Identification of micro and macro watersheds through GIS and Google Earth tools andpreliminary field scooping exercise for locating/rehabilitating small earth dams within theconcerned areas:

Purpose: The aim of the exercise is the identification of existing infrastructures (small earth dams) andlocation of potentially suitable sites for the construction of new ones in order to generate a broad-spectrumenvision of the situation at the selected project area and so plan a proper intervention strategy. It wasimportant to ‘visual-map’ the project area so as to envisage the area that will be covered and pre-familiarizewith the terrain together with the presence and location of Bomas.

Although the Project Team had already a full picture and deep knowledge of the area of intervention, a firstidentification of macro and micro watersheds has given the opportunity to start making furtherconsiderations on different catchments and potentially suitable areas for the construction and rehabilitationof small earth dams. While large watersheds may be more suitable for the location of submersible dams, forsmall earth dams it is more advisable to identify small catchment basins with a limited amount ofpotentially stored water.

The field visits were performed at the beginning of August 2015. Specifically, this activity involvedcommunities’ engagement into sites assessment as a follow-up for previous introductory meetings held ineach village and pinpoint of the suitable sites. The aim was to involve the local communities to be engagedin the decision-making process since the very beginning to determine some sites where a preliminarysurvey (GPS track of the watershed border and topographic survey of the potential sites of construction)would be carried out.

Methodology:

Tools and layers to be available:- Qgis 2.x - Google Earth- Administrative boundaries layer- Water network (lines shapefile)- Digital Elevation Model (DEM). The source is the of the raster files is the U.S. Department of the

Interior- U.S. Geological Survey http://earthexplorer.usgs.gov/ or ASTER Digital Elevation Model(Ministry of Economy, Trade and Industry of Japan (METI) http://gdem.ersdac.jspacesystems.or.jp .In this case the former has been used. Starting from the DEM, the “Filled DEM” (Fill sinks-SAGA) hasbeen produced to reduce errors and avoid empty spaces with the creation of the channel network

- Slopes. The raster can be calculated through the “Terrain Analysis” “Slope”- Tablet with GPS and Locus free software, Garmin GPS or any alternative GPS device

Outputs:

- Existing and proposed location of small earth dams and amendment after the field survey (Points)- Macro-watersheds layer (Polygons)- Micro-watersheds layer (Polygons)

Initially, the identification of existing infrastructures and potential areas for the construction of small earthdams and submersible ones has been done through the use of aerial photos (Google Earth). The firstlocation of sites relied on the experience and previous surveys undertaken by the Project Team during theproposal writing phase and even beforehand. The point file create in .kml has been imported onto Qgis andsaved as shapefile.

As a very first steps, some major watersheds have been identified across the concerned area. This facilitatessome initial thoughts on the main water streams (permanent or temporary rivers, the latter namedKorongos in Swahili) and then the identification of the most appropriate sites for the construction of asubmersible dam. This can even favour the identification of areas of potential interest for small earth dams.These, and likewise the micro-watersheds afterwards, have been outlined as a polygon shapefile thanks tothe use of other layers on the background, namely:

- The water network (lines shapefile) digitalised on the basis of aerial photos and surveys on theground, output from the a previous project financed by the Italian Foreign Ministry (MAE) duringthe period 2009-2012;

- The hydrographic network created through the specific SAGA function “Channel network” (usingthe “Filled DEM” and ”Catchment area”);

- Altimetry obtained from the “Filled DEM” through the function “Extraction”“Contour” (10m asinterval between the contour lines) in the raster analysis.

The main problem encountered consisted in some discrepancies between the two layers Channel Network(calculated from the DEM) and rivers (digitalised previously). Albeit in many cases the two have resultedsimilar, in others the comparison has shown substantial differences which have been checked throughGoogle Earth to understand the actual picture. In some cases the Channel network created through the GISfunctions have been more realistic than the network already in possess (even though frequently theopposite has happened), while in other cases they have differed substantially from the situation on theground.

The identification of macro and micro watersheds in suitable areas has taken into account: i. Slopes -suitable sites should be located in areas with 0 to 5% of slope and not very steep upstream, according to theexperience and literature (FAO, 2010). Slope raster file has been created from the filled DEM andrecalculated for the target range (0-5%; 5-10%; 10-20%; more than 20%); ii) Aerial photos: to identify themost suitable morphological conditions on Google Earth according mainly to the experience of the WaterAdvisor (Mr. Giorgio Cancelliere) and previous surveys carried out by the Project Team; iii) Thecharacteristics of the hydrological network (f.i. where one or more streams/tributaries meet the mainchannel, the site may offer maximum storage).

Although the watersheds polygons can be automatically created using SAGA functions (“Channel Network” “Catchment Area” “Watershed basins” “Polygonize”), the results have been unsatisfactory andunreliable if compared to the actual situation. This may depend on the unique characteristics of the area.

The identification of micro-watersheds has been carried out in parallel with and completed after the firstfield visit undertaken by the Project Team at the beginning of August 2015. This has allowed to eventually

confirm or re-shape the watersheds according to the situation on the ground and include others. TheProject Team engaged the local communities into the process of selection of the sites potentially suitablenot only from a technical point of view but also at social and political level, giving importance to a correctgender balance and minimising the risk of conflicts. The sites have been therefore finally identifiedaccording to the local community suggestions and the participatory approach undertaken resulted in takinginto account the expectations and preferences on the sites selection. Technically, the Project Team made fullprofit of the field visit to evaluate the sedimentation patterns, probable flow speed, morphologicalcharacteristics of the sites and visual banks resistance and strength of the already existing dams. The visitalso helped the team to familiarise with basement characteristics and observe percolation/permeabilitystatus of the bed-rock should there be any intended intervention e.g. excavate submersible dam, barrage ora transversal trench. Furthermore it allowed to assess the slope previously calculated through GIS tools.

The potential sites resulting from the field survey have been digitalised in Google Earth, saved in .kml andimported and saved in Qgis as shapefile (points).

Results: 10 macro-watersheds had been identified and had been analysed afterwards to understand thereal suitability against the characteristics of the area, the administrative borders and the knowledge of theterritory by the Project Team. According to the shapes outlined in Qgis, the watershed basins’ areas varyfrom approximately 5 to 38 square Km. One of them has been retained as potentially interesting for a pre-feasibility study for the construction of a submersible dam and re-shaped after the identification of themost suitable site.

At a later stage, 10 micro-watersheds (Fig. 1) have been identified as potentially suitable for theconstruction of small earth dams against the criteria defined above. 2 of these are located in the area ofLemanda, 7 in Engutukoit, 1 in Mkuru.

Fig. 1 – Micro-watersheds

Considering also the 10 micro-basins previously designed, 7 existing and proposed dams to be potentiallyconstructed/rehabilitated have been retained through the G. Earth analysis: Mkuru dam (E, previously

realised by Istituto Oikos), Lemanda dam (P), Engutukoit dam (E, previously realised by Istituto Oikos),Engutukoit School dam (P), Engutukoit (colonial) dam (E), Taico small dam (E), Gorge Engutukoit (E).

Finally, after the field survey the potential sites identified became 5, taking into account the morphologicalcharacteristics and the preferences at local community level (Tab. 1):

Name Existing/Proposed UTM coordinatesLemanda 1 Proposed 0242335 E – 9655178 SLemanda 2 Proposed 0242706 E – 9654568 SEsilalei dam Existing 0251411 E – 9659090 SBaboon cave dams Existing 0253055 E – 9658408 SEngutukoit (colonial) dam Existing 0253633 E – 9658279 S

Tab. 1 – 5 sites selected

Taico small dam (E, private dam) was then excluded being private and potentially susceptible to localconflicts (in particular as emerged in the following surveys). Mkuru dam (E) was excluded due to a numberof already interventions made, while a suspended dam located in Engutukoit subvillage has been latelyconsidered as not of interest by the institutional representative due to distance and particularlyunfavourable environmental conditions and accessibility. Other two sites Engussero1 and Engussero2 werevisited for other kind of interventions, like reforestation and soil protection.

The results from the field visit on the 5 selected sites are (extract from the report by G. Cancelliere, August2015):

Lemanda

This is the village mostly inhabitated by agropastoralists. The intervention considered here is to excavateearth dam(s) to serve for cattle drinking and also construct a downstream cattle trough. Two sites werevisited:

The first location (Fig. 2) is at 0242335 – 9655178 point (UTM). Generally, the morphology found suitable toconstruct a barrage. During raining season a lot of water run from the upstream land and finally pours waterinto the stream.

Fig. 2 – Lemanda 1

The second location (Fig. 3) is the same old spotted site during the preliminary survey (proposal phase) andreported in the Project document. The location is at point 0242706 – 9654568 (UTM). This again is a verysuitable location for dam excavation. The next activity will be to carry out a topographic survey in order tomeasure the watershed area.

Fig. 3 – Lemanda 2

Both locations have to be surveyed and findings will be shared with the community for final selection BUTthe ultimate optional choice will depend on sufficient budget availability and estimation.

Engutukoit

This is a typical pastoralist village, annexed from Losinoni village. The project intervention plan here is toexcavate earth dam(s) to serve livestock and construct a cattle trough downside. Four different sites werevisited and evaluated accordingly:

a) Esilalei dam (Fig. 4): The first location is an existing colonial earth dam now silted with its banks partiallydemolished. The site is called Esilalei; the dam serves both people and cattle. It is located at point 0251411–9659090. This dam was severally visited by Oikos team in the past and it is a potential suitable site to catchthe runoff. The following measures are recommended for the site:-Build gabions upstream so as to reduce siltation-Rip the compacted soil so as to deepen the storage area-Rebuild the banks. -Undertake detailed topographic survey so as to locate sedimentation barriers.

Fig. 4 – Esilalei dam

b) Engutukoit (colonial) dam (Fig. 5) The second location is nearby the main korongo within the sub-villageof Engutukoit:Here an old earth dam was constructed in the stream but destroyed during El Nino (1997/1998) havoc. Thefollowing are main findings at the site:-This dam does not have a spill over-The torrential stream is a risk factor to re-consider this location. -The strong flow of the water is caused by a nearby steep slope. -The overhanging area presents an interesting catchment area to develop a storage point just before thesteep slope. -Solid transportation is limited. -Necessary to do a more detailed survey to track surface drainage system and relevant solid filler. -The large torrential stream (korongo) on the left side of the watershed drains into a lateral korongo thatdoes not feed the potential storage area.

Fig. 5 – Engutukoit dam

c) Baboon cave (Fig. 6):

Located just upon the Engutukoit dam and there are 5 micro dams (stones and concrete) which were builtduring colonial era. The highest one was used for human drinking, the second one for small ruminantswatering, the third and fourth ones are for big ruminants watering, the fifth one is for multiple use for bothhuman and animal watering. The entire dam is completely silted. The community has however attempted to desilt the dams and restorethe storage facilities by mobilizing their own resources and energy. The following actions are recommended:-Control/reduce upstream siltation -Erect a series of gabions upstream-Sedimentation chamber to be studied after a detailed topographic survey.

Fig. 6 – Baboon cave

GPS survey to determine the watershed limits over the 5 selected sites:

Purpose: an initial GPS survey along the watershed basins’ borders aims at precisely drawing the catchmentarea and therefore calculating the size. The extent of the watershed basin is directly correlated to thequantity of water that can be accumulated downstream and thus to the potential storage capacity. Bycalculating the evapotranspiration and infiltration in a determined area, the runoff that may be collected ina specific location can be subsequently estimated. The surveys have been undertaken at mid/end-August.

Methodology:

Tools and layers to be available:- Tablet with GPS and Locus free software, Garmin GPS for the field GPS survey- Qgis 2.x - Google Earth- Administrative boundaries layer- Water network (lines shapefile)- Channel network created through the specific SAGA function (using the “Filled DEM” and

”Catchment area”)- Contour (10m as interval between the contour lines) derived from the Digital Elevation Model

(DEM). The source is the of the raster files is the U.S. Department of the Interior- U.S. GeologicalSurvey http://earthexplorer.usgs.gov/ or ASTER Digital Elevation Model (Ministry of Economy, Tradeand Industry of Japan (METI) http://gdem.ersdac.jspacesystems.or.jp . In this case the former hasbeen used. Starting from the DEM, the “Filled DEM” (Fill sinks-SAGA) has been produced to reduceerrors and avoid empty spaces with the creation of the channel network

Outputs: - Watershed basins layer (Polygon)

The watersheds’ limits have been outlined through the use of GPS devices, such as Tablets or Garmin GPS(the Garmin GPS has been used as a backup in case of mistakes or any problem raised with the Tablet).Locus free is the software commonly adopted for the collection of GPS points or tracks on Android Tablets.Tracks corresponding to the watersheds limits have been recorded and subsequently transferred to Qgisin .gpx and to G. Earth in .kmz to check the accuracy of the line and make necessary corrections.

More in detail the following methodology has been adopted:

- Meet the representatives of the local community and understand through the local knowledgewhere the water flows during the rainy season. This is of fundamental importance to maintainthe momentum and keep the local community constantly engaged. The understanding of wherethe water streams according to the local community representatives and the coverage of thewatershed basin through a participatory mapping exercise (Fig. 7) has been undertaken fromthe one hand to benefit of the local knowledge and on the other hand to reinforce theownership of the intervention since the very beginning. The representatives have beenconstantly involved during the full field survey;

- Conduct a first screening of the territory potentially enclosed within the watershed. This hasallowed to understand at first sight the size of the territory interested by the survey andtherefore avoid as much as possible mistakes in tracking the limits;

- Track the border of the watershed with a Garmin GPS and the tablet device, using Locus freesoftware;

- Take note of the errors made during the survey for the sub-sequential correction in Qgis and/orGoogle Earth;

- Transfer data collected through the GPS to Qgis (.gpx format) and Google Earth (in .kmz). Inmany cases the mistakes made on the ground have been corrected through the Contour in Qgisand the aerial photography support in Google Earth or by visual detection and further gatheringof GPS points. This procedure has been applied also in case of unfeasibility of delimiting thelimits on the ground for terrain constraints (such as presence of impenetrable vegetation orborders possibly leading to situations of potential conflict);

- Polygonize the tracks to obtain watersheds (Geometry tools lines to polygons).

Fig. 7 – Participatory mapping exercise

Results: the 5 selected micro-watersheds (Tab. 2; Fig. 8) have been outlined in Qgis. One of them presentsthe characteristics of a larger watershed (Baboon Cave) with an extent of more than 14 Km 2 (see tablebelow). A comparison with the watersheds previously drawn was made and findings say that some

watersheds present substantial differences which confirms the difficulties in understanding small basinssecondary or tertiary order drainage streams, as well as the morphology of the terrain.

Tab. 2 – Area of the watersheds for the 5 selected sites

Fig. 8 – 5 selected sites

Name Area (Km2)Lemanda1 0.13Lemanda2 0.23Esilalei dam 0.31Engutukoit (colonial) dam

1.25

Baboon cave dams 14.65