Experimental determination of the flood wave transformation and the sediment resuspension in a small regulated stream in an agricultural catchment

Abstract

Abstract. This paper presents the methodology used for artificial flood experiments conducted in a small artificial, trained (regulated) channel on the Nučice experimental agricultural catchment (0.5 km 2 ), central Czech Republic, and the results of the experiments. The aim was to monitor the transformation of the flood wave and the sediment transport within the channel. Two series of experiments were carried out in contrasting initial conditions: (a) in September, when the stream banks were dry, the baseflow was negligible, and the channel was fully overgrown with vegetation; and (b) in March, when the stream banks were almost water saturated, the baseflow was above the annual average, and there was no vegetation present. Within each campaign, three successive flood waves, each with an approximate volume of 17 m 3 and peak flow of ca. 40 L s −1 , were pumped into the upper part of the catchment drainage channel. The transformation of the flood wave and the sediment transport regime within an approximately 400 m long channel section were monitored by measuring the discharge, the turbidity, and the electrical conductivity in three profiles along the stream. On the basis of the results, it was concluded that there is a considerable amount of deposited sediment, even in the well-trained and straight channel that can be re-mobilized by small floods. Part of the recorded sediment therefore originates from the particles deposited during previous soil erosion events. The flood waves initiated in dissimilar instream conditions progressed differently -we show that the saturation of the channel banks, the stream vegetation and the actual baseflow had a strong influence on the flood transformation and the sediment regime in the channel. The sediment moves quickly in winter and early spring, but in the later part of the year the channel serves as a sediment trap and the resuspension is slower, if dense vegetation is present.

An overview of hydrometeorological datasets from a small agricultural catchment (Nučice) in the Czech Republic

“…Discharge is monitored at two locations in the stream. Firstly, in the culvert below the upper field; a pressure probe is installed for water depth monitoring and the discharge is calculated based on the circular culvert free-flow discharge relationships, which has been recalibrated during flood wave experiments in 2013, 2014, and 2020 (Zumr et al, 2017) has the best accuracy at their respective discharge ranges. The water level is measured by pressure transducers (LMP307, BD Sensors, Czech Republic, accuracy = ±0.1%) and a sonic distance sensor (SR50A, Campbell Sci., UK, accuracy = ±10 mm) in the flume with Htype facing.…”

“…Even though the channel F I G U R E 1 Overview of the Nučice catchment: (a) catchment location, (b) catchment overview, (c) view from the lower part of the catchment, and (d) view from the upper part of the catchment is straight and short, it has a high retention capacity and the flood wave peaks during runoff events are attenuated. The channel serves as a trap for eroded sediment during the summer months due to dense instream vegetation (Zumr et al, 2017). (Table A1).…”

“…Discharge is monitored at two locations in the stream. Firstly, in the culvert below the upper field; a pressure probe is installed for water depth monitoring and the discharge is calculated based on the circular culvert free-flow discharge relationships, which has been recalibrated during flood wave experiments in 2013, 2014, and 2020 (Zumr et al, 2017) For the hydrological data, the stream discharge in the dataset includes the measured discharge at the catchment outlet since the end of 2013. Quality control of the runoff data (removal of extreme values caused by measurement errors) was implemented, and the runoff was saved at a 10-min time resolution.…”

Impact of stacked conservation practices on phosphorus and sediment export at the catchment scale

“…Furthermore, a small catchment study requires a shorter treatment response time (i.e., lag time) to show water quality improvements; subsequently, a shorter study period and lower monitoring costs are needed when compared to a larger watershed (Dressing & Meals, 2005;Meals & Dressing, 2008). At the catchment scale, the immediate impact of precipitation patterns (dry vs. wet period) on P and sediment delivery can be evaluated, with the advantage of less complexity resulting from in-stream processes typically observed at larger streams or rivers (Meals & Dressing, 2008;Zumr et al, 2017). Although the study of streambed sediments is beyond the scope of this project, they are an important source for downstream P and sediment delivery.…”

Estimates of Tillage and Rainfall Effects on Unsaturated Hydraulic Conductivity in a Small Central European Agricultural Catchment

“…There are no forests, grasslands or urbanized areas. The Nučice catchment is drained by a narrow stream, which has been piped in the uppermost part [37]. The average altitude is 401 m a.s.l., the mean land slope is 3.9%, and the climate is humid continental.…”