«BY ROICK CHIKATI (R035991L) SUPERVISOR: Dr. A Senzanje An undergraduate Research project submitted in partial fulfilment of requirements of the ...»
QUANTIFYING THE WATER IN SILTED UP SMALL DAMS AND
ESTABLISHING HOW IT CAN BE ABSTRACTED FOR HUMAN
LIVELIHOODS: A CASE OF MZINGWANE CATCHMENT.
ROICK CHIKATI (R035991L)
SUPERVISOR: Dr. A Senzanje
An undergraduate Research project submitted in partial fulfilment of requirements of the
Degree of Bachelor of Science Honours in Agricultural Engineering
Department of Soil Science and Agricultural Engineering University of Zimbabwe P.O. Box MP 167 Mt Pleasant Harare July 2007 1 Acknowledgements Thanks to the Almighty for keeping me all the way through the study and for giving me the strength and courage. Thank you dear Lord.
I wish to express my sincere gratitude to the following:
Dr A Senzanje, Deputy Dean of Faculty of Agriculture, my project supervisor, for his diligent guidance, constructive criticism, and careful reading and correction of the manuscript.
Special regards go to Mr Chitopo, Mr Ncube and to my two sisters Chipo and Sifiso. To Muchaneta, I say long live. To my classmates, friends and family, God loves you all.
Alluta continua, viva VaMatema. To Charlie I say thanks man.
TABLE OF CONTENTSAcknowledgements
1.2.1 Main objective:
1.2.2 Specific objectives:
2.0. Literature Review
2.1. Background and development
2.2. Water resources assessment in Zimbabwe
2.3. Socio-Economic Aspects.
2.4. Environmental Aspects
3.0 Study Area And Methods
3.1. Description of study area
3.2. The Limpopo River Basin
3.3. Mzingwane Catchment.
3.4. Majelimane dam
3.6.1 Estimating the amount of silt in Majelimane dam.
3.6.2. Measuring the moisture content
3.6.3.Estimating the water that can be abstracted
4.1. Results and Discussion
4.2. Measuring the moisture content of the silt
Table 4.3 Moisture content using Oven method
4.3. Quantifying the amount of water in the silt in Majelimani dam which can be abstracted.
4.4. Purposes of water from the silt of silted up small dam
4.5. Assessing how the water can be abstracted for use by rural people.
5.1 Conclusion and recommendations
1.0 Introduction The government of Zimbabwe (GOZ) directly facilitated the construction of small dams.
To date over 10 000 dams have been constructed in communal areas and the then larger scale commercial areas (Sugunan, 1997). Smaller dams are water storage structures whose capacity is less than 1 million cubic metres with a maximum height above a cleared foundation level which is less than 8m (Kabel, 1986). Smaller dams consist of vertical impermeable barrier through a cross section of a sand filled seasonal river bed.
Many smaller dams however are susceptible to siltation, therefore they accumulate much sand. Smaller dams are multipurpose structures whose use includes irrigation, livestock watering, brick making, domestic and recreation (Sugunan, 1997; Keller, undated). In view of the vast range of uses, smaller dams were developed to uplift people living standards mostly in communal areas.
Rural areas have frequently dry spells, therefore livelihood centred on agriculture production there are high population figures and least structural development (Zirebwa and Twomlow, 1999). Livelihood security, most significantly for poorer households, depends almost entirely on agricultural production and or exploitation of key local resources (trees, forest, arable land, streams, etc.). Given this dependency on natural resources, the barriers faced in production, and the ultimate objective of improving food security, any improvements to improving livelihoods (at least in the short term) must be based on sustainable optimising the potential of smallholder agricultural and to a lesser degree, livestock production (Jim Ellis-Jones and Zvarevashe; 2000).
In specific household context, one of the principle constraints to improving agriculture production is inadequate water resources. It is imperative to note that the capacity of smaller dams is variable both within and between seasons because of rainfall availability, evaporation, seepage and mainly of siltation accumulation. Most of reservoirs cannot store water from one season to another (Manzungu, 2002; Keller et al, undated). Most of 4 the dams in the Limpopo river basin do not store water from season to season because of high rates of siltation and sand accumulation in those small dams. Much of this water is understood to have be locked in the silt of these silted up small dams most rural people dug small wells in the mid points of these small dams so that they can
the water (Ogbeide, 2003) This project is being carried out in Matabeleland South (Gwanda). The much available water in most parts of Matabeleland is from surface runoff during rainfalls which is associated with high erosion of top soils, siltation of smaller reservoirs and gully formation. Therefore communal farmers in those areas generally lack reliable underground water resource and rely almost on surface water and occasionally on very low amounts of natural rainfall (Jim Ellis-Jones and Zvarevashe, 2000). This however means that in specific household context one of the principal constraints in improving agricultural production again is inadequate water resource that might have been locked in the silt of silted up small reservoirs. This brings the concept of trying to quantify the amount of water in the silt of silted up small reservoirs and establishing how this water can be utilised.
Livelihood embodies three fundamental attributes, the possession of human capabilities (such as education, skills, health and psychological orientation), access to tangible and intangible assets, and the existence of economic activities (Jim Ellis –Jones and Zvarevashe, 2000). These however are centred on the availability of essential water which however is mainly stored in smaller dams hence the need to study the smaller dams. Moreover despite the wide coverage accorded to larger dams in publications and research, little information is available on small dams (AREX report, 1997).
Communities that host small dams have risks imposed on them that sometimes they have failed to irrigate their gardens, use the water for domestic purposes since much of it is understood to have been locked in the silt of silted up small reservoirs (Ogbeide, 2003).
Smaller dams in (GWANDA) Agro ecological Region AER (1V) and (V) mostly dry up between May and November. It is again important to note that the Agro-ecological 5 Region (AER) (IV) and (V) covers up to 60% of the total area in Zimbabwe hence much agricultural activities are expected and centred in this area. These areas are dry and water remain locked in the silt of silted up dams that most farmers dig the wells in those sand and silt beds hence the need to devise methods which can be used economically to abstract th available water locked in silt for human livelihoods.
It is the aim of this study on small dams that try to measure, quantify and abstract water in silt of silted up dams (Case study on Majelimane small dam). It also aims to evaluate how it can be sustainable abstracted for rural livelihoods especially those in Matabeleland South Province in Gwanda (Avoca). This means the need to study the amount of water in the silt of small dams might be the answer in the development of rural livelihoods. How much water is in those silt, its recharge and the rate at which silt is accumulating is also major concern especially to the small dams’ users who derive their livelihoods on these small dams.
1.2 Objectives In light to address and find answers to these problems raised above regarding the abstraction of water locked up in the silt of silted up small dams and establishing ways in which it can be abstracted and used the following main and specific objectives were identified.
1.2.1 Main objective:
To quantify the amount of water in silt of silted up small dams and establishing how the water can be sustainable abstracted for rural people.
1.2.2 Specific objectives:
• To measure the amount of silt in silted up small dam.
To measure the moisture content of the silt.
• To quantify the amount of water in the silt of silted up small dam, that can be • abstracted (recharge) and match it with discharge.
2.0. Literature Review
2.1. Background and development Water resources are critical for improving rural livelihoods and their natural environment (Ellis-Jones and Zvarevashe, 2000). In addition, water is essential in maintaining the function of ecosystems and associated flora and fauna which humans depend on both directly and indirectly (Moyo, 1995). Zimbabwe is a semi-arid country with unimodal season which generally runs from mid November to early April averaging 650mm per annum (Senzanje and Chimbari, 2002). Rain season is mostly disrupted by protracted dry spells especially in the southern Zimbabwe. In communal areas (CA) of southern Zimbabwe the need for water is critical in maintaining and improving rural livelihoods.
The communal lands in Agro-ecological regions (AER) (IV) and (V) cover over 60% of the total land area of Zimbabwe (Jim Ellis Jones and Zvarevashe, 2002). These areas are being overgrazed, resulting in poor soil fertility together with limited rainfall creating conditions which severely restrict agricultural production (Moyo, 1995). These all promote excessive siltation and it accumulates in the several small dams around the Limpopo river basin. However in specific household context one of the principle constraints in improving agricultural production is inadequate water resource (Senzanje and Chimbari, 2000). This then brings forward the principal of trying to abstract the water locked in the silts of silted up small dams and establishing how it can be sustainable abstracted and used for the improvement of rural livelihoods. Small dams can be defined as an excavated water storage structure whose capacity is less than one million cubic metres and whose height above a cleared foundation level is bellow eight metres (Kabel, 1986)
2.2. Water resources assessment in Zimbabwe.
Approximately 10% of rainfall is lost as runoff in semi-arid areas of Zimbabwe (Mugabe et al, 2004). This runoff is sufficient to fill the small to medium reservoirs, on which rural communities depend on in most years except the very dry ones when there is little or no runoff. There is improper management of the water resources and in most cases crisis management is employed at last moment when shortages are apparent. According to Stevenson, 2000 water resources are critical for improving rural livelihoods and their natural environment. Crisis management includes bringing up methods that save water and also abstracting the water which could have been stored in the silt of these small dams. According to Zirebwa and Twomlow, 1999 more than 600 small reservoirs were constructed in drier parts of the country in the last 30 years and vary in capacity from 60 00 cubic meters to 30 00 cubic meters and catchment area of between 2square kilometre and 55 square kilometre. This study recognized the opportunity to use water from the silt of silted up small dams for community development.
2.3. Socio-Economic Aspects.
In water act of 1998, water use is classified as either primary or commercial. Primary being the reasonable use of water for sustenance of life i.e., not exceeding 500cubic meters, and no permit is necessary. Any other use is commercial (ZINWA, 2002).
Lumbriso, (2003) also distinguished water use into three types, withdrawals or abstractions, consumptive use and non- consumptive use. Small dams exhibit all these in form of small holder irrigation, fish farming, brick making and domestic water purpose and other use. In light with this when carefully abstracted and exploited, the water in silt 9 of silted up small dams can go along way in improving rural livelihoods (WRMS undated). According to a study done in Mauritania, small dams have to reverse the rural exodus as seen by great number of people who lived nearby increasing annually (Chavula, 2000 ). Irrigation of small private gardens and community gardens is one other important benefit derived from using water stored up in the silt of silted up small dams especially during the dry spells and season that is when the dam is completely empty in (June – mid November). Socio-economic status of communities have improved as a result of selling of the produce through irrigation using water from silt wells. The nutritional status has also been improved due to the availability of vegetables and fruits through out the year (Ogbeide, et al 2003).
2.4. Environmental Aspects It is of importance to understand that water is essential in maintaining the function of ecosystems flora and fauna, which humans depend on direct and indirectly (Ellis Jones et al 1999). Rosegrant et al (2000) also pointed that the environment demands water for ecosystems sustenance and for regulating pollution. Soils loss due to erosion of crop lands in communal areas can be as high as 43 tones pe hectare per annual (WRMS undated). Most of the soil finds its way to small dams. H R Wallingford (2004) gives an estimate of the loss of storage in dams due to sedimentation ranging between 0.5% and 1% per annum. It has been found that annual siltation rates increases as the dam become small. This attributed to sediment delivery effects which usually results in increasing catchments sediment yields per square kilometre as the catchment area become smaller.