Environment And Water Management

Preface

The Sustainability of the environment and water availability for domestic, agriculture and livestock water supply in the near future presents a great challenge and opportunity for all the dryland communities in Kenya and Somalia. They must play a fundamental role in environmental conservation and creating and maintaining access to and availability of this scarce resource for present and future generations. This would effectively improve environmental sustainability and agricultural and livestock productivity and significant improvements in the livelihoods of the local communities.

The challenge has been heightened, as problems with environmental degradation and freshwater quality and availability have multiplied and changed in response to growing population and economic activity over the past several decades. Adequate tree products and water supplies to meet basic human needs are essential to maintain and enhance the livelihoods of all the inhabitants of the two countries. For future generations, additional concerns will be to ensure adequate integrated resource management, ecosystem stability, water supplies and preservation of the quality of the environment, in addition to achieving greater equity in the distribution of natural resources (land and water) throughout the countries.

The key drivers of change that will impact future environmental management and water availability include: macro-environmental factors that create the broad context for development; and micro-environmental factors that affect particular elements of the agro-hydrologic system. All these factors interact and influence each other within the system/scenario. Future environmental management and water availability scenarios will be influenced by the following drivers: (1) demographic - population structure, population growth, urbanization and associated water demands, pressures of industrialization and migration within the two countries; (2) technological – environmental and land use technologies, information technology, biotechnology, renewable energy technologies (i.e. hydropower generation), water use efficiency, water pollution, new drought/pest/salt-resistant crops, sanitation, desalination; (3) social - lifestyles and cultural preferences, poverty, economic inequality;(4) environmental - committed to future climate change, water-related diseases, salinization, exhaustion and pollution of surface and groundwater, integrity and health of aquatic ecosystems; (5) governance - institutions, legislation, market dominance, power structure, conflicts, globalization.

Access to natural resources (land and water) in the two countries will significantly be influenced by actual availability, access policies, available infrastructure and institutions. Successful interventions will be introduced under enabling conditions for environment and agriculture. These enabling conditions that are elaborated upon include: appropriate environment and land use policies; focus on smallholder conservation agriculture; an integrated water resources management policy; promotion of public and private partnerships; adoption of international water initiatives; and legislative and regulatory framework. Future options of integrated water resources management for agriculture and livestock production will include: water resources management planning; adapting water resource management to climate change; response to key drivers of change; an integrated watershed management approach; rainwater harvesting and conservation for sustainable agriculture; and drip irrigated agriculture.

Prof. Elijah K. Biamah

Professor of Environmental and Water Systems Engineering,

School of Engineering, University of Nairobi, Kenya.

Chapter One

1.The Drylands Environment in Kenya

1.1Country Background

1.1.1Resource Exploitation

The scope of expanding cultivated land in high/medium rainfall areas(about 20% of total land area), is rapidly diminishing due to population pressure and ongoing fragmentation of land. Besides land fragmentation, population pressure has led to soil exhaustion, widespread encroachment into steep (>55% slope) water catchment areas and riverbanks. The intensification of farming practices in these high/medium rainfall areas and consequent soil degradation have limited the scope for increased agricultural productivity. Thus as arable land becomes limited and scarce in these areas, the tendency now is for landless people to move, settle and eventually develop new cultivable lands in marginal rainfall (ASAL) areas. This movement of people into the marginal land(approximately 72% of total land area) has brought into production these arid and semi arid lands so as to meet the food and fibre requirements of the ever increasing human and livestock population.

More of the landless people settling in ASAL have contributed significantly to the destabilization of ASAL’s fragile ecology through wrong technological transfer(e.g continuous cultivation of rangelands) and overstocking (higher than recommended land carrying capacities). These bad land management practices have accelerated the processes of soil erosion/degradation through overgrazing, faster rates of soil fertility depletion (by erosion and continuous cultivation), destruction of soil structure (of sodic/saline soils), increase in pests and diseases and other forms of degradation.

1.1.2Climate and Agro-climatic Zones

The seasonal rainfall patterns in Kenya are governed by the seasonal shifts and intensity of the low pressure Inter Tropical Convergence Zone (ITCZ). The mean annual rainfall ranges from about 250 mm in the northern areas to more than 2500 mm in the highlands. The areas of Kenya that receive 1000 mm or more of rain per year are restricted to the coastal belt, the highlands east and west of the Rift Valley and isolated hills (e.g Taita Hills). Rainfall occurrence is primarily bimodal with two distinct rainy seasons, long and short rains from March to May and October to December respectively. Arid and semi arid areas(ASAL) receive average annual rainfall of 200 to 900 mm. The short rains account for about 65% of the total annual rainfall. Potential evaporation ranges from 1450 to 2200 mm. The rainfall though low and erratic, occurs in high intensities of short duration and is highly erosive. High amounts of runoff are often generated from these storms due to inherent low infiltration rates of the soils. Concentrated runoff flows are responsible for the severe erosion that occurs in these marginal rainfall areas.

Figure 1.1 Agro-climatic Zones of Kenya.

All climatic elements, whether singly or in combination, affect crop and livestock production. The climatic elements of greatest significance to agricultural production in Kenya are rainfall, temperature and evaporation. On the basis of a relationship between rainfall and evaporation, Kenya is divided into seven Agro-climatic Zones(ACZs) based on the r/Eo ratio, where r is average annual rainfall and Eo is average annual potential evaporation in mm(see Figure 1.1). Nearly half of Kenya consists of zone VII(very arid) and nearly 2/3 of the country consists of zones VI and VII(arid to very arid). The agriculturally potential areas (zones I,II,III and some parts of IV) make up about 20% of the total land area.

1.1.3Soil Types

Most of the soil types occurring in Kenya are well drained and deep and these include the nitisols, acrisols, luvisols, ferralsols, andosols and phaeozems(see Figure 1.2). The other soil types are shallow to deep, well drained to poorly drained soils and these include solonetz, solonchaks, regosols, luvisols and cambisols. The most dominant soils in marginal rainfall areas are Luvisols, Acrisols and Vertisols. Except for the Vertisols, the other two soils are characterized as shallow soils with inherent low organic matter, water retention capacity, salt and sodium content and strong surface sealing and crusting properties. The dominant clays of Luvisols/Acrisols are usually of the 1:1 ratio (Kaolinite). Water infiltration in the soils is rather low especially in the B horizons where the textures are heavy. The management of these soils requires deep ploughing (to break the crust and subsoil hardpans) and addition of organic matter content from residue mulch or organic manure. Luvisols/Acrisols are often cropped during the rainy season. Vertisols are characterized as deep soils having moderate to high salt and sodium content, montmorillonitic (2:1) clay mineralogy, and low infiltration rates (due to swelling when wet). Structural tillage practices are not feasible on Vertisols due to their unstable structure (2:1 clays). Vertisols, due to their swelling and shrinking properties, affect crop root development when dry and infiltration when wet. These soils are workable immediately after the rainy season (under optimum soil moisture conditions) when the soils are loose and crumbly and hence requiring low draught per unit area. Vertisols are usually cropped after the rainy season.

Figure 1.2 Generalized Soil Types in Kenya (after Sombroek 1980, Muchena, Mbuvi and Wokabi, 1988).

Overall, tillage management requirements of these three soils would depend on clay mineralogy, workability, moisture holding capacity and other soil characteristics. Luvisols/Acrisols have a compact subsoil layer (argillic horizon) due to an increase in clay content from A to B. These soil problems (especially the sealing and crusting) are known to affect seedling emergence, decrease rain infiltration and consequently result in high surface runoff rates (with minimal soil loss unless the soils are disturbed and have a cloddy top soil structure).

1.1.4Resource Degradation

Soil erosion and degradation in Kenya is a widespread problem threatening the sustainability of agricultural productivity and causing the deterioration of both land and water resources. The severity of this problem is more pronounced in arid lands (especially on grazing lands) where high rainfall intensities of short duration, susceptibility of the soils to erosion (due to a low organic matter content) and human mismanagement of land (through overgrazing, bush clearing and charcoal burning) have accelerated and magnified soil losses by erosion and consequently reduced crop yield potential.

The onset of degradation in arid lands areas is attributed to various factors such as long and severe droughts, heavy rains and floods, locust infestations, overgrazing, deforestation and over-cultivation.

The assessment of soil erosion (due to uncontrolled grazing and overgrazing) in arid lands and subsequent classification of its severity, manifests itself in erosion features such as severe sheet erosion, scattered dendritic rills, gullies, riverbank erosion and wind erosion. Due to the exposure of poor subsoils, the degraded areas have a low capacity of regeneration of herbaceous vegetative cover. With the resultant erosion of nutrient rich topsoil, the remaining subsoil cannot support the establishment of any grass or vegetal cover. Worse still some of the shrubs like Acacia reficiens are known to inhibit any other vegetative growth underneath. The lack of ground cover coupled with the high rainfall intensities and high susceptibility of the soils to erosion, have accelerated the processes of soil detachment and sediment transportation. The transported nutrient rich soil is deposited along the floodplains.

Besides reducing the crop yield potential of the arid lands soils, soil erosion also results in high sediment yields from watersheds and could result in siltation of water retention reservoirs such as dams and lakes.

1.1.5Resource Conservation

The primary objective of resource conservation efforts in arid lands of Kenya is to conserve soil, water, forest and rage resources. These efforts while addressing themselves to soil and water conservation, fuelwood and fodder production, water resources and livestock development, and range management, require integrated land use approaches that are acceptable to the local people. Fodder production and water conservation are priorities that require immediate consideration due to the prevailing aid lands conditions and pastoral background of the people.

Current attempts to reduce soil erosion and degradation include the catchment(watershed) approach to soil conservation, gully stabilization, terracing, tree planting(for fuelwood and fodder), range reseeding and rainwater harvesting in dams and waterpans. These efforts have helped to minmize in situ detachment of soil particles and hence the loss in soil productivity. Production of grasses like Makarikari, Eragrostis superba and Cenchrus ciliaris and trees like Leucaena leucocephala and Prosopis spp have proven successful in providing fodder and fuelwood and minimizing soil erosion and degradation.

1.1.6Cropping Systems

Agricultural cropping systems in Kenya vary widely, reflecting both the range of agroclimatic zones and the variety of land ownership patterns. The major cash crops are coffee and tea. Other cash crops are pyrethrum, cotton, wheat, barley, sunflower, sugar, sisal, groundnuts and fruits. The staple food crops are maize, beans, sorghum, millet, cassava, pigeon peas, sweet potatoes, and cowpeas. Crop performance and yield are significantly influenced by the amount of rainfall and distribution throughout the rainy season and soil conditions. Where soil conditions and rainfall are limiting (e.g ASAL) there are inherent soil moisture deficits which confine the period of cropping to the rainy season. The potential length of growing season as determined by the long and short rains influences the choice of crops in these areas. Most crops are grown during the short rains since more rainfall occurs within this period. Intercropping is a very common farming practice as it minimizes the risks of crop failure due to unexpected soil moisture deficits. Usually combinations of two or three crops are evident in most of these areas.

1.1.7Land Productivity

During the past two to three decades, human and livestock population in Kenya has significantly increased and consequently led to an over exploitation of the limited land and water resources especially in ASAL. In ASAL areas, soil and vegetative degradation have become widespread due to overgrazing, deforestation, burning and over cultivation. Accompanying this unprecedented population increase, is the fragmentation of landholdings and sedentarization of pastoralists which has destabilized the very fragile ecology of the areas. This has adversely affected food and fodder production and left the entire population vulnerable to food and fibre shortages. Unpredictable weather conditions have exacerbated the problems and further eroded the production potential of the shrinking resource base.

Chapter Two

2.Conservation Technologies for Agricultural Watershed Management in Kenya

2.1Management of Agricultural Watersheds in Kenya

The management of agricultural watersheds in Kenya requires prioritization of problems and technological options on the basis of prevailing environmental degradation problems. The major environmental degradation problems that have decreased productivity of agricultural watersheds include: severe soil erosion, excessive waterlogging or flooding, low soil moisture, low soil fertility and increased soil crusting, soil compaction, and sedimentation. The occurrence of these problems is known to cause ecological degradation, agricultural drought, low crop productivity and poor water quality within a watershed.

At the field (micro) scale, the farmer’s plot could be viewed as under cultivation or grazing; and with or without erosion control measures in place. The plot under cultivation and with erosion control measures in place, could be considered as the micro scale agro-hydrologic system that is of major concern to agricultural production and hence should be given priority in the mitigation against seasonal agricultural drought and soil erosion. Spatial and temporal variabilities in soil moisture within homogenous areas of micro scale significantly influence the productivity of a farm. In order to tackle this problem of low soil moisture, due consideration must be given to the physico-chemical properties of semi-arid soils. Other soil characteristics of significance to rainwater infiltration include organic matter content, soil bulk density, and the silt/clay ratio. Hence there is a need to understand how soil micro-topography (cloddiness or surface roughness), soil aggregation, soil compaction and surface soil crusting influence infiltration, runoff and erosion. Of significance is the plot’s response to tillage and residue management techniques such as conventional tillage, zero tillage, residue mulching, tied ridging and farmyard manure application. These soil and water management techniques introduced should improve soil surface conditions by enhancing rainwater infiltration through surface storage of overland flow; and increase the tillage depth and hence the crop rooting zone for conservation of soil moisture. The seasonal trends in profile soil moisture under these practices would show whether the moisture available would be adequate for crop production.

At the watershed (meso) scale, the area between the topographic divide (ridge) and the valley (drainage way) is the meso-scale agro-hydrologic system that is ideal as a conservation planning unit. The planning involves some thorough evaluation of erosional hazards of land use, the effectiveness of rainfall and the capability of the soil to sustain crop growth and improve yields. Depending on the soil type and extent of soil and vegetation degradation, up to 70% of rainfall may be lost as surface runoff from a watershed. The rate at which surface runoff occurs in a given area is dependent upon causative and conditioning factors. Causative factors include rainfall intensity and duration, frequency of occurrence of storms, and the size of watershed. Conditioning factors include those that affect infiltration rate and time of concentration. Soil type, vegetative cover, and antecedent soil moisture and storm duration govern infiltration rate. The time of concentration depends on the area, slope and stream pattern within a watershed. Thus the infiltration rate and time of concentration are significantly influenced by the given watershed characteristics. In order to design effective soil and moisture conservation systems for agricultural watersheds, an essential prerequisite is the application of scientific principles to predict infiltration, runoff, and profile soil moisture from the dominant soil types. In Kenya, a lot has been done in the areas of soil conservation, rainwater harvesting and conservation for crop and fodder production without some proper understanding of the hydrologic processes that influence the applicability of moisture conservation practices and hence leading to an increase in crop and biomass yields.

This Chapter has attempted to develop that understanding of rainfall-runoff processes and soil moisture dynamics and subsequently established criteria to be used in prioritizing soil and moisture conservation measures. Some thorough understanding of rainfall-runoff processes and soil moisture dynamics is necessary for there to be some meaningful scientific strides in recommending soil and water management practices for specific agricultural watersheds in Kenya.

2.2Watershed Management Strategies in Kenya

2.2.1Assessment of Resource Degradation

Changes in land use patterns on croplands and rangelands have significantly accelerated the process of soil and vegetation degradation in agricultural watersheds in Kenya. In Kenya, watershed resource degradation is a widespread problem that is threatening the sustainability of agricultural productivity and causing the deterioration of both land and water resources. The severity of this problem is more pronounced in agricultural watersheds (especially on grazing lands) where high rainfall intensities of short duration, susceptibility of the soils to erosion (due to a low organic matter content) and bad land use practices (through overgrazing, deforestation, over-cultivation) have accelerated and magnified soil losses by erosion and consequently reduced land productivity. crop yield potential.

The onset of watershed degradation in Kenya is atttributed to various manmade and environmental factors such as long and severe droughts, topography (rugged and steep slopes), soil erodibility (due to structural instability of soil aggregates), rainfall erosivity (due to heavy rains and floods; high rainfall intensities of short duration), pest infestations (e.g. army worm, locust, white grub and termite activity), soil degradation (due to overgrazing, deforestation, over-cultivation, mass movements and tunnel erosion).

The assessment of soil erosion in agricultultural lands and subsequent classification of its severity, manifests itself in erosion features such as sheet erosion, scattered dendritic rills, gullies, riverbank erosion and wind erosion. Due to the exposure of poor subsoils, the degraded areas have a low capacity of regeneration of herbaceous vegetative cover. When nutrient rich topsoil is eroded, the remaining subsoil cannot support the establishment of any grass or vegetal cover. The lack of ground cover coupled with the high rainfall intensities and high susceptibility of the soils to erosion, have accelerated the processes of soil detachment and sediment transportation. The transported nutrient rich topsoil is deposited along riverine floodplains.

Besides reducing the crop yield potential of upland soils, soil erosion interferes with the microclimate of agricultural watersheds (as influenced by the hydrologic cycle) and results in high sediment and runoff water yields. This watershed degradation causes problems of siltation of water retention reservoirs such as dams and lakes; diminishing groundwater supplies (due to high surface runoff and low rainwater infiltration rates); and poor surface and groundwater quality (due to suspended and dissolved solids).

2.2.2Slope-based Production Zones

The management of agricultural watersheds in Kenya requires some clear understanding of the four major land management problems influencing agricultural productivity namely: severe soil erosion, low soil moisture, low soil fertility and increased soil crusting and compaction. The occurrence of these problems on croplands and rangelands is significantly influenced by factors such as climate, soil type, land use (especially tillage practices), erosion control measures and slope. Slope is the single most important factor upon which these four problems are clearly stratified for purposes of identifying appropriate soil, water and nutrient management interventions. The slope based differences in watershed management can be broadly categorized into three distinct production areas or zones namely: uplands slopes zone(hilly and gully area); midlands slopes zone(gully-plateau area); and lowland slopes zone(plain-flat area).

Upland Slopes Zone(> 47%)

This area represents the zone of no erosion and is characterized by steep slopes and is dissected by deep watercourses. In the past, this area was under forest and permanent vegetation. However due to expansion of cultivated lands, this area is now prone to severe soil erosion due to deforestation. This zone often has no erosion control measures in place. Depending on the soil type and extent of vegetation degradation, this area would generate very high amounts of surface runoff. The erosion of fertile top soil would lower the fertility of the soil. Likewise the low rainwater infiltration and high evapotranspiration rates would lower the availability of soil moisture within the crop rooting zone.

In this zone, soil erosion could be prevented by practices such as: construction of gully head dams in valley bottoms; construction of terraces especially excavated bench terraces and contour ditches depending on soil depth and slope. Agronomic practices such as grass, unploughed, and sisal strips could be applied where appropriate.

Figure 2.1. Slope-based stratification of soil, water and nutrient problems in agricultural watersheds (Biamah and Oduor, 1999).

Midland Slopes Zone(12%-47%)

This area represents the zone of active erosion and is characterized by lands under cultivation. However, where crop cultivation is common and erosion control measures are in place, there is minimal soil erosion. But surface runoff would continue to be generated and safely disposed off through waterways. So soil erosion and soil moisture are