Introduction
Many researchers examined general groundwater potentialities in Siwa Oasis without going into the details of geographic distribution of these potentials including water quality.
Upon taking charge of groundwater management in the deserts, the Ministry of Public Works and Water Resources started an explanatory tour on 25 April 1996. All the ministry's leaderships in different specializations headed by the Minister and a number of specialists in other disciplines related to comprehensive development participated in that tour. A meeting with public and executive leaderships was held in the oasis to discuss their problems and get acquainted with history of development in the Oasis.
Following this exploratory tour, every sector in the Ministry presented work schemes for advancing the oasis and ensuring its sustainable development. After formulating the plan, the Groundwater Research Institute conducted a comprehensive survey of the wells and springs with the purpose of prioritization of executive works, preparing and delegating the contracting works.
This preliminary or interim report was prepared with the goal of facilitation for citizens and investors who started development in the oasis so that development works are not delayed and continuous development is not affected knowing that some field experiments are still under construction.
1- Location and Natural Conditions
1-1 Background about the Oasis conditions
Siwa Oasis lies northwest of Western Desert in a topographic depression surrounded by limestone mountains from the north and sand dunes from south. The Oasis's average ground level reaches 16m below sea level. The oasis surface is covered with sands transferred from the outputs of weathering of limestone and sand dunes ranging from 0 to 15 m followed by rifted limestone compositions formed from many zones that are separated by mud layers, followed by the regional reservoir of the Nubian sandstone containing fresh ground water.
2- Hydrogeological Context
According to excavation findings done so far, ground water basins in the oasis can be classified into two major basins, i.e. rifted limestone compositions and Nubian Sandstone compositions.
The limestone basin in the oasis is composed of two major zones. The upper zone may disappear in some areas (like Eastern Oasis) as demonstrated as follows:
a)- The upper zone of ground level extends with a depth ranging from 250 to 300m, containing ground water of moderate salinity (less than 3000 particles/million) to 250 m depth, salinity increases gradually with depth.
b)- The upper zone is followed by a lower zone with a depth ranging from 250 to 350 m, containing relatively high saline groundwater (5000-7000 particles/million).
C)- The Nubian Sandstone compositions follow at depth ranging from 900 to 1000m from ground level, containing low salinity ground water (200-400 particles/million).
The Nubian sandstone water represents the main source for charging the limestone compositions due to its high pressures, in other words water in various compositions is directly related to each other.
According to field experiments and chemical analyses, a group of hydrogeological maps were prepared demonstrating succession of layers, hydrological pressures and water quality in all the compositions, in addition to measurements of discharge rates of wells and springs and losses into drains and lakes. 3- Towards a Rational Water Management
3-1 Assessment of Current Situation
Water management aims to raise value of economic yield from water unit. Therefore the major objective on which the institute focused is controlling flowing wells' water either through rehabilitating these wells and installing control systems or closing unusable wells and replacing them with new wells on which control systems can easily be set up. Achieving that objective required gathering water users because the replaced wells usually give larger discharge than that of the original wells. Well with high losses were controlled, rehabilitated and replaced as a first phase followed by medium-flowing wells. 215 wells were closed and substituted with nearly 118 wells with controlled discharge. That coincided with measuring discharges of wells and losses into drains and ponds (19 months) where it demonstrated the following:
1- Decreasing losses to drains and ponds with nearly 40%.
2- Replanting some areas of old lands that were out of production as a result of shortage in flow of some old public wells.
3- A slight increase in flowing of springs water which led to cultivating the surrounding old lands (springs walls are elevated and provided with marwas).
A comparative Survey of Agricultural Lands is required.
3-1-2 Report concerning Follow-up of Current Works in Siwa Oasis
Background
Groundwater Research Institute made a proposal including two important parts:
1- Cessation of wasting ground water in the oasis.
2- Estimation and expansion of groundwater potentialities.
The first part includes the following:
• Controlling 68 wells in the area of Al-Maraqi Pond and dig 30 wells instead. Rate of water losses from these wells into drains network was 18.000m3 /day which represents 31% of total well discharge in the Area of Al-Maraqi Pond which are 247 wells and a spring with a total discharge of 57000 m3/day. Rise of control ratio in Al-Maraqi Area is attributed to cooperation of people with the principle of accumulation in opposition to the Siwa area.
• Controlling 30 wells in the area of Agormy Pond and digging 20 wells instead. Rate of water losses from these wells into drains network is nearly 7.620m3 /day, representing 6%of total wells discharge in the area of Agormy Pond which amounts to 526 wells and a spring with a total discharge of 120.000 m3 /day.
3- The Institute's officials measure discharges of drains into which the water of the wells that were fixed used to flow with the aim of evaluating results of rehabilitation and control.
4- As regards Siwa Pond, it is noted that there is a shortage in water losses reaching 50% despite controlling only 30% of the overall discharge of the wells pouring into that pond. As for Al-Maraqy Pond, fluctuation of discharge rates are observed due to increase of discharge of natural springs as a result of digging a well. Such a problem was set right by changing the well's design.
*Work concerning rehabilitation wells in the area of Al-Zaytoun Pond has not been finished yet, even though there are only 20 wells at most.
*It is well-known that the source of water existent at Al-Zaytoun Pond is the springs of Abou Shrouf and Qresht whose charges reach nearly 650 m3/hour. They represent a large portion of it in addition to the wells that were decided to be combined and replaced with other wells by the Groundwater Institute.
2-2 Assessment Works
1) Implementation of 12 monitoring wells of depths reaching 1200 m penetrating compositions of the Nubian sandstone. Three more others are under development distributed on the oasis to connect the sites and determine depths of compositions containing water.
2) Implementation of (1) monitoring well of a depth of 450 m permeating the layers of limestone to study hydraulic connection between zones of this composition.
3) Implementation of a productive testing well to assess the hydraulic treatments and water supply (mainly drinking water) in the areas requiring drinking water supply in consultation with the local authorities.
4) 8 testing productive wells are dug with a depth of 250 m in the areas complaining from the lack of water flow and high salinity to verify groundwater potentials. It was clear that these areas of low pressures require suction due to high salinity of groundwater.
5) A mathematical model was prepared to evaluate expansion potentialities.
3-2 Determinants of Continuous Development
Observations, experiments and measurements concomitant to groundwater works, i.e. replacement, suction experiments, excavation of monitoring wells, showed the following:
a)- Variance of groundwater potentialities in the oasis, the oasis can be distributed into two sections; east and west.
b)- Implementing a deep well penetrating composition of the Nubian sand stone leads to cessation of flow into shallow wells and springs in its scope.
c)- Upon use of pumps for abstracting groundwater in areas of non-flow, groundwater salinity increases due to bringing water from the depths (lower zone) containing saline water.
Moreover, there is the possibility of saline water creeping from the north to the oasis upon upsetting the hydraulic balance.
3-3 Development Objectives
Development aims at the following:
1 - Increase of the agricultural area and the accompanying increment in social and agricultural increase.
2 - Increase in opportunities of water bottling industry and the high economic yield involved.
3 - Growth of tourism development opportunities due to the areas of high potentialities represented in the saline lakes, the great sea sand and historical temples in addition to therapeutic tourism.
4 - International connection between Egypt and Libya .
Therefore, water potentialities had to be assessed and groundwater behavior predicted for any developmental strategy before initiating any expansion.
4- A Preliminary Report of Groundwater Potentialities
4-1 The Mathematical Model
After preparing hydrogeological maps and using estimations of hydraulic treatments, a mathematical model could be used to represent ground water motion in multi layers with the goal of simulating the current state (calibration) and predict the effect of expansion scenarios.
4-2 Simulation of the Current Situation
1- All the currently existent water sites in the oasis were introduced with their location and discharge (flow rate) where total discharge reaches nearly 500000 cubic meters per day.
2- Hydraulic treatments for all the compositions were separately introduced.
4-3 Effect of Continuation of the Current Developmental Pattern without Further Expansion
1- It is noteworthy that the flow rate does not match the cultivated area reaching 12000 feddans, rather that area may be doubled without excavating additional wells if proper water management and control systems were followed.
2- Continuing the current flow rate (or suction rate in the future), it is expected that flow of the shallow wells permeating composition of the limestone will end in 18 years.
3- It is also expected that the maximal decline in surface pressures amounts to 3.25 m.
4- Deep wells penetrating composition of the Nubian sand stone are not affected for their maximal decline does not exceed 15 years within 100 years (Note that the current pressures are 100m above ground level).
It is clear that the wells permeating composition of the limestone will end their flow after 18 years without excavating new wells rather by replicating the currently cultivated area. That change in groundwater pressures was confirmed during the last ten years (through asking the local inhabitants and published reports).
4-4 Effect of Excavating New Wells
1- Due to low density of wells and land potentials in the eastern side of the oasis, expansion was implanted in this side.
2- Owing to low groundwater potentialities in composition of limestone in part of east the oasis (disappearance of the upper zone), any expansion will depend on groundwater in the composition of the Nubian sand stone.
3- Two expansion scenarios in part of the eastern side were presented; the first involves addition of 1500000 cubic meters per day, and the second relates to addition of 280000 cubic meters per day, which shows the following:
• Any addition in the east will have a direct effect on the shallow and deep wells existent in the oasis because the main direction of water stream is southeast-northwest.
• It is expected that excavating deep wells in the east will lead to cessation of flow of the shallow wells (concentrated in the west) in three years only. It is predicted that the decline will reach 10-12 m after 100 years for the two scenarios respectively.
4- Considering that the future development will not be achieved in one phase, the projected deterioration will not occur in one time, rather on many stages.
5- The state of substituting the currently existent shallow wells (most of which in the west) with deep wells taking in consideration horizontal expansion was tested. The result showed the following expectations:
• It is expected that the maximal decline in main suction center reaches 80m in a period of time not more than 150 days. Effect of suction in the west decreases due to low water requirements in that side.
• It is predicted that deep ground water flow will end in a time period not exceeding thirty days particularly in the middle and eastern areas.
5- Recommendations
It is clear that:
1- The currently available water which is nearly 500000 m3 /day is sufficient for cultivating double the currently cultivated area, but this requires control of discharge and rationalizing water use and recycling drainage water as much as possible.
2- Any deep well penetrating composition of the Nubian sand stone will negatively affect flow of the shallow wells penetrating composition of the limestone, the only source is the Nubian sand stone.
* Excavating deep wells especially in the western and middle areas is not recommended.
3- The upper zone of the limestone composition of medium potentialities disappears in the eastern area in the oasis, so any expansion will mainly depend on deep wells, yet with making appropriate planning, design and discharge of field well.
4- Groundwater potentialities in the oasis reach 500000 m 3 per day of which 300000 in the west and 200000 in the east.
* It is recommended that the wells specifications are as follows:
| Area |
Wells Type |
Depth
(m) |
Suction
(m 3 /day) |
Area between wells (m) |
Observations |
| West |
shallow |
150 |
1000 |
500 |
Installing valves for the flowing wells |
East
(Investmentareas) |
,, |
150 |
1000 |
500 |
,, |
| East ( between Al-Zaytoun Pond and Al-Maaser Pond) |
Deep |
1000 |
10000 |
2000 |
,, |
* The need to monitor the effect of suction from the eastern area on the pressures in the investments area and the western area for formulating a policy for replacement of the shallow wells is recommended.
* The need to monitor the change in groundwater quality in the oasis and its northern part for stopping any quality deterioration before being aggravated.
6- Obstacles
• At the beginning of the project, a number of local inhabitants started digging wells in scattered places, but the Ministry sent a letter for the governor to prevent any new works. The irrigation engineer will continuously block the wells that were dug.
• Absence of cooperation of some local inhabitants in rehabilitation and accumulation operations.
• Existence of some wells of the North Coast Construction Authority that are to be operating for various purposes by the Authority.
• Flow of investment applications for different purposes which requires accuracy in assessment and deliberation in issuing approvals till confirmation of the source.
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