Variation Trend Analysis of Runoff and Sediment Time Series Based on the R/S Analysis of Simulated Loess Tilled Slopes in the Loess Plateau, China

Ju Zhang,Qingwu Hu,Shaohua Wang,Mingyao Ai

doi:10.3390/su10010032

Abstract

The objective of this study was to illustrate the temporal variation of runoff and sediment of loess tilled slopes under successive rainfall conditions. Loess tilled slopes with four microtopography types (straight cultivated slope, artificial backhoe, artificial digging, and contour tillage) under five slope gradients (5°, 10°, 15°, 20°, 25°) were simulated and a rainfall intensity of 60 mm/h was adopted. The temporal trends of runoff and sediment yield were predicted based on the Rescaled Range (R/S) analysis method. The results indicate that the Hurst indices of runoff time series and sediment time series are higher than 0.5, and a long-term positive correlation exists between the future and the past. This means that runoff and sediment of loess tilled slopes in the future will have the same trends as in the past. The results obtained by the classical R/S analysis method were the same as those of the modified R/S analysis method. The rationality and reliability of the R/S analysis method were further identified and the method can be used for predicting the trend of runoff and sediment yield. The correlation between the microtopography and the Hurst indices of the runoff and sediment yield time series, as well as between the slopes and the Hurst indices, were tested, and the result was that there was no significant correlation between them. The microtopography and slopes cannot affect the correlation and continuity of runoff and sediment yield time series. This study provides an effective method for predicting variations in the trends of runoff and sediment yield on loess tilled slopes.

Highlights

The Loess Plateau is located in the northern part of China, covering the north of the Qinling Mt, south of the Yinshan Mt, west of the Taihang Mt, and east of the eastern edge of the Qinghai–Tibet Plateau (34◦45 –39◦40 N, 107◦28 –111◦15 E), with a total area of 62.68 × 104 km2.Loess tableland, ridge, and hillock topographies are the basic topographical types of the Loess Plateau
The results showed that microtopography and slope are not influencing factors on the long-term correlations of runoff and sediment yield
The characteristics of runoff and sediment yield under different microtopographies on the Loess Plateau are studied, and the trend of water and sediment time series were analysed by the R/S analysis method

Summary

Introduction

The Loess Plateau is located in the northern part of China, covering the north of the Qinling Mt, south of the Yinshan Mt, west of the Taihang Mt, and east of the eastern edge of the Qinghai–Tibet Plateau (34◦45 –39◦40 N, 107◦28 –111◦15 E), with a total area of 62.68 × 104 km.Loess tableland, ridge, and hillock topographies are the basic topographical types of the Loess Plateau. The terrain is high in the northwest and low in the southeast. The terrain can be divided into high-mountain area (800–3000 m elevation), middle-mountain area (600–800 m elevation), and low-mountain area (400–600 m elevation) [1]. The total area of the land with slopes of more than 15 degrees is nearly 50%. Loess is the most widely distributed and the most developed quaternary sediment in the Loess Plateau, accumulation of which began about 240 million years ago and has extended to modern times. Affected by factors such as climate and altitude, the soil types in the Loess Plateau have obvious zonation patterns. Soil nutrients and water content are generally low and the soil is loose

Objectives

Methods

Results

Discussion

Conclusion