Seifu A. Tilahun

Citizen science in hydrology and water resources: opportunities for knowledge generation, ecosystem service management, and sustainable development

The participation of the general public in the research design, data collection and interpretation process together with scientists is often referred to as citizen science. While citizen science itself has existed since the start of scientific practice, developments in sensing technology, data processing and visualisation, and communication of ideas and results, are creating a wide range of new opportunities for public participation in scientific research. This paper reviews the state of citizen science in a hydrological context and explores the potential of citizen science to complement more traditional ways of scientific data collection and knowledge generation for hydrological sciences and water resources management. Although hydrological data collection often involves advanced technology, the advent of robust, cheap and low-maintenance sensing equipment provides unprecedented opportunities for data collection in a citizen science context. These data have a significant potential to create new hydrological knowledge, especially in relation to the characterisation of process heterogeneity, remote regions, and human impacts on the water cycle. However, the nature and quality of data collected in citizen science experiments is potentially very different from those of traditional monitoring networks. This poses challenges in terms of their processing, interpretation, and use, especially with regard to assimilation of traditional knowledge, the quantification of uncertainties, and their role in decision support. It also requires care in designing citizen science projects such that the generated data complement optimally other available knowledge. Lastly, we reflect on the challenges and opportunities in the integration of hydrologically-oriented citizen science in water resources management, the role of scientific knowledge in the decision-making process, and the potential contestation to established community institutions posed by co-generation of new knowledge.

Impact of conservation practices on runoff and soil loss in the sub-humid Ethiopian Highlands: The Debre Mawi watershed

Abstract In response to the continually increasing sediment concentrations in rivers and lakes, the Ethiopian government is leading an effort where farmers are installing soil and water conservation measures to increase infiltration and reduce erosion. This paper reports on findings from a four year study in the 95 ha Debre Mawi watershed where under the government led conservation works, mainly terraces with infiltration furrows were installed halfway in the period of observation. The results show that runoff volume decreased significantly after installation of the soil and water conservation practices but sediment concentration decreased only marginally. Sediment loads were reduced mainly because of the reduced runoff. Infiltration furrows were effective on the hillsides where rain water could infiltrate, but on the flat bottom lands that become saturated with the progress of the monsoon rain, infiltration was restricted and conservation practices became conduits for carrying excess rainfall. This caused the initiation of gullies in several occasions in the saturated bottomlands. Sediment concentration at the outlet barely decreased due to entrainment of loose soil from unstable banks of gullies in the periodically saturated bottom areas. Since most uphill drainage were already half filled up with sediments after two years, long term benefits of reducing runoff can only be sustained with continuous maintenance of uphill infiltration furrows.

Watershed Hydrology of the (Semi) Humid Ethiopian Highlands

Understanding the basic relationships between rainfall, runoff and soil loss is vital for effective management and utilization of water resources and soil conservation planning. A study was conducted in three small watersheds in or near the Blue Nile basin in Ethiopia, with long-term records of rainfall and discharge. To better understand the water movement within the watershed, piezometers were installed and infiltration rates were measured in the 2008 rainy season. We also reanalyzed the discharge from small plots within the watersheds. Infiltration rates were generally in excess of the rainfall rates. Based on this and plot discharge measurements, we concluded that most rainfall infiltrated into the soil, especially in the upper, steep and well-drained portions of the watershed. Direct runoff is generated either from saturated areas at the lower and less steep portions of the hill slopes or from areas of exposed bedrock. Using these principles, a simple distributed watershed hydrology model was developed. The models reproduce the daily discharge pattern reasonably well for the small watershed and the 10-day discharge values for the whole Blue Nile Basin in Ethiopia. The simplicity and scalability of the model hold promise for use in un-gauged catchments.

Spatial and Temporal Patterns of Soil Erosion in the Semi-humid Ethiopian Highlands: A Case Study of Debre Mawi Watershed

The effectiveness of water management interventions is hampered by the lack of knowledge about the spatial distribution of runoff and associated soil loss. A study was conducted in the 95-ha Debre Mawi watershed in the Upper Blue Nile basin to understand where and when runoff and erosion takes place on the landscape. During the rainy phase of the 2010 and 2011 monsoons, storm runoff and sediment concentrations were measured from five sub-watersheds. In addition, perched groundwater tables, infiltration rates, and rill erosion from agricultural fields were measured. The results show that saturation excess runoff was the main runoff mechanism because the median infiltration rate was only exceeded 3 % of the time. Early during the rainy period, runoff produced from upslope shallow soils infiltrated downslope and did not reach the outlet. At the end of July, the bottomlands became saturated, and the runoff coefficient at the outlet became greater than upslope areas. Sediment concentrations were greater in the beginning of the rainy monsoon phase when the rill network had developed on the plowed land and it becomes lowest at the end of rainy phase when rill formation stopped. At all times, the sediment concentration at the outlet was greater than upslope because both runoff losses were greater in the saturated bottomlands and loose unstructured soil was available from newly forming gullies. This research indicates that watershed management interventions to control erosion should be implemented in areas which produce the most runoff such as those shallow upland soils and bottomlands near the river that become saturated by the end of the rainy phase. In addition, for proper planning and management, runoff and erosion models should capture these dynamics.

Biohydrology of low flows in the humid Ethiopian highlands: The Gilgel Abay catchment

In Ethiopia the population is rapidly expanding. As a consequence the landscape is rapidly changing. Eucalyptus plantations are increasing and irrigation projects are implemented. The hydrological effects of the changing landscape on river (low) flows have not been well documented and therefore the amount of water available in the future might be over optimistic. The objective of this paper is to establish how low flows have been impacted by new developments in irrigation and by landscape change. For this paper, we choose the Gilgel Abay in the headwaters of the upper Blue Nile basin, since it has both good quality discharge data and it is located in the Tana Beles growth corridor. Numerical and statistical means were used to analyze the 25 years of available low flow data. We found a statistically significant decreasing trend (P < 0.00001) of low flow in the Gilgel Abay. From 1980’s to 1990’s the low flow decreased by 25% and from 1990’s to 2000’s the low flow was reduced by 46%. The deterministic analysis with the Parameter Efficient Distributed (PED) model supported the statistical findings and indicated that in the middle of the nineteen nineties, after irrigation projects and eucalyptus plantations increased greatly, the low flows decreased more rapidly.

Modeling sediment concentration and discharge variations in a small Ethiopian watershed with contributions from an unpaved road

Abstract Drainage of paved and unpaved roads has been implicated as a major contributor of overland flow and erosion in mountainous landscapes. Despite this, few watershed models include or have tested for the effect roads have on discharge and sediment loads. Though having a model is an important step, its proper application and attention to distinct landscape features is even more important. This study focuses on developing a module for drainage from a road and tests it on a nested watershed (Shanko Bahir) within a larger previously studied site (Debre Mawi) that receives overland flow contributions from a highly compacted layer of soil on an unpaved road surface. Shanko Bahir experiences a sub-humid monsoonal climate and was assessed for the rainy seasons of 2010, 2011, and 2012. The model chosen is the Parameter Efficient Distributed (PED) model, previously used where saturation-excess overland flow heavily influences discharge and sediment concentration variation, though infiltration-excess occasionally occurs. Since overland flow on unpaved surfaces emulates Hortonian flow, an adjustment to the PED model (the developed module) advances possible incorporation of both flow regimes. The modification resulted in similar modeling performance as previous studies in the Blue Nile Basin on a daily basis (NSE = 0.67 for discharge and 0.71 for sediment concentrations). Furthermore, the road while occupying a small proportion of the sub-watershed (11%) contributed importantly to the early discharge and sediment transport events demonstrating the effect of roads especially on sediment concentrations. Considerations for the dynamic erodibility of the road improved sediment concentration simulation further (NSE = 0.75). The results show that this PED modeling framework can be adjusted to include unpaved compacted surfaces to give reasonable results, but more work is needed to account for contributions from gullies, which can cause high influxes of sediment.

Modeling discharge and sediment concentrations after landscape interventions in a humid monsoon climate: the Anjeni watershed in the highlands of Ethiopia

Increasing population and intensification of agriculture increase erosion rates and often result in severe land degradation and sedimentation of reservoirs. Finding effective management practices to counteract the increasing sediment load is becoming increasingly urgent especially in the Ethiopian highlands where the construction of the hydroelectric Grand Renaissance Dam on the Blue Nile is underway. In this paper, we examine the results of nine years of a watershed experiment in which discharge and sediment losses were observed in the 113 ha Anjeni watershed of the Blue Nile Basin. The study period encompasses conditions before, during, and after the installation of graded Fanya-Juu (“throw uphill” bunds) soil and water conservation practices (SWCP) which had the ultimate goal of creating terraces. We use a saturation-excess runoff model named the Parameter Efficient Distributed (PED) model as a mathematical construct to relate rainfall with discharge and sediment losses at the outlet. The PED model is based on landscape units in which the excess rainfall becomes direct runoff or infiltrates based on topographic position or hardpan characteristics. Deviations in this rainfall-discharge-sediment loss relationship are ascribed to the changes in infiltration characteristics caused by SWCPs on the hillslopes. With this technique we found that in the Anjeni basin the Fanya-Juu SWCPs are only effective in increasing the infiltration and thereby reducing the direct runoff and sediment concentrations in the first 5 years. At the end of the 9 year observation period the direct runoff and sediment concentrations were barely reduced compared to the levels before SWCP were installed. In addition, we found that the model structure based on landscape units was able to represent the varying runoff and erosion processes during the nine years well by varying mainly the portion of degraded land (and thereby representing the effectiveness of the Fanya-Juus to reduce runoff by increasing infiltration).

Soil Erosion and Discharge in the Blue Nile Basin: Trends and Challenges

Future river discharge predictions seldom take into account the degrading landscape. The objective of this study was to investigate the relationship of river discharge and sediment concentrations, and the effect of changing landscape and climate on discharge and sediment transport in the Ethiopian Blue Nile basin. This study used past precipitation records and the Parameter Efficient Distributed (PED) model to examine how the relationship between precipitation, discharge, and sediment concentration changed with time. All input data to the PED model were kept constant except for a conversion of permeable hillside to degraded soil in time. The results of this study show that with a gradual increase of the degraded areas from 10 % in the 1960s to 22 % in 2000s, the observed discharge pattern and sediment concentration can be simulated well. Simulated annual runoff increased by 10 % over the 40-year periods as a result of the increase in degraded soils. Sediment loads appeared to have increased many times more, but this needs to be further validated as data availability is limited. In general, the results indicate that rehabilitating the degraded and bare areas by planting permanent vegetation can be effective in decreasing the sediment concentration in the rivers. Research should be undertaken to evaluate the effectiveness of vegetation planting.

Improving watershed management practices in humid regions

In many parts of the world, watershed management practices have been extremely effective. However, implementation of soil and water conservation technologies in the humid African highlands, while beneficial in the short term, were remarkably unsuccessful in the long term. Insights from community knowledge perspectives have revealed that alternative methods are needed. Although conservation practices are designed to conserve water in semi-arid areas, safely draining excess water is needed in humid areas. The objective of this paper is to review current watershed management approaches used in humid regions as exemplified by those used in Ethiopian highlands and then based on these findings propose more effective practices. Although current government sponsored practices primarily protect the hillsides, direct run-off is generated from areas that become saturated on valley bottoms near rivers and on specific parts of the hillsides with degraded soils (or with highly permeable surface soils) and with perched water tables on slowly permeable horizons at shallow depths. In these areas, direct run-off is increasing with deforestation and the soil degradation, demanding additional drainage ways that evolve in the form of gullies. Therefore, watershed management interventions for erosion control should prioritize revegetation of degraded areas, increasing sustainable infiltration, and rehabilitating gullies situated at saturated bottomlands.

Root reinforcement to soils provided by common Ethiopian highland plants for gully erosion control

Biological and Environmental Engineering, Cornell University, Ithaca, NY, USA Amhara Region Agricultural Research Institute, Bahir Dar, Ethiopia U.S. Department of Agriculture, Agricultural Research Service, National Sedimentation Laboratory, Oxford, MS 38655, USA Faculty of Civil and Water Resources Engineering, Bahir Dar University, Bahir Dar, Ethiopia 5 International Water Management Institute (IWMI), P. O. Box 5689, Addis Ababa, Ethiopia Department of Earth and Environmental Sciences, KU Leuven, Celestijnenlaan 200E, Leuven 3001, Belgium Correspondence Eddy J. Langendoen, U.S. Department of Agriculture, Agricultural Research Service, National Sedimentation Laboratory, Oxford, MS 38655, USA. Email: eddy.langendoen@ars.usda.gov