Using a Smart-phone for Collecting Discharge Data in Irrigation Furrows in Tanzania.

Abstract:

When managed effectively and sustainably crop yield in irrigated agriculture can be up to three times than in rainfed agriculture. Unsurprisingly, irrigation agriculture is globally gaining in importance. This is especially true in Africa where the share of irrigated to rainfed agriculture in terms of area cultivated is below global averages.

A large-scale expansion of irrigation, nonetheless has the potential to alter the natural hydrological cycle at local up to basin scales. In all cases, a good understanding of the water balance is needed. However, and especially in the developing context, data are scarce and knowledge about the available resources is most often not present. Some of the key reasons are: a) traditional monitoring approaches do not scale in terms of costs, b) repair is difficult and c) vandalism. There is a clear need of cheaper and easy-to-use methods for gathering information on water use and water availability.

We have developed a mobile device application for measuring discharge in rivers and irrigation furrows. The discharge is computed by analysing a few seconds of a movie recorded using the built-in camera. The great advantage is that the only requirement is that the field of view contains two reference markers with known scale and with known position relative to the channel geometry, a priori knowledge on the channel geometry and its roughness. The other great advantage is that the data collected (water level, surface velocity and discharge) can be sent via SMS or web-service to a central database.

The app is being currently used in a formerly ungauged catchment, the Themi River, which is part of the Pangani Basin in Tanzania. Furrow leaders and community members measure furrow discharges on-farm and monitor water levels in rivers off-farm. These community members were given a smartphone and received thorough training. Additionally, off-grid members have received a mobile recharging solution. Operational Expenses of the community members who are performing crowd-sensing are fully compensated via a clear contractual relationship with a Service Center. Since the beginning of 2015, data are collected at 11 river sites and 23 furrow intakes on a daily basis. Average instrumentation costs per river/furrow site are in the order of USD 200.-. Average monthly operational costs are USD 15.- per site.