6.4 Results and Discussion . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 79
6.4.1 Analysis of the Catastrophic Loess Landslides . . . . . . . 79
6.4.2 Soil Erosion Caused by Loess Landslides . . . . . . . . . . 87
6.4.3 Urgent Desires and Effective Measures to Prevent
Landslides . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 90
6.5 Conclusions . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 91
References . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 91
7 Effects of Conservation Practices on Soil, Water,
and Nutrients . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 95
7.1 Effects of Soil Conservation Practices . . . . . . . . . . . . . . . . . . . 95
7.2 Characteristics of the Nanxiaohegou Catchment . . . . . . . . . . . . 97
7.3 Methods and Materials . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 97
7.4 Results and Discussion . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 101
7.4.1 Distributions of Water, Soil, Nutrients, and Total
Retention Efficiency . . . . . . . . . . . . . . . . . . . . . . . . . . 101
7.4.2 Retention Ability and Retention Ratio . . . . . . . . . . . . . 101
7.4.3 Positive Effects of the Conservation Practices . . . . . . . 105
7.4.4 Negative Effects of the Conservation Practices . . . . . . . 106
7.4.5 Role of Check Dam in Reducing Soil
and Water Loss . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 107
7.4.6 Future Research Scenarios . . . . . . . . . . . . . . . . . . . . . 108
7.5 Conclusions . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 109
References . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 109
8 Sediment-Storage Effects of Check-Dam System in the Small
Watershed . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 113
8.1 Relative Stability and Optimum Programming
of Check Dams on the Loess Plateau . . . . . . . . . . . . . . . . . . . . 113
8.2 Characteristics of the Yangdaogou Catchment . . . . . . . . . . . . . 117
8.3 Experimental Methods . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 118
8.3.1 Runoff Simulation . . . . . . . . . . . . . . . . . . . . . . . . . . . 119
8.3.2 Rainfall Simulation . . . . . . . . . . . . . . . . . . . . . . . . . . . 122
8.4 Results and Discussion . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 125
8.4.1 Mechanism of the Relative Stability Development . . . . 127
8.4.2 Further Research on the Theory of Relative
Stability . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 130
8.4.3 Comparison of Sediment Loss and Dam-Land
Area . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 132
8.4.4 Comparison of the Water Discharge and Sediment
Concentration . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 134
8.4.5 Relationship Between the Dam-Land Increase
and Erosion Reduction . . . . . . . . . . . . . . . . . . . . . . . . 136
Contents
xix
6.4.1 Analysis of the Catastrophic Loess Landslides . . . . . . . 79
6.4.2 Soil Erosion Caused by Loess Landslides . . . . . . . . . . 87
6.4.3 Urgent Desires and Effective Measures to Prevent
Landslides . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 90
6.5 Conclusions . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 91
References . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 91
7 Effects of Conservation Practices on Soil, Water,
and Nutrients . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 95
7.1 Effects of Soil Conservation Practices . . . . . . . . . . . . . . . . . . . 95
7.2 Characteristics of the Nanxiaohegou Catchment . . . . . . . . . . . . 97
7.3 Methods and Materials . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 97
7.4 Results and Discussion . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 101
7.4.1 Distributions of Water, Soil, Nutrients, and Total
Retention Efficiency . . . . . . . . . . . . . . . . . . . . . . . . . . 101
7.4.2 Retention Ability and Retention Ratio . . . . . . . . . . . . . 101
7.4.3 Positive Effects of the Conservation Practices . . . . . . . 105
7.4.4 Negative Effects of the Conservation Practices . . . . . . . 106
7.4.5 Role of Check Dam in Reducing Soil
and Water Loss . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 107
7.4.6 Future Research Scenarios . . . . . . . . . . . . . . . . . . . . . 108
7.5 Conclusions . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 109
References . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 109
8 Sediment-Storage Effects of Check-Dam System in the Small
Watershed . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 113
8.1 Relative Stability and Optimum Programming
of Check Dams on the Loess Plateau . . . . . . . . . . . . . . . . . . . . 113
8.2 Characteristics of the Yangdaogou Catchment . . . . . . . . . . . . . 117
8.3 Experimental Methods . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 118
8.3.1 Runoff Simulation . . . . . . . . . . . . . . . . . . . . . . . . . . . 119
8.3.2 Rainfall Simulation . . . . . . . . . . . . . . . . . . . . . . . . . . . 122
8.4 Results and Discussion . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 125
8.4.1 Mechanism of the Relative Stability Development . . . . 127
8.4.2 Further Research on the Theory of Relative
Stability . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 130
8.4.3 Comparison of Sediment Loss and Dam-Land
Area . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 132
8.4.4 Comparison of the Water Discharge and Sediment
Concentration . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 134
8.4.5 Relationship Between the Dam-Land Increase
and Erosion Reduction . . . . . . . . . . . . . . . . . . . . . . . . 136
Contents
xix