Development Characteristics and Risk Assessment of the Damogou Debris Flow in Mentougou District, Beijing

doi:10.19657/j.geoscience.1000-8527.2022.086

Abstract

Abstract:

Debris flow is one of the most common types of geological disasters in western and northern Beijing mountainous areas during stormy seasons. In the history of Damogou Gully (Qingshui town, Mentougou district, Beijing), there were many periods of debris flow disasters. At present, there are still many artificial deposits and collapse accumulations that constitute a potential debris flow source, and there are serious debris flow hidden dangers. This study identifies the types of debris flow sources, their storage and distribution, simulates the debris flow impact range under the frequency of once every 10, 20, 50 and 100 year rainfall, and evaluates their respective risk. The results show that the potential debris flow source is mainly man-made waste slag and coal gangue, with the residual reserve of ~447,000 m³. The high-risk debris flow area accounts for 13.1%-20.0%, mainly distributed in the gully mouth accumulation area and the confluence of main and branch gullies. The proportion of medium-risk area is 29.9%-31.2%, and the proportion of low-risk area is 48.8%-57.0%. It is advisable to set up prevention and control measures of upstream interception and downstream drainage in the circulation area of Damogou gully, and strengthen the rainfall monitoring and warning in the formation area in the heavy rainfall seasons.

Key words: debris flow, Damogou Gully, FLO-2D, numerical simulation, risk assessment, Mentougou district, Beijing

CLC Number:

P642.23

NIE Qiong, NIE Zhibao, CHEN Jian, DING Shijun, WU Saier, LI Duo, GE Runze, CHEN Ruichen. Development Characteristics and Risk Assessment of the Damogou Debris Flow in Mentougou District, Beijing[J]. Geoscience, 2023, 37(04): 1013-1022.

Figures/Tables 14

Fig.1 Geographical location map of the Damogou Gully drainage area in Beijing

Fig.2 Data format processing flowchart

Table 1 Reference information on the Manning coefficient (n) range

地表条件	n值	地表条件	n值
极为茂密草地	0.17~0.80	耕地	0.008~0.012
茂密草地	0.17~0.48	无农作物的休耕地	0.008~0.012
灌木或牧草地	0.30~0.40	传统耕地	0.06~0.22
一般草地	0.20~0.40	已修整农地	0.06~0.16
覆盖较差的粗糙地	0.20~0.30	梯田	0.30~0.50
矮草原	0.10~0.20	无耕作且无上期农作物	0.04~0.10
稀疏植被地	0.05~0.13	无耕作、上期农作物存有	(20%~40%) 0.07~0.17
无植被覆盖	0.09~0.34	无耕作、上期农作物存有	(60%~100%) 0.07~0.47
20%植被覆盖	0.05~0.25

Table 2 Reference information on the range of laminar flow arrest coefficient

地面条件	K值范围	地面条件	K值范围
混凝土/沥青	24~108	稀疏植被	1000~4000
裸露砂土	30~120	矮草原	3000~10000
级配土	90~400	早熟禾属植物草地	7000~50000
被侵蚀的黏性土	100~500

Table 3 Relationship between total source reserve and dynamic reserve

总物源储量V(万m³)	动储量W(万m³)
V<50	W=0.15V
50<V<100	W=0.3V
100<V<200	W=0.37V
V>200	W=0.4V

Fig.3 Location map of Damogou Gully water collection spots

Table 4 Water collection spot flow chart under each grade of rainfall frequency in Damogou Gully

降雨频率(%)	汇水面积(km²)	径流系数	降雨强度 (mm/h)	清水流量 (m³/s)	泥石流峰值流量(m³/s)
10	1.566	0.35	49	17.68	41.30
5	1.566	0.35	58	22.39	51.72
2	1.566	0.35	68	27.68	63.93
1	1.566	0.35	80	34.37	79.40

Fig.4 Debris flow velocity distribution maps of different rainfall frequencies at hidden debris flow spots in Damogou Gully

Table 5 Statistics of simulation results

降雨频率 /%	最大堆积深度(m)	影响范围 (m²)	堆积方量 (m³)	平均堆积深度(m)
10	10.82	113500	289080.225	2.546962
5	14.21	116225	315447.450	2.714110
2	16.25	119375	347857.725	2.913991
1	17.20	124825	386111.300	3.093221

Fig.5 Distribution maps of debris flow depth under different rainfall frequencies of debris flow potential spots in Damogou Gully

Table 6 Basis for debris flow risk determination

危险分级	最大泥深(m)	逻辑关系	最大泥深×最大流速(m²/s)
高	$H ≥ 4.0$	OR	$V H ≥ 8.0$
中	$1.5 ≤ H ≤ 4$	AND	$3 ≤ V H ≤ 8.0$
低	$0 < H < 1.5$	AND	$V H < 3$

Table 6 Basis for debris flow risk determination

危险分级	最大泥深(m)	逻辑关系	最大泥深×最大流速(m²/s)
高	$H ≥ 4.0$	OR	$V H ≥ 8.0$
中	$1.5 ≤ H ≤ 4$	AND	$3 ≤ V H ≤ 8.0$
低	$0 < H < 1.5$	AND	$V H < 3$

Table 7 Characteristics of each hazard zone

危险性分区	特点
高危险区	泥石流破坏性极强,可以破坏建筑,建筑内外均存在危险
中危险区	房屋建筑受到一定程度破坏,但室内属于安全区,室外属于危险区
低危险区	泥石流强度较低,对人和物都不会造成较大损害

Table 8 Risk zoning result

降雨频率(%)	危险性分区	面积(m²)	比例(%)
10	低危险区	64725	57.03
	中危险区	33900	29.87
	高危险区	14875	13.11
5	低危险区	63000	54.21
	中危险区	35550	30.59
	高危险区	17675	15.21
2	低危险区	60950	51.06
	中危险区	37150	31.12
	高危险区	21275	17.82
1	低危险区	60900	48.79
	中危险区	39000	31.24
	高危险区	24925	19.97

Fig.6 Debris flow risk zoning map of hidden danger spots under different rainfall intensities in Damogou Gully

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