Tongxin Zhu

Runoff generation on a semi-arid agricultural catchment: field and experimental studies

Abstract Runoff generation on a small semi-arid agricultural catchment with mixed land use in the Loess Plateau of China was monitored over a 19-year period. To investigate the possible spatial variations in runoff generation on the catchment, eight plots were set up on various sections of the hillslope and monitored for 6 years. Only a small proportion of rainfall events generated runoff, contrary to the assumption that rainstorms in this area are characterized by high intensity and short duration, and thereby lead to runoff generation. Runoff occurrence and yields were also found to be highly variable within the catchment. To explore further the results obtained from the field observations, portable and downspraying sprinklers were used in field experiments. Both produce similar rainfall intensities but the raindrops from the portable sprinkler have very low kinetic energy and do not break down aggregates and form crusting, while raindrops produced by the downspraying sprinkler have similar characteristics to natural rainfall. A comparison of the experimental results obtained by those two kinds of sprinklers clearly demonstrated that runoff generation in this area is largely affected by surface crusting. The effects on runoff generation of the crusts formed during previous storms and the present storm were examined experimentally. Finally, the impacts of cultivation and plowing on runoff generation were determined through field investigation and experiments. This study suggests that there is considerable potential to reduce runoff and erosion, and to increase soil moisture and crop yields on the Loess Plateau through changes of currently inappropriate land use and the improvement of land management. ©1997 Elsevier Science B.V.

Deep-seated., complex tunnel systems — a hydrological study in a semi-arid catchment, Loess Plateau, China

Abstract During 1989–1990, delailed monitoring of deep-seated, complex tunnel systems was conducted in Yangdaogou, a subbasin in the Hilly Loess Region, Shanxi, which has a catchment area of 0.203 km2. It was found that tunnel flow hydrological processes were characterized by a quick response to rainfall, an early flow peak, and a short duration. All the tunnel discharge was derived from overland flow entering via inlets. However, discharge is not significantly related to rainfall parameters in some tunnels, which is contrary to observations on surface plots. Field surveys show frequent blockages of tunnels caused by collapses inside the tunnels which could be reopened in subsequent events, as well as the occasional abrupt opening of new inlets. As a result, tunnel discharge was highly erratic in some of the monitored events. Partial damming within the tunnel systems may also be involved. Hence, instability in the tunnel systems is one of the key factors affecting their hydrologic response. During the period of monitoring, fifteen events occurred and on average at least 43% (ranging from 0 to 78%) of the total basin water discharge was routed through four major tunnel systems which account for 90% of the catchment area of all tunnel systems in the basin. The deep-seated tunnel systems in this area seem not to be developed from the micro-pipes close to the surface. Instead, they are most likely formed in some catastrophic storms and expanded in subsequent storms. 1997 Elsevier Science B.V.

Tunnel erosion and sediment production in the hilly loess region, North China

In this study, detailed monitoring of water and sediment delivery from major tunnel systems was conducted in a small semi-arid sub-basin, locally known as Yangdaogou, in the hilly loess region, North China. These deep-seated tunnels are located as much as 30 m below the slope surface, in deep Quaternary loess formations. In the Yangdaogou, these systems have large amphitheatre-like inlets, with mean diameter and depth of 4.8 and 4.99 m, respectively. These dimensions represent some of the largest tunnel inlets in the world. During 1989 and 1990, fifteen rainstorms were monitored at six tunnel outlets. Due to practical difficulties, only 35 sets of tunnel-storm data were obtained. Observed sediment concentration of tunnel flows ranges from 8.2 to 893.2 g/l. The peak sediment concentrations in tunnel flows are not distinctively higher than those in channel flows but considerably higher than those measured from untunneled sideslopes. No significant correlations between runoff and sediment yield can be found in most tunnels at both within-and between-storm levels. Such an erratic relationship is ascribed to the rapid shift of runoff and sediment source area, the occurrence of collapses within tunnels, and the initiation of new tunnel inlets. Based on the field monitored data, 57% of basin sediment production is delivered by the tunnel systems, suggesting that tunnel erosion is a major erosion process in the hilly loess region.

A layered approach to parallel computing for spatially distributed hydrological modeling

Distributed hydrological simulations over large watersheds usually require an extensive amount of computation, which necessitates the use of parallel computing. Each type of hydrological model has its own computational characteristics and therefore needs a distinct parallel-computing strategy. In this paper, we focus on one type of hydrological model in which both overland flow routing and channel flow routing are performed sequentially from upstream simulation units to downstream simulation units (referred to as Fully Sequential Dependent Hydrological Models, or FSDHM). There has been little published work on parallel computing for this type of model. In this paper, a layered approach to parallel computing is proposed. This approach divides simulation units into layers according to flow direction. In each layer, there are no upstream or downstream relationships among simulation units. Thus, the calculations on simulation units in the same layer are independent and can be conducted in parallel. A grid-based FSDHM was parallelized with the Open Multi-Processing (OpenMP) library to illustrate the implementation of the proposed approach. Experiments on the performance of this parallel model were conducted on a computer with multi-core Central Processing Units (CPUs) using datasets of different resolutions (30?m, 90?m and 270?m, respectively). The results showed that the parallel performance was higher for simulations with large datasets than with small datasets and the maximum speedup ratio reached 12.49 under 24 threads for the 30?m dataset. A layered approach to parallel computing for distributed hydrological modeling.This approach divides simulation units into layers according to flow direction.In each layer, there are no upstream or downstream relationships among units.A grid-based model was parallelized to illustrate this approach.The speedup ratio reached 12.49 under 24 threads.

Experimental studies on the Danxia landscape morphogenesis in Mt. Danxiashan, South China

The formation of Danxia landscapes is too slow to be observed in our life time and the paleoclimates in which Danxia landscapes developed are significantly different from the present. Thus, this study adopted experimental approaches to examine the lithological and paleoclimatic control on the formation of various landscape morphologies in the Mt. Danxiashan, South China. A total of 122 rock samples were collected from a range of Danxia landscape morphologies such as white spots, small and large through caves, honeycomb caves, horizontal grooves, natural bridges, stone pillars, and squama stones. Analyses of the collected samples were conducted in different kinds of experiments, including uniaxial mechanical strength testing; rock resistance against sulfuric acid erosion, freezing, and thawing; X-ray fluorescence spectrometry (XRF) analysis; inductively coupled plasma mass spectrometry (ICP-MS) analysis; and identification analysis under a polarizing microscope. The results indicated that the formation of the various Danxia landscape morphologies could result from one or more of the following processes: differential erosion due to lithological difference, chemical dissolution and recrystallization, freezing and thawing actions, acid corrosion, weathering, lateral erosion of river flows, and tectonic uplifts. Water erosion in humid monsoon climate and the alternations of intensive freezing and thawing actions in the Quaternary glacial stages and the interglacial stages could have had great influences on the formation of Danxia landscape topographies.

Application of ArcGIS in Geography Teaching of Secondary School: A Case Study in the Practice of Map Teaching

With the development of modern geography, new requirements have been put forward for traditional geography teaching. Based on the implementation of secondary school geography teaching in China, and a case of application of ArcGIS in the practice of map teaching, the present work analyzes how to build the geographic information literacy and innovation ability of secondary school students by using the ArcGIS geographic information system software, and puts forward some recommendations, including (1) the compilation of ArcGIS teaching materials suitable for teachers and students’ characteristics; (2) the research and development of ArcGIS software for the secondary school education; and (3) the enhancement of ArcGIS training for secondary school geography teachers. It is hoped that the application of ArcGIS software can promote the development of geography teaching and provide modern teaching methods for secondary school geography. With the maturing of ArcGIS software it will become more popular among secondary school geography teachers, a development which will certainly take geography teaching in China’s secondary schools to a whole new level.