SUDAN

6 September 2004 - 15 October 2004

Lahmeyer International

LAND USE SPECIALIST

Merowe Dam Implementation Unit

Semi-detailed Soil Survey

 

The Client The pleasure of survey in sand What it is hoped can be achieved The wet side of crossing the Nile The Consultant

Six weeks in northern Sudan in the Multaga Dongola area of Nubian Desert plus database development in the Khartoum office:

      Supervised soil survey executed by staff of the Land & Water Research Centre (LWRC) of Wad Medani for the Merowe Dam Implementation Unit (MDIUP) on contract to Lahmeyer International

      Checked field descriptions of soil profile pits in the field and checked soils descriptions produced - adding mapping codes and soil series before passing for data entry in onto computer in the field camp

      Rebuilt, collated and developed the draft database compiled in MS Excel to allow generation of physical land suitability rating or classification for the point-data (8,000+ auger observations and 140 profile pits) via look-up tables covering gravity, overhead and irrigation drip systems

      Drafted routine for use via GIS to increase ease of production of soil maps and developed routine for GIS production of Land Suitability maps for gravity, overhead and drip irrigation

      Collected, collated, checked and added all laboratory data to the database

      Finally recompiled full database in MS Access with view to incorporation into the FAO database SDBm via import routines

Other Activities:

Introduced Project and LWRC staff to the FAO multi-lingual database SDBm-plus into which soil profile data were being entered for storage and reporting purposes

 

This was a real challenge and everyone in the UK said "you are mad at your age to go and try and work in the desert".  Well they were nearly right as the temperatures did get over 50 degrees centigrade at times but old soil surveyors can keep going and can still enjoy the desert - apart from when the driver gets you stuck on a sand dune and the way out was walking 5km in the heat of the day. Anyway we made it out and, thanks to the GPS, got back to the vehicle and driver with help about 3 hours later.

All the survey sites, over 8,000 of them, were pre-selected on a grid system on 1:20,000 scale ortho-photos and GPS was used to navigate to the sites - both by the survey teams and the supervisors. There were up to 12 augers working per day so there was a lot of field and office checking to do - hence no days off at all.

The real challenge was in cleaning up the data in the database and using that data to allocate physical land suitability classification for irrigated agriculture - this was achieved and ratings were developed for all points for surface (gravity), overhead and drip irrigation systems.  Look-up tables developed in Bhutan were edited and further developed for this purpose.  The database was then incorporated into the GIS system to allow the suitability ratings (as well as soil series and soil classification codes) to be plotted directly onto the ortho-photos as an aid to final mapping.

There will be problems in developing irrigation in this area, either side of the river Nile, due to a lot of mobile sand - sand dunes - but there is a lot of irrigable land hidden away under the gravel and sand skim over much of the project area.  If the resource cannot be used now it will be there for the future when more sophisticated or robust waters distribution systems may well exist.  Normal irrigation canals would be at serious risk from being filled up, rapidly, by the mobile sands.

Amazingly well structured soils exist below a skim of sand and gravel. These soils are very hard when dry but are very friable when moistened.  Salinity and sodicity is not a major problem and inherent plus potential fertility pose no problems.  One cause for concern could be the friability of the moist soils and care could be required to avoid triggering erosion.

Wind is a major problem in the survey area - the above photo shows the features that are etched by the wind on any exposed soil profile.  Mobile aeolian sand is, however, the main problem and soil profiles can be filled within hours and there are major sand dunes which have smothered several previous irrigation schemes.

A first draft, rough idea of the distribution of land suitable for irrigation is shown opposite where the point data from the database have been dropped onto a map within the GIS.

The blue area is the actual Merowe Dam and the curving course of the Nile can be seen with:

Green areas = suitable for GRAVITY irrigation (best use)

Yellow areas = suitable for overhead / sprinkler irrigation

Purple areas = suitable for drip irrigation and

Red areas = not suitable for irrigation

This map should not be taken as any sort of authority on the final suitability of the land along the course of the Nile and is very generalised whilst the official final Project mapping will be compiled at 1:20,000 scale and include the boundaries of the soils mapping units established during the survey.  The map opposite merely serves to show that soils / land suitable for irrigation do exist in the areas surveyed.

 

 

 

 

Austin Hutcheon 1st November 2004