Erik van den Elsen

A new wireless underground network system for continuous monitoring of soil water contents

A new stand-alone wireless embedded network system has been developed recently for continuous monitoring of soil water contents at multiple depths. This paper presents information on the technical aspects of the system, including the applied sensor technology, the wireless communication protocols, the gateway station for data collection, and data transfer to an end user Web page for disseminating results to targeted audiences. Results from the first test of the network system are presented and discussed, including lessons learned so far and actions to be undertaken in the near future to improve and enhance the operability of this innovative measurement approach.

Discharge and sediment measurements at the outlet of a watershed on the Loess plateau of China

A dam and weir system was constructed to measure the discharge of water and sediment from a selected small catchment on the Loess plateau in China. The aim of the system described here was to collect data on discharge and sediment content during occasional summer storms. These data can be used for calibrating and validating the LISEM erosion model. A V-notch weir was selected since it can measure a wide range of discharges. The measurement structure was equipped with an ultrasonic sensor to measure the water level. The system automatically switched on as soon as rain had been detected and the water level data were stored when a certain level threshold was surpassed. As a back-up system a flow meter was used, while a local farmer had also been hired to manually record water level during events. Sediment content of the runoff was determined on samples taken by an automatic sampler and a local farmer took additional samples. The system operated from April 1998 until September 2000. In this period, six events occurred and data could be collected during five of those. The data were corrected to make them useful for comparison with erosion simulation results. The collected data show that runoff only occurs during high-intensity rainstorms that produce more than about 11 mm of rain.

Intensive water content and discharge measurement system in a hillslope gully in China

Abstract An automatic monitoring system was constructed to intensively study the water–profile–runoff interactions during rain events, of a hillslope gully. The system was installed on the Loess plateau in the Shaanxi province in northern China. The primary goal was to obtain a better understanding of soil erosion processes in this district to aid in better management. To accomplish this, infiltration and runoff data for running, calibrating and validating the LISEM erosion model was needed. The system presented here consisted of 29 Time Domain Reflectometry (TDR) water content sensors that monitored the water content variation in time. Sensors were installed in different subsystems throughout the gully geometry such as in the cropland surrounding the gully, in some gully slopes and in the gully floor. At the outflow point of the gully, an H-flume was installed in order to measure the actual discharge of the gully system and to measure directly the sediment concentration in the discharge. The monitoring system was programmed in this way so that more measurements were recorded when a rainstorm occurred. Installation took place in April 1998 and it was used until September 2000. In 1998, five major rain events were recorded, which generated runoff and erosion, in 1999 and 2000 only one. Cropland measurements showed high water contents and high infiltration rates all through the measuring period and also showed a strong reaction to precipitation. The sidewalls of the gully showed much lower water contents where only very shallow parts showed some infiltration during rain showers, while steep parts of the gully, such as pipes and vertical walls, showed an extremely low water content and practically no water content variation with time. Simulation results confirmed the suspicion that these areas are an important source for Hortanian overland flow within the gully system. Model simulations further showed that most of the sediment being eroded from the gully system was coming from rills and smaller gullies being cut into the main gully bottom. Saturation excess overland flow proved to be dependent on the characteristic of the rain event as well as on the water content of the soil at the beginning of the event.

MEASURING AND MODELLING OF SOIL WATER DYNAMICS AND RUNOFF GENERATION IN AN AGRICULTURAL LOESSIAL HILLSLOPE

Surface run-off may be generated when rainfall intensity exceeds infiltration capacity, or when the soil profile is saturated. Both types of overland flow may occur in hilly agricultural loess regions. It was shown with pressure head and run-off measurements that Hortonian overland flow occurs during summer rain events. A two-dimensional water flow model could simulate pressure head changes and run-off. Simulated potential run-off for the transect studied was three times as high. This indicates effects of surface ponding and the probable location of this particular transect in a region with high run-off production.

Animating measured precipitation and soil moisture data

Nowadays more and more measurement sites are installed in the field to gain insight in the process of 2-dimensional moisture flow in topsoils in dependence of the weather conditions. As these measurements yield a large amount of data, visualization is essential and therefore a software package was developed consisting of several tools to process the measured data by creating animated movies of the changes in soil moisture content in time. This paper presents the software, the dataflow between the tools, a description of the tools and some examples of input and output.