High resolution rainfall – runoff measurement setup for green roof experiments in a tropical environment

T. Vergroesen, U. Man Joshi, N. C. van de Giesen, F. H. M. van de Ven
2010 Hydrology and Earth System Sciences Discussions  
This article describes the measurement setup that is used for green roof experiments in a tropical environment, the required data treatment to obtain reliable values of rainfall, runoff and evapotranspiration, and how to deal with external disturbances that can influence the experiment results. High resolution rainfall runoff measurements to identify, 5 understand and properly model the relevant runoff processes in a green roof require both tailored equipment and data treatment. A tipping
more » ... nt. A tipping bucket rain gauge is calibrated for and installed to measure minute based rain intensities. A runoff measuring setup is developed that can accurately quantify the runoff up to 6 l/min, and has a high resolution in both time and volume. Two different measuring setups are used to verify the 10 evapotranspiration that is derived from the rainfall and runoff measurements. 20 Most practical way to measure the runoff is to use self emptying contraptions like tipping buckets, and record the number of tips per time interval like it is done in tipping bucket rain gauges. Rainfall in Singapore can generate runoff up to 3 l/min from our experiment roofs on a regular base. Using a rain gauge tipping bucket (±10 ml/tip) to measure this runoff can result in a tipping frequency up to 5 tips/s. That is way 25 beyond its accuracy. So measuring flows like that requires much larger tipping buckets. 9368 HESSD Disadvantage of large tipping buckets however is that runoff from low intensive rainfall can not be monitored accurately. In this paper we elaborate on the measuring method we apply to obtain accurate high resolution runoff data for the entire Singapore rainfall spectrum. -We explain precisely how we measure both rainfall and runoff accurately with 5 a high resolution (Sect. 2). For measuring rainfall we only use a smaller time interval than normally is done, and we have calibrated the rain gauge before using it. We have developed the runoff measuring method ourselves. -We prove that our measuring method is sound, and explain how the raw data have to be treated to generate the required output (Sect. 3). 10 -We explain how to deal with external influences that can disturb the measurements (Sect. 4). The range of possible external influences is always wider than you can imagine when you start an experiment. -We compare our way of measuring to methods that were used elsewhere, and discuss the pros and cons (Sect. 5). 15 -Finally we summarize the main conclusions, and give some recommendations to further improve this method (Sect. 6). The measurements are divided into rainfall measurements and runoff measurements. In addition we use weather parameters like air pressure and temperature, wind speed and direction, humidity and incoming radiation to determine the evaporation. 20 These data are recorded at a 5 min time interval by a weather station of the National University of Singapore that is located at approximately 100 m from our experiment site. The NUS weather station also records rainfall at a 5 min time interval. During the testing phase of the experiments we used the rainfall data from the NUS weather station as well, and compared them to the measured runoff. Several times during the testing 25 phase the measured runoff did not correspond well with the measured rainfall. The 9369 HESSD Abstract 20 The rain gauge is adjusted to record the number of tips per minute (NRT). The calibration of the rain gauge tipping bucket (Sect. 3), resulted in the following conversion rule: Rainfall (mm/min) = NRT · (0.2049 + 0.0019 · NRT) 9370 HESSD
doi:10.5194/hessd-7-9367-2010 fatcat:72uiahajxnhadogbafs3zfncqe