Effects of topography and land use change on gully development in typical Mollisol region of Northeast China

Abstract

Due to high intensity agricultural exploitation since the middle of the 20th century, farmland gullies have become a pervasive form of water erosion in Northeast China. Yet few researches are concentrated on how topography and land use affect long-term gully development in this region. In this study, gully distribution in a village with an area of 24.2 km 2 in the central Mollisols area of Northeast China in different times were compared by Aerial photography (1968), Quickbird image (2009) and field survey, and factors affecting gully development including land use and topography were analyzed. The results showed that the total gully number decreased from 104 to 69, while occupying area rose from 34.8 ha to 78.4 ha from 1968 to 2009. Fundamental gully distribution had been formed by 1968 as most of 2009′s gullies were evolved from 1968′s gullies′ merge and width expansion process, and new gullies those initiated after 1968 occupied only 7% of total gully area in 2009. Gully area increasing ratio in grassland was the highest and that in forestland was the lowest. The threshold catchment area between simple and complex gully development was around 15 ha to 25 ha. This threshold value sets apart catchment areas that will develop simple or complex gullies in areas with similar environmental conditions. Gully control measurements were urgent because if appropriate gully control implements would not be applied, present gully erosion crisis could be doubled within 50 years.

Spatial-temporal changes in flow hydraulic characteristics and soil loss during gully headcut erosion

“…This phenomenon was agreed with previous studies (e.g. Su et al, 2015;Zhang et al, 2016;Shi et al, 2020a). Besides, for the same upstream inflow discharge, the Re and Fr of UA were larger than that of GB by 50.5%-65.9% and 1.39-2.04 times, respectively, indicating that the runoff https://doi.org/10.5194/hess-2020-412 Preprint.…”

“…5c, 5e), which was mainly attributed to the shortening of jet-flow height caused by the development of second headcut and upstream flow undercutting headcut brink-point (Guo et al, 2019). This result, however, differed from the finding of Zhang et al (2016) who stated the Ve and j remained stable as the experiments progressed, which was mainly attributed to the weak change of jet-flow height induced by slow headcut retreat.…”

“…5a), which was closely corresponded to the gradually decreased runoff width on the upstream area with time (Shi et al, 2020a). However, this result was inconsistent with Zhang et al (2016Zhang et al ( , 2018 and Shi et al (2020b) who reported that the Vb decreased over time, which was mainly due to the gradually increased roughness and resistance of underlying surface over time reducing the runoff velocity (Su et al, 2015). The further analysis of power function between Vb and time (Vb=a•t b , Table 1) showed that the a-value increased but the b-value showed a weak variation with the inflow discharge increased, indicating that upstream flow can improve initial Vb but not affect its change trend over time.…”

“…Based on the measured runoff velocity (VJ, m s -1 ) before runoff arrived at the headcut brinkpoint, the runoff depth (db, m) at the headcut brinkpoint, the plunge pool depth (DH, m) and the vertical distance (h, m) ( Fig. 4a), the three parameters including the runoff velocity at the headcut brinkpoint (Vb), jet-flow velocity entry to plunge pool (Ve) and jet-flow shear stress (  j) were calculated to clarify the change of jet properties (Rouse, 1950;Hager, 1983;Stein et al, 1993;Flores-Cervantes et al, 2006;Zhang et al, 2016). The three parameters were calculated as follows.…”

The effectiveness of selected vegetation communities in regulating runoff and soil loss from regraded gully banks in the Mollisol region of Northeast China

“…As a grain production base, 20% of the production is supplied from this region and feeds most of the population of China (Xie et al, 2019); however, the annual reduction of grain production due to gully erosion is as high as 36.2 × 10 5 tons (Liu, Li, Zhang, Cruse, & Zhang, 2019). Despite these worrying values, much less attention has been paid to gully protection than to gully erosion monitoring and erosion prediction, and there is a dire lack of research on gully bank protection (Bai & Hui, 2015; Li, Cruse, Liu, & Zhang, 2016; Yang et al, 2017). The gully bank, as the main landform unit of the gully, is characterized by a steep slope and high soil erodibility.…”