Abd-El Monsef, Hesham

Aufmuth, Joe

Smith, Scot E.

English

Woods Hole Open Access Server

  107GEOLOGICAL SETTING AS AN IMPORTANT FACTOR IN MANGROVE PLANTATION SITE SELECTION IN THE RED SEA  Hesham Abd-El Monsef  Joe Aufmuth  Scot E. Smith  Abstract:  Mangroves play a vital role supporting the surrounding environment. Mangrove thickets are the natural nursing grounds for hundreds of aquatic species, including economically important fish and shellfish. Mangroves play an important role in controlling erosion and protecting the coastline. Along the Red Sea coast in Egypt, mangrove stands are distributed. Since the mid- 1980s, these stands have been threatened by rapid tourist development and grazing by Bedouins. The size and the number of these stands have been reduced and many of the stands have been destroyed completely.  Thus, it is necessary to conserve the existing mangroves stands and plant mangroves where ever they can be grown. This paper describes a method to locate the best suitable sites for mangrove plantations along the south Egyptian Red Sea coast based on the geological setting of the area. Geological characteristics such as soil types and soil renovation resources, geomorphology, discharge of drainage effluents will be considered as primary sitting criteria. Different types of satellite images and data elevation models (DEM) will be interpreted to determine some of the parameters. A field check will be carried out as necessary.  Keywords: mangrove, geology, remote sensing, GIS, plantation, conservation, environment  Introduction Mangroves protect shorelines from erosion by stabilizing sediments with their tangled root systems. They maintain water quality and clarity, filtering pollutants and trapping sediments originating from land.  Mangroves function as nurseries for shrimp and recreational fisheries, exporters of organic matter to adjacent coastal food chains, and enormous sources of valuable nutrients.    108 Fig. (1): Location of some Mangrove stands along Red Sea, Egypt.    109Small mangrove stands are distributed along the Red Sea coast in Egypt (Fig.1) These stands have been rapidly destroyed in recent years due to the rapid development tourist activities and old running problem of over grazing and using the trees as fuel.  Although ministry of environment’s Red sea rangers are implementing a successful Mangrove conservation management plan but the existing Mangrove stands sites are few and need to be increased by through Mangrove plantation.  It is difficult to generalize the parameters determine sites of successful mangrove plantation but the most common parameters may include: water salinity, water temperature, tidal and wave energy, soil type and soil stability and flooding regime, spacing and thinning of mangroves, weed eradication, nursery techniques, community participation and total cost of restoration measures.  Temperature and salinity seem to be the same along the entire study area (Fig. 2) on the other hands spacing and thinning of mangroves, weed eradication and nursery techniques are parameters related to the plantation techniques more than site selection.                                                                                                                       Kelvin Fig. (2): Water temperature in along the study area.  (Reading e-Science Centre (ReSC) is hosted at the NERC Environmental Systems Science Centre (ESSC):  http://lovejoy.nerc-essc.ac.uk:8080/ncWMS/godiva2.html# )   110 Geological characteristics such as soil types, stability and soil renovation resources, surface geomorphology including slope, aspect, protection from direct high energy waves, and safety from flash flood will be considered as primary criteria for selecting sites suitable for mangrove plantation Surface Geomorphology:  7.5-Minute Data Elevation Model (DEM) with 30- x 30-meter data spacing had been used to construct a 3D model of the study area (Fig. 3). Also, DEM was processed by the ArcGIS spatial analyst extension to determine the surface slope (Fig. 3).   Fig. (3.a): Data Elevation Model of the Northern Sector.   111  Fig. (3.b): Data Elevation Model of the Southern Sector.   Fig. (4-a): Slope of the northern sector.   112 Fig. (4-b): Slope of the southern sector.   It is important that mangrove plantings be carried out on low energy areas where coastal erosion is minimal (Kairo, 1995). A the three dimension (3 D) model constructed by dropping the panchromatic TM image over the DEM, then used with slope grid of the study area to locate sites protected from direct sea waves and with low to moderate slope. Seven locations found to meet these criteria (Fig. 5).    113  Fig. (5): Three dimension (3D) module for the study area shows seven primary selected locations for mangrove plantation.   The selected sites located on or near the outlet of the drainage basins drained from West to East. The history of the study area shows a very arid climate with years of dry seasons and sudden flash flooding, so special attention must be paid to soil stability and the flash flood potentiality of the study area drainage basins.    Basins Flash Flood Potentiality:  River Tools Software version 3.5 had been used to define the drainage network of the study area using the Data Elevation Model (DEM). An enhanced Panchromatic Thematic Mapper (Fig. 6) had been used to check and corrected the resulted drainage networks. The basin boundaries were defined manually (Fig. 7).    114Fig. (6-a): Landsat TM panchromatic image of the northern sector showing the basin boundaries.  Fig. (6-b): Landsat TM panchromatic image of the northern sector showing the basin boundaries.   115 Fig. (7-a) Drainage networks of the northern sector, basin boundaries shown in black.  Fig. (7-b) Drainage networks of the southern sector, basin boundaries shown in black.   116Several drainage basin geomorphometric parameters contribute to the possibility a flash flood will occur in any particular drainage area (basin flood potentiality):  Drainage basin area, it is the most important basin characteristic for hydrologic analysis. It reflects the volume of water that can be generated from a rainfall.  Basin Length, it is the length measured along the principal flow path from the watershed outlet to the basin boundary. It is a measure of the travel time of water through the basin.  Basin slope, it affects the momentum, speed and concentration of runoff. The possibility to start a runoff is increased with the increasing of slope. The average slope of basins had been determined by dissolving the slope grid derived from DEM (Fig. 4) by basin names.  Basin Shape, shape of the basin reflects the way that runoff will stream through different parts of the basin and how the runoff dashing out the outlet. A circular watershed would result in runoff from various parts of the watershed reaching the outlet at the same time. An elliptical watershed having the outlet at one end of the major axis and having the same area as the circular watershed would cause the runoff to be spread out over time, thus producing a smaller flood peak than that of the circular watershed. Basin shape estimated by determining basin circularity ration (Fc) and basin elongation ration (Re) (Uditha, 2005):  Fc = P/(4πA)0.5 Where, P and A are the perimeter and area of the watershed, respectively.   Re = 2/Lm(A/π)0.5 Where, Lm is the maximum length of the basin parallel to the principal drainage lines.   Drainage density and stream frequency, these are the total length and total number of the entire stream segments in a drainage basin divided by the total area of the drainage basin.  High drainage density or/and stream frequency of a basin indicates a rapid storm response and consequently high probability to form flash flood (Strahler, 1981)   Bifurcation Ratio, it is defined as the ratio of the number of streams of any order to the number of streams of the next highest order. The lower bifurcation ratio indicates a circular basin with high flood potentiality and vise versa. In order to determine the bifurcation ratio the steam order - which determined the degree of stream branching within a basin - had been determined for the entire segments in each basin using Horton law (Horton, 1932) (Fig. 8).      117  Fig. (8): Stream order of Wadi Umm Gheig drainage segments.  The bifurcation ratio of a basin is the average of the bifurcation ratios of each stream order:  N = 1 Rb = [ ∑  Sn / S(n+1)] / (I – 1) N = (I – 1)  Where, I    Basin order. Sn  Number of segments of order n Rb  Bifurcation ratio  The flash flood potentiality of each basin has been evaluated based on its geomrphometeric parameters (Table 1). See Figure (9)      118Table (1-a): Geomorphometric parameters and flood potentiality of North sector basins. Basin Name D F Rb Slope Perimeter (km) Area (Sq. km) Basin Length(km) Circularity Elongation Flood Potentiality W. Sifayn 1.960 2.290 4.00 1.30 33.401 37.802 13730 1.533 0.505 High W. al-Ejlah 1.860 2.280 4.00 1.63 69.836 169.382 26360 1.514 0.557 Moderate W. Jabal El-Rasas 2.000 2.100 4.33 1.44 39.050 51.779 16720 1.531 0.486 Moderate W. Abu Eriki 1.840 2.470 3.50 1.50 48.413 76.666 17410 1.560 0.568 Moderate El-Nabaa 1.840 2.390 4.60 1.84 147.267 749.231 46550 1.518 0.664 Low W. Abu Dabbab 1.860 2.270 4.25 1.63 67.603 186.221 25480 1.398 0.604 Low North Abu Dabbab 2.110 2.120 4.00 1.39 29.062 32.652 10690 1.435 0.603 Low W. Mubbarak 1.820 2.300 4.20 1.77 154.837 830.794 52020 1.516 0.625 Low W. Umm Gerifat 1.920 2.020 5.33 1.50 58.946 87.368 23490 1.779 0.449 Moderate Ras Toronbi 1.910 2.240 4.00 1.35 49.381 102.788 17540 1.374 0.652 Low South Umm Gheig 2.040 2.170 4.00 1.05 28.555 35.851 10440 1.346 0.647 Low Umm Gheig 1.860 2.250 4.20 1.82 172.280 873.207 49130 1.645 0.679 Low South Sharm El-Qibli 1.980 2.350 3.75 1.18 45.704 95.563 16540 1.319 0.667 Moderate Sharm el-Qibli 2.030 2.240 4.00 1.64 53.919 146.862 20480 1.255 0.668 Low Sharm el-Bahari 1.930 2.330 4.50 2.27 84.722 189.076 30900 1.739 0.502 High W.  Esel 1.870 2.340 4.40 1.87 149.957 644.434 36940 1.667 0.776 Low D = Drainage Density               F = Stream Frequency                Rb = Bifurcation Ratio  Table (1-b): Geomorphometric parameters and flood potentiality of South sector basins. Basin Name D F Rb Slope Perimeter (km) Area (Sq. km) Basin Length (km) Circularity Elongation Flood Potentiality Wadi Khashir 1.68 1.97 4 1.6 146.348 94.038 24790 2.193 0.551 Moderate Wadi El-Radah 2.03 2.3 4 2.63 140.881 70.804 27190 1.683 0.493 High Wadi Hamata 1.92 2.43 4.75 1.82 260.366 85.141 29950 1.489 0.608 Low Wadi Shawab 1.84 2.34 5.25 2.58 389.764 105.724 49930 1.511 0.446 Moderate Wadi Umm El-Abas 1.99 2.46 3.6 1.74 258.640 74.838 27290 1.313 0.665 Moderate Wadi Iriar 1.88 2.32 4.75 2.22 255.668 81.957 27860 1.446 0.648 Low Wadi El Gemal 1.81 2.42 4 2.37 1952.989 300.404 54180 1.918 0.921 Moderate Wadi Ghadir 1.8 2.32 3.8 2.21 511.914 142.809 34140 1.781 0.748 Moderate Wadi an-Nakari 1.97 2.2 3 1.42 48.939 37.505 13510 1.513 0.584 Moderate Wadi Sibikhay 2 1.96 3.33 1.79 23.328 27.282 10880 1.594 0.501 High Wadi El-Anba'ut 1.85 2.39 4 2.3 98.508 53.066 21890 1.509 0.512 High Wadi Umm Tundubah 1.82 2.11 5.33 1.65 74.477 55.168 16450 1.804 0.592 Low D = Drainage Density               F = Stream Frequency                Rb = Bifurcation Ratio    119 Fig. (9-a): Flash flood potentiality of basins of northern sector.  Fig. (9-b): Flash flood potentiality of basins of southern sect   120 Soil Stability, Type and Renovation: The textural composition, salinity of the surface layer and the occurrence of anaerobic layer appeared to have played a major role in determining the establishment and growth of mangrove plants. The occurrence of aerobic surface layer and anaerobic subsurface layer supported maximum seedling establishment (N.R. BHAT AND M.K. SULEIMAN, 2004).  Previous projects for mangrove plantation in condition similar to that of the Egyptian Red Sea coastal environment showing that mangrove plantation are more successful in soil with high sand contents and low silt and clay fractions and low Caco3 content. This condition along with the fluctuating water table appears to have prevented excessive salt accumulation particularly above the tidal line. In contrast, the presence of silt and clay and water saturated anaerobic horizons in the mudflats are probably responsible for increased salinity of soils at some places (Table 2) (Kuwit project Reference, 200x).    Table (2): Key to landform, soil type and mangrove growth in Kuwait project     121The characteristic of the soil cover the Red Sea coast is affected mainly by the type of rocks exposed locally and the soil transported from the basins that drained to the Red Sea from the West.   The following is a trial to evaluate the capability of each basin on the study area to be a source of the soil suitable for mangrove plantation. The following are the parameters used:  Factors affecting the erosion and weathering process: • Lineament Intensity (Fig. 10). • Drainage density. • Mineral composition. • Area of rock exposed on the surface (Fig. 11). This layer is based on the geological map published in 1978 by the Geological survey of Egypt (Aswan Quadrangle), boundaries of the rock unites corrected and checked against Landsat thematic Mapper image. Factors affecting the transportation of soil: • Basin Order. • Basin Bifurcation ratio. • Drainage density. • Slope. Factors affecting the soil texture and soil mineral composition: • Mineral composition of the exposed rocks. • Area of rock exposed on the surface. Taking into consideration that the suitable soils for mangrove plantation are those with high sand content and low clay and calcium carbonate content, the formations and rock groups exposed on the surface on the study area has been ranked based on the mineral composition of their rocks (Table 3). For example, granitic rock will be assigned moderate rank because when weathering process affects granite the following components are released: • Oxides of iron and alumina (sesquioxides Al2O3, Fe2O3). • Various forms of silica (silicon-oxide compounds). • Stable wastes as very fine silt (mostly fine quartz) and coarser quartz (sand).  Although one of the erosion product of granite will be sand particles, but Aluminum silicates derived mainly from the Feldspar minerals (Orthoclase  and Microcline KAlSi3O8 and Albite  NaAlSi3O8) react with water to give clay minerals (colonization process). Another example is the formation composed mostly of CaCO3 rocks will be ranked down because the acidity of the sea water at the study area is low (ph is high) (Hassan and Shabara, 2003), as the water becomes less acidic, CaCO3 become insoluble and accumulated around the plant roots.     122Soil suitability factor was determined for every rock unit exposure within the basin using the following equation:  Soil Suitability Factor = (Area/Basin Area) + (Basin Order/Maximum Basin Order) + (DD/Maximum DD) + (Rb/Maximum Rb) + (Slope/Maximum Slope) + (LL/Maximum LL) + (Lithology Rank/Maximum Lithology Rank)  Where, DD = Drainage Density Rb = Bifurcation Ratio LL = Lineament Intensity Soil suitability factor was determined for each basin by averaging those of all rock unit exposed within the basin (Table 4).    Fig. (10-a): Structure lineament of the northern sector.   123 Fig. (10-b): Structure lineament of the Southern sector.  Fig. (11-a): Lithological map of the northern sector.   124   Fig. (11-b): Lithological map of the southern sector.              125  Table (3): Ranking of the Lithological composition of the formations and groups  exposed on the study area.  Lithology Rank Biotitew, Chlorite schists, metagreywacke, metamudstones, phyllite, slate and conglomerate 1 Gypsum and Samh Formation 1 Limestone with flint and Shale 1 Serpentinite and talc carbonate 1 Tarawan Chalk and lower part of Esna shale 1 Psammitic hornblende and biotite gneiss and migmatite 1 Conglomerate, brecia, graywacke, arenite and siltstone 2 Marine Deposites 2 Metagabbro and Diorite 2 Olivine gabbro, norite and tractolite 2 Slightly metamorphosed andesite, prophyrite, and pyroclastics rocks 2 Coarse brecia and fine lacustrine 3 Effusive felsite, felsite prophery, and quartz prophyry bodies 3 Granite and Granodiorite 3 Gravel, Sand and Mud 3 Rhyolite, dacite, andesite, basalt and pyroclastic rocks 3 Granodiorite 4 Sandstone with some shale 4              126 Table (4-a): Soil suitability factor for Northern sector basins.  Basin Soil Suitability Factor North Abu Dabbab 9.85 South Sharm El-Qibli 13.74 Wadi Umm Gerifat 2.17 Ras Toronbi 11.62 South Umm Gheig 5.03 El-Nabaa 99.22 Sharm el-Bahari 30.78 Sharm el-Qibli 19.22 Umm Gheig 131.62 Wadi Abu Dabbab 23.87 Wadi Abu Eriki 12.12 Wadi al-Ejlah 24.31 Wadi Esel 75.56 Wadi Jabal El-Rasas 8.23 Wadi Mubbarak 100.69 Wadi Sifayn 6.95   Table (4-b): Soil suitability factor for Southern sector basins.  Basin Soil Suitability Factor Wadi Iriar 36.54 Wadi Umm El-Abas 26.87 Wadi El-Radah 5.75 Wadi an-Nakari 12.24 Wadi El Gemal 121.68 Wadi El-Anba'ut 21.40 Wadi Ghadir 92.33 Wadi Hamata 18.11 Wadi Khashir 25.11 Wadi Shawab 20.60 Wadi Sibikhay 6.21 Wadi Umm Tundubah 27.21    127 Based on the slope, flood potentiality and soil suitability factor of those basins with an outlet drained to the pre-selected sites (Fig. 4) were categorized according to their suitability for Mangrove plantation into three categories: good, fair and poor (Table 5) (Figure 12).       Table (5): Site suitability. Name Slope Flood Potentiality Soil Suitability Site Suitability El-Nabaa 1.84 Low 99.218 Good North Abu Dabbab 1.39 Low 9.850 Poor Ras Toronbi 1.35 Low 11.618 Fair Sharm el-Bahari 2.27 High 30.777 Poor Sharm el-Qibli 1.64 Moderate 19.222 Poor South Sharm El-Qibli 1.18 Moderate 13.739 Poor South Umm Gheig 1.05 Low 5.032 Poor Umm Gheig 1.82 Low 131.619 Good Wadi Abu Dabbab 1.63 Low 23.871 Poor Wadi Abu Eriki 1.50 Moderate 12.115 Poor Wadi al-Ejlah 1.63 Moderate 24.310 Fair Wadi Esel 1.87 Low 75.563 Fair Wadi Jabal El-Rasas 1.44 Moderate 8.232 Poor Wadi Mubbarak 1.77 Moderate 100.691 Good Wadi Sifayn 1.30 High 6.951 Poor Wadi Umm Gerifat 1.50 Low 2.169 Poor    128Fig. (12): Site Suitability for Mangrove plantation.   REFERENCES:  Hassan El-Banna Awad and Sayed A. Shabara, 2003. Marine Water Quality in the Red Sea. Unpublished report.  U.S. Agency for International Development, Program Support Unit, Egyptian Environmental Policy Program, Hurghada, Egypt.  Horton, R. E. 1932. Drainage basin characteristics. Transactions of the American Geological Union, 13, 350-361.  Kairo JG. 1995.  Artificial regeneration and sustainable yield management of mangrove forests in Gazi Bay, Kenyam. M.Sc Thesis, University of Nairobi, Nairobi, Kenya, pp 116.  N.R. Bhat and M.K. Suleiman. 2004. Classification of Soils supporting Mangrove Plantation in Kuwait. Archives of Agronomy and Soil Science. 50: 535 – 551.    129Strahler, A.N., and A.H. Strahler. 1983. Modern Physical Geography. 2nd ed. New York: John Wiley & Sons.  Uditha Ratnayake. 2005. Engineering Hydrology Lecture Note. University of Peradeniya. Civil Engineering department, Sri Lanka.  

Geological setting as an important factor in mangrove plantation site selection in the Red Sea

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Geological setting as an important factor in mangrove plantation site selection in the Red Sea

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