fine sand and clay materials and represents rock-mentioned reaches a thickness (100 m) and more and the depth of groundwater between (4–5m) near the village of Rsabh (600 m) in the bottom of Jhran and the average groundwater (25–45m), and we find here wells rich in water, and the wells depth vary, for example, near the village of Rsabh between (4–5m), while North of the Jhran bottom between (50–60m), the water extraction is economical, It is suitable for drinking and irrigation, except for a few places where the salinity rises because of a rock-containing salts which are limestone rocks dating back to the end of the third and beginning of the fourth time which is rich in carbonate (bottom Jhran and Sana'a Basin).

Western slopes basins (swamp western slopes)

Tihama plain Basin:

A deposition Basin of Dhari basins and flats centrist and modern and be refractive / Plains feet mountains (Alipidment) flooded fans the discontinuous valleys (crescent sandy Dunes / beach / salt marshes / hanging beaches sandy beaches).

A tectonic basin restricted on the eastern side two main cracks represents the upper side of them Red Sea plateaus and Central highlands. This basin extends toward the north — northwest — south — southeast skewed slightly to the north direction from the direction of the Red Sea almost vertically from the direction of the Gulf of Aden.

Valleys has played a key role of the transfer of massive amounts of rock groups and from headwaters in the highlands of Yemen and the hills of the Red Sea to the basin on the long and successive geological periods since Alhen triple till now where formed thick layers of sedimentary rocks through Alehinin triple and quadruple,formative movements during periods depositional and even Alhen did not calm down,and through the study of the geological sector of this basin it is clear that there is an increase in the thickness of layers in a westerly direction As we move away from Cracking mountain edge.

Geophysical studies and tests (Alcirmih and Altnakulaih)has shown that the size of the granules of those rocks ranging from coarse to tiny and thus the degree of permeability decreases closer we get to the Red Sea coast to the west and was also found after the lenses and irregular layers and consisting of medical sediments. The thickness of the sediments Alhen graduating quadruple in some tens of meters near the eastern hills to more than (1000 m) in the direction of the West.

Groundwater are found in sedimentary rocks from ancient times and in the form of major reservoirs, which reaches a depth to (300 m), and rigorous testing for layers of water-bearing underground in Tehama showed that it consists of several independent quasi from underground water field and current The process of groundwater recharge occurs along the eastern edge of the area of Tihama plain.

Natural drainage is happening in the Red Sea or near its shores through the water flow beneath the Earth's surface as well as by evaporation along the coast (marshes) as well as by the extraction of groundwater, and in the region there are about (15 thousand pump) to raise the groundwater for the purpose of watering agricultural land and inventory of groundwater is enough to irrigate an area (15–20 thousand hectares). Underground water influenced by the sea where constitute a fresh cap layer above the water denser seawater.

And Alhrs is one of the richest regions of Yemen in groundwater because of its capacity, as well as receiving large amounts of water and through the steep valleys of the high mountains that receive good amounts of rain where every valley in this Plain is an independent underground water basin, as we mentioned earlier.

Groundwater in some valleys of the basin is suitable for agriculture and drinking as in the valley of Banna and is not suitable for agriculture and drinking as in Wadi Hassan as a result of over-exploitation of water in this valley. Studies have shown that approximately (50 million / m3) flows annually from the water basin to the Red Sea, while the annual groundwater recharge estimated (26 million / m3 / year) there is a shortfall of (24 million / m 3 / year), which cause low rates of groundwater in it.

Tihama plain basins consists of:

1. Moore Valley Basin: of a broader water networks in the Tihama Valley, and carried the surface water is unrivaled throughout the year stems tracts of the Red Sea hills near Hajjah Governorate (Algiraniah and metamorphic rocks spread) to pour in the Tihama plain.The layer sequence of this basin began from the highest with desert sediment (sand dunes) and beneath located thick layers of deposits slimy and the copter surface mixed with sand of the Alhen quadrilateral (Layered container of ground water), then the lower layers consisting of Filz volcanic sediment mixed with deposits and salt Mtbhrat Salif, which helps to save ground water from leaking down.

The annual rate for flood water and The floods flowing up to the Moore Valley about (237 million / m3) flowed mostly to the Red Sea after some lands of saline area are watered. The Moore Valley basin area is estimated at about (7500 km2) and a length (3000 km). This valley is the most valleys in length and the largest space and moving from north to south across the mountainous blocs, the abundant flowing attributed to passing through several climatic zones and the amount of rainfall in April by reach about (25 million / m3) and go down in August to (20 million / m3), It stops flowing to some extent in winter and autumn is not about (million / m3 / month).

2. Valley Zabid Basin: occupies second largest water networks of Tihama plain after Moore Valley, and another in which almost always water, area (4900 km2) The layer sequence of the basin, starts from the top down, of a wind desert materials, medical supplies materials blended with small alluvial sand materials, and beneath a thick layer of gravel and silt, and then another layer of gravel, sand and Alkoonjlomirat rocks, of Alhen quartet, which is the main reservoir of groundwater and the thickness ranges (50–150m) where underneath the Solid basement rocks layer and if we dive more A new layer show With less permeability,rich with medical items and considered water-bearing layer,, rainfall that flow from the hills of the Volcanic Red Sea near Dhamar ranging rate (500–800 mm) at the coastal plain area of ​​Zabid and feeds the basin of agricultural land exchange as a secondary source water after rain, so is the basin of the richest groundwater basins and most sweetness in the Tihama plain because the layer containing thick water and increased salinity the closer to the Red Sea. The basin area (4900 km2) and length is more than (250 km), and the depth of ground water of the basin, ranging from (8–56 m), and the underground water level changes according to topography of the region. And the amount of summer runoff in August is up to (50 million / m3), while no more than (10 million / m3) in April and that amount decrease in winter and autumn due to lack of rainfall.
3. Srdod Valley Basin: rivers draining lines of Srdod Valley can be divided into preliminary rivers and stems course toward the general trend from east to west. And secondary rivers and wide rivers, and controls it's direction the cracks with the north-western direction to the south-west.

Discharge of surface water in some pelvic regions throughout the year, the sedimentary cover of Srdod Valley consists of four sedimentary bands three of them belong to Alhen Alrubaee, and the layer sequence of the valley starts from the top of Valley sediments Unsaturated with water, and consists of fluvial deposits of clay, sand and gravel, while the lower scale belongs to the Alhen trio composed of clastic sedimentary rocks and evaporitic. The area of the basin is around (2450 km2) and length of about (240 km) and the valley pours in the Red Sea south of Zubaydiah.

The eastern slopes basin (catchment eastern slopes)

1. Jouf Valley Basin (Arab sea): It terrainous Bay separates the north and south of the east Algiraniah plateau, one of the longest absorbed basins causes watery surface coming from the eastern hills across the joists valleys such as the Valley of Mazhab / Alkhard / dam (Valley SABA) / Valley Hreib / Bayhan, which cut off the southern part of the region and is one of the largest water basin in Yemen. The hydrogen cycle and the natural plant life in basin region of Jawf depends on the volatile climate changes in the region. Eastern lowlands of Al Jawf Valley Stretches to long distances include the Empty Quarter, and so added to the Flocked eastern slopes.

And plant life in the north-eastern regions characterized by scarcity as well as water systems in the eastern slopes region (Wadi Al-Jouf and the Empty Quarter) characterized by it’s Fig tree. East plateaus stretches up to a Hadramout valley plateau punctuated by Hadhramaut valley,, and descended toward the east, gradually to merge in the central eastern regions to reach land located along the valleys that reach to it seasonal floods include valleys (khb / Aljawf / Bayhan / Marib).

The most important characteristic of the region that the rainfall is very low, ranging from (100–250 mm) and the greater part of them has less rainfall than (150 mm), which increases the importance of the lowland as a source of water underground that consists of thick layers of Quartet and triple Saliyah materials, which rotates the rocky acrid formations (small clay and sandy materials and rocks origin Calcareous and naval) and below exist mainly the limestone rocks and sandstone rocks to a lesser extent, both permeable rocks, so it is believed that there are two types of underground and surface water that sits in the rock formation permeability, and water underground, which sits in calcareous rocks, sandstone, located a few hundred meters from the surface.

Groundwater in this basin characterized of momentum artesian, for the abundance of groundwater which comes from the presence of large numbers of the valleys coming from the west and south (alkhadr and Mazaab and Saba... and others). Studies showed that the rate of reservoir feed in the basin of the Bayhan valley is equal to (32.8 million / m3 / year), lost and leaked water to the Empty Quarter worth (38 million / m3), which means that the annual deficit equal to (6 million / m3) approximately.

2. Rub al-Khali basin: a sedimentary basins located on the Arabian Shelf (Republic of Yemen), which contains from time to time on thick deposits, compared to neighboring areas and located on the Arab pier and is a long basin tends toward the northeast near the Alhda well area and even the Arabian Gulf and extends south to vast distances of the coast of Iran and Abu Dhabi, Oman,, even Yemen lands, generally regularly width long border and the width average (300 km) mentioned (Poweret. AL 1970).

And the thickness of sedimentary rocks consisting of gravel, sand dunes and boulders (Paleocene and early Eocene and median) increase as we head towards the center of the basin, especially the east of Amman due to increase the depth of the basin in front of Oman mountain range affected by severe folds.

Through the study of the sedimentary environment of the middle periods life rocks, it has been shown to be formed depositional shallow environment, starting from the center of the basin and in the direction of the north-west of it and even the continental shelf area in the south-western parts,, while the northern Eastern parts of the Basin, the sedimentation occurred in a deep depositional basins. The region is characterized by scarcity and lack of flow sinks ((Water Flow,, which form only in the seasons of rainfall, according to the satellite data, which showed that the Valley Amlh and Hroan to have intermittently flow, here the value of the internal flow and Internal inventory is considered excellent for limited irrigation.

The southern slopes basins (coastal plain basins Overlooking the Gulf of Aden and the Arabian Sea)

It consists of:

1. Hadhramaut valley basin: The basin of Hadramout valley and coastal strip until the Omani border.

Some studies have indicated the presence of underground water near the surface salty in the middle of the valley and the presence of other deeper parts contain huge amounts of fresh water. And be 30 % of the poor-quality water.

Torrents that flow into the sea in Mukalla Shahr area Estimated about (4,000,000 / m 3 / year) and up to more than (25 million / m3) if added to the floods in the other valleys in the same area, are source of underground water fed in the basin, which has unlimited possibilities, annual nutrition estimates of (275 million / m3).

2. Aden Gulf basin: This region receives the largest amount of rainfall in the Republic of Yemen, where a high incidence of seasonal surface, where abundant of seasonal surface water, and the most important valleys of that region (Banna valley / Tbn), who originate from the southern highlands and pour into the coastal plain of the Gulf of Aden (which stretches from the Strait of Bab Mandeb and even Oman borders) where agricultural lands irrigated by surface and underground water. The Banna Valley of the articular valleys while the Tuban Valley of the intermittent valleys, and according to the annual precipitation rain rates, water networks forms in that region of the arboreal kind.

Water reservoirs for the Southern Area

Aden is one of the most important areas in the south of Yemen, which was not devoid of wells, where in approximately (14 wells) in old times,has now raised to 180 wells but did not meet the needs of the population and some of which are closed due to high salinity at present Aden suffer landmarks crisis Supply fresh water despite Providing water from some sources (water desalination plant card 14 thousand tons / day). The tanks in Aden is one of the of water storage means, where the tanks are not filled with rainwater directly into a few rain area where in a few come down in a very spaced seasons, knowing that the tanks can be provided in the -scarce or rich water area, and people in Aden Build it in any site and for any reason requires water storage.

Table below shows the tanks and their location and their storage Capacity

number	Length (M)	Width (M)	Depth (M)	Capacity (Gallon)	Notes
1	150	60	40	1500000	At the head of a Altawela valley
2	33	20	28	54325	West valley next to (1) and connected to it through the channel
3	30	34	21	29875	West Valley and connected to the number (2)
4	45	46	27	188693	West Valley and connected to the number (3)
5	74	30	20	93000	East of the valley next to the No. (1)
6	41	26	25	5800	East valley beside the No. (5)
7	75	30	23	95987	East valley beside the No. (6) and connected to it
5+8	26	16	9	22484	West Valley tanker to prevent the fall of a small stones to No. (8) connected via a channel to the No. (4) and another across the valley to the No. (7)
8	70	70	26	508940	West Valley connected number (2/8) west valley
9	39	29	14	52500	West Valley
10	43	29	17	75181	West Valley connected number (9)
11	99	59	28	328000	West Valley and outside it
12	33	18	15	45000	East Valley and outside the cemetery overlooking the Persians
13	74	70	33	486750	a separate tank Mansouri Mountains Housh Church (tank rare)

The importance of wells and their relationship with water:

The number of operating rigs currently drilling wells to 200 rig and the number of wells have been drilled more than (45 thousand well), uses more than 85 % of them for irrigation and despite the large number of wells, but they are not subject to the legislation or controls the distribution of these wells or are determine the upper limit of the amounts used from each well or basin and the significance of this is that the number of wells in Sana'a basin unit up to the limits (15 thousand wells) in the area does not exceed (3,200 km 2) has led to a drop in water levels that reached sometimes to more (7 years) and the Yemeni water resources explained Authority that the total use of 1990 amounted to (2899 million / m3) distributed mainly as follows: (2700 million / m3) for agriculture, and (168 million / m3) for domestic use, and (3 million / m 3) for other purposes.

This means that the gap between the uses and resources of (400 million / m3 / year) in 1990 and increased to (700 million / m3) in 1995, according to the requirement of 2010 estimates it is clear that the required amounts in that year would reach (3521 million / m3).

The Yemeni Water Resources Authority explained ((in the case of low water level of one-meter means depletion of underground water reserves needed many years to recharge)) and that the low level of more than (100 m) in 20 years means the depletion of aquifers, which has accumulated over more than 400 years the problem is compounded when it is clear that more than 90 % of the volume of consumption in 1990 was used for agriculture, and a large portion of this amount (2700 million / m 3) was used either due to the low efficiency of irrigation or have been used in agricultural products without any real value to the community and for the growing need for water demand coverage in major cities is to drill additional wells work up to (100 m or 500 m).

Sources of groundwater recharge

And are implemented according to the following areas:

1. coastal plains and eastern regions: is made from surface run-off water in the valleys descending from the neighboring mountainous areas, it has found that 5 percent of the water flowing go to the Red Sea, and around (20.15 %) go to the Gulf of Aden
2. mountainous areas and central highlands: The primary source of nutrition for surface water flowing because it has the highest proportion of precipitation, but steep and the impermeable nature of the rock prevent excess water to leak into the ground in those areas, so the water is moving through the ducts plains and valleys in the regions mountain neighboring, and replenishes underground reservoirs in low-lying areas.
3. High Plains: Studies have shown that the direct feeding through rainwater leak in the high plains are less important than feeding by surface run-off water through a valleys network. Some studies also showed that the annual average of groundwater recharge in some parts of the High Plains is less than actual annual rate of groundwater extraction.

Conclusions and recommendations and processors

In light of the urban development of the population and increasing numbers over the years, it is necessary to work to insure the food security of the population, where remains the need to create a good land and expansion of the agricultural landscape. The remaining problem of availability of water for agriculture is the main problem facing the country, especially since the climate of the Republic of Yemen is hot and dry, and the annual rate of latent evaporation exceeds the average annual rainfall falling,and the government has struggled to overcome the harshness of the climatic conditions and the reduction of desertification through the creation of dams to feed the underground water reserves and the fact that the natural properties and reduce wastage, which flows into the sea and the desert, and the reduction of soil erosion as well.

Although groundwater is still the main source of water resources and the basis for agricultural development and the basis of any agricultural policy planning for agricultural future, and in order to overcome the shortage of water resources, particularly groundwater most important processors and solutions should be doing which are as follows:

1. Increase the efficiency of irrigation by (70–75 %) through land settlement.
2. Reduce the cultivation of crops that consume large amounts of water such as (Qat).
3. The use of modern irrigation systems as sprinkler and drip, according to the nature of the soil.
4. crops tolerant to drought or salt water or crops devise short-lived and high production by introducing genetic engineering within the agricultural colleges and institutes curricula to see the development of those crops.
5. Use of sea water as a source of irrigation, where studies have shown that the use of fertilizer residues poultry farms at a rate of (2 %) lead to overcoming the problem of salinity of 30 % of the sea water in the case of the use of sand and limestone land. Or the use of amino acid concentration (5 %) and in the common combination and then sprayed on the plant in a very sensitive stage of salinity (the seedlings) gave the plant a high ability to withstand high concentrations of salinity of the sea water.
6. dams and reservoirs built on the permanent runoff or recharge the water-rock canyons (rocks tanks)as an alternative to dams.
7. Reduce the proportion of evaporation from the surfaces of reservoirs and waterways by altering the course of the valleys, or the establishment of a series of low dams.
8. withdraw surplus water from countries where does not exist water projects allow the storage of its surplus.
9. use of wastewater (Health / Agricultural / Industrial) and the quantities of sewage does not exceed (37 million / m3) and taken advantage of about (20 million / m3) as a partial treatment in limited agricultural uses.
10. desalination in various ways (in Yemen are getting a small amount of seawater at the electro-thermal station in Aden only).
11. conclusion of agreements and contracts for water with abundant water resources of Arab States.
12. building Yemeni water strategy buying and selling water rights and prevent the creation of new farms and the introduction of additional taxes in the agricultural, cutting water per day for limited periods, and follow modern methods in the drilling of wells, roads, irrigation, which is the water loss very few.

References:

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