Application Of GIS In Assessment Of Land Suitability For Irrigation Methods

Introduction

This chapter briefly gives the general information relevant to the research of irrigation capability for different irrigation methods in a catchment. It shows how research will reduce the problem through achieving different objectives.

Background of the study

Irrigated land produces 40% of global food (IFAD, 2015). Currently, Uganda’s ratio of cultivated area under irrigation to the irrigation potential is only 0.5%. This compares lowly to 3.6% for Tanzania, 2.0%for Kenya and 1.6%for Burundi. The comfort of receiving rains to sustain two cropping seasons in a year has provided little impetus to the Government to invest extensively in irrigation. Little attention has been accorded to technological and human capacity development in irrigation. Despite the advantages that the country holds in the ease of undertaking irrigation development, the potential has not been harnessed. Uganda’s rain-fed agriculture has progressively been constrained by frequent threats of, and actual occurrence of, droughts and floods affecting efforts for increased production; fight against hunger and poverty. Uganda’s vulnerability to climate change is exacerbated by a rapidly growing population, a factor that has increased pressure on natural resources (mainly wetlands and forest covers) leading to environmental degradation.

The gradual impacts of climate change and population pressure on land use are beginning to have a remarkably adverse impact on agricultural productivity in particular and on the entire economy as a whole. In 2010, alone, drought accounted for 38% and 36% loss in production for beans and maize respectively. In 2014, the country registered Uganda shillings 2.8 trillion (8%) loss of Gross Domestic Product (GDP) and 87% loss to agro-industries (Mwaura et al 2014). These conditions translate into the country’s food consumption gaps, high Global Median Acute Malnutrition (GAM) rates, with many people marginally able to meet their minimum food needs especially during dry spells (NAP-Ag report, 2017). In 2011 alone, the Department of Disaster Management of the Office of the Prime Minister estimated the damage and production losses as a result of climate change at UGX 4.3 Trillion which translates to about 7.5% of GDP.Uganda has one the highest irrigation potential in the world with over 15% of her surface area covered by freshwater resources. The sum of the external and internal renewable surface water resources (the average annual river flow generated from precipitation) in Uganda amounts to 43.3 billion cubic meters per year, while the dependence ratio (proportion that originates outside the country) was about 69% as of 2013. The present utilization rate of the internal renewable water resource is low (2.8%). The utilization rate of the entire renewable surface water resources stood at 0.01% as of 2013. If the full irrigation potential was to be exploited, the demand for water would be increased by over 400% by 2030 translating into a utilization rate of renewable surface water resources of 0.05%.

Aware of both the challenges and opportunities, there’s need for the direct siting and implementation of irrigation schemes in the different parts of the country to ensure optimal use of available land and water resources for agricultural production and productivity to contribute effectively towards food security, wealth and employment creation, and export promotion. This is in line with Uganda’s international commitments including the Sustainable Development Goals, and Agenda 2063 as well as the Vision 2040 notes that: “Uganda aspires to transform agriculture from subsistence to commercial agriculture through both mechanization and introduction of modern irrigation systems''.

Problem statement

The Malaba River supplies the bulk of the water demands of the region. The application of irrigated agriculture has been embraced at a lesser extent in the study area. Currently, the irrigation systems used by farmlands in the region are furrow irrigation, basin irrigation and border irrigation schemes. The use of surface irrigation systems has been applied specifically for rice and maize, to meet the water demand of both wet and dry seasons. But due to the depletion of water resources and the increase in the population, the extent of irrigated area per capita is declining which calls for investigation of the capability of the area for more water efficient irrigation methods so as to improve productivity.

Main objective

Apply GIS in assessment of the land suitability for surface, sprinkler and drip irrigation.

Specific objectives

1. To delineate the watershed along R. Malaba and characterize its soils
2. To calculate the capability index.
3. To develop and collate the suitability maps.

Purpose of study

The purpose of the study is to investigate the land suitability depending on it the physical and chemical properties for different irrigation so as to improve crop production as a way of ensuring food security in the region

Justification

This study will help in;· Knowing the appropriate irrigation for a particular area which will guide the government and private sector in choosing the right method for improved productivity.· Use of GIS provides relatively cheaper and faster suitability analysis.

Scope of the study

This study will be limited to only the land capability for irrigation methods of River Malaba catchment. It will focus on the analysis of specific datasets such as climate data (rainfall temperature and wind velocities), land cover data, catchment characteristics, topographic data and soil data to provide geo-referenced map of two resources (water and land resources) and classify the catchment per given irrigation method among for future planning and development possibilities.

Literature review.

This chapter covers relevant literature on the different types of irrigation with much emphasis on their land suitability. And all is guided by the problem statement and objectives of the study.

Geographic Information system (GIS).

Geographic Information system (GIS) is a computerized system that is used to capture, store, retrieve, analyze, and display spatial data (Clarke 1995). GIS is “an information system that is designed to work with data referenced by spatial or geographical coordinates” (Star, 1990). Geographically referenced data are data that describe both the locations and characteristics of spatial features such as roads, land parcels, and vegetation stands on the Earth's surface. GIS consists of five basic elements: “data, hardware, software, procedure and people” (Dangermond, 1988). GIS applications are tools that allow users to create interactive queries (user-created searches), analyze spatial information, edit data in maps, and present the results of all these operations.

Mapping

The main application in GIS is mapping where things are and editing tasks as well as for map based query and analysis (Campbell, 1984). A map is the most common view for users to work with geographic information. It's the primary application in any GIS to work with geographic information. The map represents geographic information as a collection of layers and other elements in a map view. Common map elements include the data frame containing map layers for a given extent plus a scale bar, north arrow, title, descriptive text, and a symbol legend.

Delineation of a watershed.

A watershed can be defined as the catchment area or a drainage basin that drains into a common outlet. Simply, the watershed of a particular outlet is defined as an area, which collects the rainwater and drains through gullies, to a single outlet. Delineation of a watershed means determining the boundary of the watershed i.e. ridgeline. GIS uses DEMs data as input to delineate watersheds with integration of Arc SWAT or by hydrology tool in ArcGIS spatial analysis (Winchell et al., 2008).

Remote sensing.

Remote sensing is the examination or gathering of information about a place from a distance. Such examination can occur with devices like cameras based on the ground and/or sensors or cameras based on ships, aircraft, satellites or other spacecraft. Remote sensing is the acquisition of information about an object or phenomenon without making physical contact with the object and thus in contrast to in situ observation. (Robert, 2007) Remote sensing plays a significant role in GIS. Its images are used as the input data for the raster-based digital elevation models (DEMs) a common type of data used in GIS. The air photos taken during remote sensing applications are also used during GIS digitizing to create polygons, which are later put into shape files to create maps. Applications of remote sensing range from the use of orthoimagery as a GIS base layer, to the development of thematic data on land use and the generation of unique geospatial datasets via extraction of cartographic features such as buildings and roads from imagery. It may be split into active remote sensing; when a signal is first emitted from the aircraft/satellites (Schott and John Robert, 2007) or passive; when information is merely recorded.GIS as a tool for irrigation methods assessment

Irrigation in general

Irrigation is defined as the artificial application of water (on supplementary or complementary basis) to the soil for the purpose of supplying the moisture essential for plant growth. A broader and more inclusive definition is that irrigation is the application of water to the soil for any number of the following purposes.

• To add water to the soil so as to supply the moisture essential for plant growth (this is usually the main objective)
• To cool the soil and atmosphere thereby making more favorable environment for plant growth (using micro-sprinklers)
• To wash out or dilute salts in the soil (Leaching)
• To apply fertilizers or soil amendments. (Fertigation)

Types of irrigation

Irrigation is divided into three major types; surface irrigation, subsurface irrigation and pressurized irrigation. But for the purpose of this study only surface and pressurized irrigations will be covered.

Surface irrigation involves application of water to the land by an overland water flow regime. Within this type are;

• Borderline irrigation
• Furrow irrigation
• Basin irrigation

Pressurized irrigation also includes; Drip/ localized irrigation. Sprinkler irrigation Irrigation methods Suitable crops Suitable soils Slope Water availability Advantages Disadvantages Watering bucket Horticulture Most soil types Relatively flat Applicable where water supply is unlimited Cheap, requires less land grading and levelling Labor intensive Basin Row field crops and horticultural crops Fine textured soils Relatively flat Requires large quantities of water and size depends on water availability Good control of large flows. Can be used to leach out salts. May require land grading and levelling, hence costly Furrow Row field crops and horticulture Most soil types Very gently sloping and slopes less than 2% Requires large quantity of water Permits irrigation of large fields Difficult to achieve uniform water application Sprinkler Most crops except rice Light textured and highly permeable soils Wide range of slopes Applies in areas with limited water supply Highly efficient and can be applied in areas with limited water supply High installation costs and requires skill in operation and management Drip Trees and low-density crops A wide range of soil types Wide range of slopes Areas with limited water supply Efficient water use High initial cost

Sprinkler irrigation

Sprinkler irrigation is a method of applying irrigation water to the soil that tries to mimic natural rainfall. Sprinkler irrigation comprises a set of equipment which include sprinklers, risers, laterals, sub-mains, main pipelines, pumping plants and boosters, operational control equipment and other accessories required for efficient water application. In some cases, sprinkler systems may be pressurized by gravity and therefore pumping plants may not be required.

Drip irrigation

This is also called trickle irrigation; the water is led to the field through a pipe system. On the field, next to the row of plants or trees, a tube is installed. At regular intervals, near the plants or trees, a hole is made in the tube and equipped with an emitter. The water is supplied slowly, drop by drop, to the plants through these emitters.

Components of Drip irrigation system

Head unit: This contains filters to remove debris that may block emitters; fertilizer tank; water meter; water pump units; or water tanks and pressure regulator.Mainline, Laterals, and Emitters which can be easily blocked in case water contains debris.

Control Head Unit

Control Head unitWetting PatternEmitterLateralMainline or manifold

Surface irrigation

Surface irrigation is the method of application of water to the land by an overland water flow regime. In surface (furrow, flood, or level basin) irrigation systems, water moves across the surface of agricultural lands, in order to wet it and infiltrate into the soil. Surface irrigation can be subdivided into furrow, border strip or basin irrigation. It is often called flood irrigation when the irrigation results in flooding or near flooding of the cultivated land. Historically, this has been the most common method of irrigating agricultural land and still used in most parts of the world.The field water efficiency of surface irrigation is typically lower than other forms of irrigation but has the potential for efficiencies in the range of 70% - 90% under appropriate management.

Irrigation Land Suitability Evaluation Factors

Land suitability is the fitness of a given type of land for a defined use. The land may be classified in its present condition or after improvements for its specified use. The process of land suitability classification is the appraisal and grouping of specific areas of land in terms of their suitability for defined uses (FAO, 1976). Land evaluation is primarily the analysis of data about the land – its soils, climate, vegetation, and etc. in terms of realistic alternatives for improving the use of that land. For irrigation, land suitability analysis, particular attention is given to the physical properties of the soil, to the distance from available water sources and to the terrain conditions in relation to methods of irrigation considered (FAO, 2007). In addition to these factors, land cover/land use types are considered as limiting factors in evaluating suitability of land for irrigation (Haile Gebrie, 2007). As extensively discussed in FAO land evaluation guidelines (FAO, 1976, 1983, 1985), the suitability of these factors for surface irrigation method and for the given land utilization types can be expressed corresponding to the following suitability classes. Order S - suitability. The classes under this order are:

• S1 (highly suitable) - land having no significant limitation to sustained application of a given use.
• S2 (moderately suitable) - land having limitation which in aggregate are moderately severe for a sustained application of a given use.
• S3 (marginally suitable) - land having limitations which in aggregate are severe for a sustained application of a given use and will reduce productivity or benefits. Order N suitability classification
• N1 (temporarily not suitable) - land having limitations which may be surmountable in time but which cannot be corrected with existing knowledge at currently acceptable cost.
• N2 (Permanently not suitable) - land having limitations which appear as severe as to preclude any possibilities of successful sustained use of the land of a given land use.

The factors considered for surface irrigation land suitability evaluation are narrated separately in subsequent sub-sections.

Methodology

This chapter addresses the methods and techniques that will be used to achieve the stated objectives for the land evaluation research along the river Malaba.

Objective One

To delineate the watershed along R. Malaba and characterize its soils The hydrological characteristics of the river during the dry season will be studied, in which the rainfall, temperature and discharge data will be obtained. This will help in obtaining the crop water requirement and the probable area that can be irrigated. Through use of ILWIS and Arc view GIS soft wares improved with google earth aerial land map will be delineated or extracted for the water shed further development.With the guide of the developed map, a field survey will be conducted. Profile pits will be opened in the land unit from which different soil samples will be extracted and taken to the laboratory for testing. The land evaluation will be determined, by parametric method, based upon topography, and soil characteristics. The land is evaluated according to numerical indexes. In this classification system, firstly a degree, whose rate is from 0 to 100, is given to any land characteristic through comparing them with the tables of soil requirements. The specified degrees are used in order to measure the land index that is a multiplicative index that combines ratings assigned to soil map units and other physical conditions that affect the land use (Olson, 1981). The topography characteristics included slope while soil properties included soil texture, depth, salinity, drainage and carbonate content. Also, soil properties such as Cation Exchange Capacity (CEC), organic matter (%OM) and pH are considered in terms of soil fertility (Sys et al.1991).

Objective Two

To calculate the capability indexThe parametric evaluation approach will be employed. The above characteristics of slope, soil texture, soil depth, salinity, drainage and carbonate content will be considered.· Soil texture: rated taking in account the permeability and available water content, and calculated, as weighted average, for the upper 100 cm.· Soil depth: rated with regard to the thickness and the characteristic of the soil layers (horizons).· Calcium carbonate content: influencing the relationship between soil and water, and the availability of nutrient supply for plants (150 cm of soil profile). It is rated with regard to the CaCO3content effect on soil profile.· Salinity: rated on the base of the electrical conductivity of soil solution.· Drainage, visually estimated during the fieldwork, is indicated with a code that gives it a qualitative characterization.· Slope, in %, was measured using clinometers.Rates are assigned to the aforementioned six parameters as per the related tables, thus, a capability index for irrigation (Ci) will be developed as shown in the equation below: Where Ci = capability index for irrigation; A = soil texture rating; B = soil depth rating; C = CaCO3 status; D = electro-conductivity rating; E = drainage rating; F = slope rating. Suitability classes are defined considering the value of the capability index Table1 Suitability classes for the Irrigation Capability Indices (Ci) classes

Objective Three

To develop and collate the suitability mapsIn order to develop land suitability maps for different irrigation methods, a semi-detailed soil map will be prepared, and all the data for soil characteristics will be analyzed and incorporated in the map using ILWIS software. The digital soil map base preparation will be the first step towards the presentation of a GIS module for land suitability maps for different irrigation systems. The Soil map will then be digitized and a database prepared. Different polygons or land mapping units (LMU) will be determined in the base map. Soil characteristics will also be specified for each LMU. These values will be overlaid to generate the land suitability maps for surface, sprinkler and drip irrigation systems using Geographic Information Systems.

Expected results, Work plan and Budget

This section details the expected results of the project, the activity schedule for the project and the estimated cost of the project

Expected results

At the end of the project, the following results will be achieved:

Work plan

Activity 2018 2019 Aug Oct Nov Dec Jan Feb Mar April May

Topic identification Literature research proposal writing consulting the supervisor proposal presentation Data collection Data analysis Report writing Project presentation

Conclusion

The implementation of the project “application of GIS in assessment of land suitability for different irrigation methods; surface, drip and sprinkler methods” will ensure a sustainable use of land and water resources. This will guide the government and different stakeholders in construction of the appropriate irrigation schemes in the zone.