Monitoring of Watershed Processes in Southeast Burkina Faso for Improvement of Local Hydrologic Models, Ecohydrologic Analysis and Sustainable Resource Use

As in all semi arid regions, the activities of Tambarga, a small village surrounded by national parks in the landlocked country of Burkina Faso, are subject to the seasonality of the local hydrology. Seasonal and spatial variability of rainfall shapes the livelihood of rural farmers, which consists mainly of rain-fed agriculture. We instrumented the Tambarga catchment (area=3.4 km2) to study the hydrologic processes including surface runoff formation, base flow, evaporation, and land cover controls on the local water balance. Thus, we have measured hydrological, meteorological and soil parameters at high spatial and temporal resolution over the catchment since 2009. Data for this research were acquired during mainly the 2010 rainy season using an array of wireless weather stations (SensorScope) as well as two weirs, six piezometric wells, and surface energy balance stations that use eddy correlation to calculate heat flux measurements. 

This research takes place on the border between agricultural parkland and Sudanian shrubby savanna in the commune of Madjoari, southeastern Burkina Faso. We are working with communities and institutions on site to transfer these findings into local practices, using a participatory approach. We integrate our study of the biophysical system with understanding of socio-agricultural pressures in the setting of a geographically and economically isolated village. Up until now we have contributed to a communal reforestation effort centered around a newly created botanical garden, and an environmental resource-information center that serves as a forum for local actions and activities.  In the future we hope to use these efforts as a pathway to deliver the results of the research to the village in the form of concrete recommendations, variables, and actions. 

Natalie uses the network of wireless sensors to asses the hydrologic importance of vegetation in the Sudanian savanna, both at the scale of an individual Sclerocarya birrea agroforestry tree and that of the small catchment.  Vegetation connects groundwater with soil moisture and atmospheric humidity and permits absorption of precipitation by the surface soil, vegetation, and deep groundwater. It may buffer the severity of droughts by absorbing water from the rainy season and facilitating access to groundwater resources during the dry season. In addition to the small portable wireless sensor network of meteorological stations, she also uses sap flow sensors, eddy covariance equipment, isotope analysis and various manual measurements.  Currently she is working on a distributed energy balance of the watershed, but she has also completed a soil moisture balance around a tree, examined soil hydraulic properties, begun an isotope analysis of stem water used by the tree, and started putting her hydrologic analysis into a social context.  Together, this research improves understanding of the hydrologic consequences of land conversion, which is essential for developing land use practices that conserve ecosystem function.

Theophile's research concerns the watershed hydrological modeling. He focuses on an analysis of the runoff dynamics that link the correlation between the surface runoff and base flow with the land use. The hydrologic processes were identified over the basin and intermittent responses of stream flow were isolated over the course of the 2010 season. The rise of the perched water tables located in the upstream and downstream of basin generated two separate flows in the riverbed after the first rain. The intermediate zone operates like a deep storage tank, and by filling, it allows a connection between the two perched water tables that induces a continuous flow throughout the 1.5 km of the stream. The hydrologic response at the basin outlet is observed to alternate between three different states over the course of the season. At the start of the rainy season, when the soils are very dry with a low groundwater level, a typical single-peak hydrograph is observed. This evolves into a double-peak and eventually a triple-peak hydrograph when the rainy season is completely established. Given the importance of rainfall-runoff processes in this catchment, a water balance was completed to understand the soil moisture feedback and groundwater recharge. The water balance highlights the importance of precipitation distributed between convective rainfalls and non-convective and characterized by their high intensity and short duration.  The understanding of hydrologic process in the Tambarga basin and the time series of relevant data collected allowed the development of a hydrologic model whose results are promising. Several scenarios will be tested with this model and strategies based on a rational exploitation of water resource will be proposed at local peoples for a better agricultural production and environmental protection.

 

Addresses

PRCCU : Projet de Renforcement des Capacités des Communes Urbaines
Ingénieur Civil. Seydou Kabore,
E-mail : seydou.kabore@fasonet.bf
11 BP 1488 CMS Ouagadougou 11, Burkina Faso,
http://www.prccu.bf Tel: +226 50 30 28 83/86

Environmental Fluid Mechanics (ENAC - EFLUM), http://eflum.epfl.ch/
Professeur Marc Parlange, Tel: +41 21 693 6391 Fax: +41 21 693 6390
EPFL - ENAC - EFLUM
Bâtiment GR, Station 2
CH-1015 Lausanne
Switzerland

Cooperation à EPFL: Professeur Jean-Claude Bolay, PhD et Repetti
Alexandre
Tel: +41 21 693 6012, Fax: +41 21 693 6010 http://cooperation.epfl.ch
CM 2 - Station 10
CH-1015 lausanne
Tel +41 21 693 36 12

Laboratoire Communication Audio-Visuel (LCAV)
Professeur Martin Vetterli, Tel: +41 21 693 5698/ 5634, http://lcavwww.epfl.ch
EPFL-I&C-LCAV
Station 14
CH-1015 Lausanne
SWITZERLAND

Dr. Hamma Yacouba,
E-mail: Hamma.yacouba@2ie-edu.org
Tel: +226 50 30 20 53
Fax: +226 50 31 27 24
Rue de la Science
01 BP 594
Ouagadougou 01
BURKINA FASO
Site Web : www.2ie-edu.org

Theophile Mande & Natalie Ceperley
EPFL - ENAC - EFLUM
Bâtiment GR, Station 2
CH-1015 Lausanne
Switzerland
natalie.ceperley@epfl.ch
theophile.mande@epfl.ch

The hill of Tambarga behind the village of the same name, the most prominent feature in our watershed

Crossing of scientists, officials, and delegates across the Singou River to the participatory workshop