**3.2.5 Housing damage assessment results**

The housing damage scope and extent of loss were defined again by integrating field investigation data, data reported by local government (Figure 21). This is the first time satellite-airplane-ground integration assessment mode used in national disaster assessment. The damage scope was partitioned into three parts: collapsed building area, about 1,314,000m2; serious damaged building area, about 2,332,000 m2; and minor damaged building area, about 680,000 m2. Collapsed building is defined as houses collapsed into ruins; serious damaged building as structures of houses been destroyed, thus it must be reconstructed; minor damaged building as structure been slightly affected, and it can still be used after reinforcement. Figure 8 and table 1 show housing damage assessment results. Figure 22 illustrates the remote sensing hazard monitoring and assessment flow in Yushu Earthquake.

High Resolution Remote Sensing Images Based Catastrophe Assessment Method 193

Buildin g

Residential 118.5 1.6 120.1 27.8 116.6 31.2 147.8 34.2 27.7 8.5 36.2 8.4 Office 0.8 4.9 5.7 1.3 3.8 62.7 66.5 15.3 4.2 17.3 21.5 4.9 School 0.7 0 0.7 0.2 0.2 1.4 1.6 0.4 0 0.9 0.9 0.2

Special 4 0.2 4.2 1.0 8.9 1.4 10.3 2.4 5.4 0.5 5.9 1.4 Total 124.1 7.3 131.4 30.4 131.7 101.5 233.2 53.9 37.9 30.1 68 15.7

Table 2. Housing damage construction area statistic table of Jiegu town urban area.

Serious damage (ten thousand square meters, %)

0.1 0.5 0.6 0.1 2.2 4.8 7 1.6 0.6 2.9 3.5 0.8

Total Ratio Bungal

ow

Minor damage (ten thousand square meters, %)

Total Ratio

Buildin g

Collapse & damage

Industrial and mining enterprises Bungalo w

**3.3 Zhouqu debris flow** 

Completely collapsed (ten thousand square meters, %)

Total Ratio Bungal

Fig. 22. Remote sensing hazard monitoring and assessment flow

road, making disaster relief a very difficult task.

On August 8th 2010, a serious debris flow disaster occurred in Zhouqu County, Gannan Tibetan Autonomous Prefecture, Gansu Province, and China. The debris flow breaks many records since 1949, including number of death, extent of damage, and relief difficulty. The casualty consists of 1447 deaths, 318 missing, and about 21000 residents were forced to evacuate by p.m.4, August 24th. The disaster lasted for a long time, and repeatedly occurred in some regions, resulting in several barrier lakes, and part of town under water. After 8th, the disaster area had suffering from several heavy rains, which, triggered more debris flow, and interrupted the traffic. The hard-hit region was in remote mountain area with narrow

ow

Buildi ng

type

Fig. 20. Disaster scope assessment map of Yushu Earthquake

Fig. 21. Housing damage assessment results



Table 2. Housing damage construction area statistic table of Jiegu town urban area.

Fig. 22. Remote sensing hazard monitoring and assessment flow

#### **3.3 Zhouqu debris flow**

192 Remote Sensing – Applications

Fig. 20. Disaster scope assessment map of Yushu Earthquake

Fig. 21. Housing damage assessment results

On August 8th 2010, a serious debris flow disaster occurred in Zhouqu County, Gannan Tibetan Autonomous Prefecture, Gansu Province, and China. The debris flow breaks many records since 1949, including number of death, extent of damage, and relief difficulty. The casualty consists of 1447 deaths, 318 missing, and about 21000 residents were forced to evacuate by p.m.4, August 24th. The disaster lasted for a long time, and repeatedly occurred in some regions, resulting in several barrier lakes, and part of town under water. After 8th, the disaster area had suffering from several heavy rains, which, triggered more debris flow, and interrupted the traffic. The hard-hit region was in remote mountain area with narrow road, making disaster relief a very difficult task.

High Resolution Remote Sensing Images Based Catastrophe Assessment Method 195

The flooded area expanded obviously (Figure 26), with about 226,000 m2 in August 15th, 23,000 m2 more compared with that in August 10th, and 102,000 m2 more compared with that

Fig. 24. Debris flow and landslide monitoring map

Fig. 25. Settlement monitoring map

in May 5th.

#### **3.3.1 Preliminary assessment**

An UAV and airplane were sent to Zhouqu one day after the debris to acquire affected area images, including UAV image of 0.2m resolution and aerial remote sensing images of 1m resolution. Once the images were sent back, we compared pre-disaster and post-disaster remote sensing images, continually monitored disaster scope, damage extent of housing, residents , variation of river water level, newly happened landslide, and preliminary analyzed and estimated the damage condition and disaster trend.

Figure 23 illustrates preliminary assessment result. Collapsed area was 0.14 km2, among which more than 90% were bungalows; serious damaged area was 0.15 km2, among which more than 79% were buildings; minor damaged area was 1.12 km2, among which more than 40% were buildings. Affected crop area was about 0.45 km2, and affected forest area was about 0.27 km2.

Fig. 23. Preliminary assessment results of Zhouqu Debris Flow disaster

According to debris flow and landslide monitoring result (Figure 24), Sanyanyu debris flow area was 0.66 km2; Luojiayu debris flow area was 0.2 km2. The 5 landslide regions in the mountain area of Zhouqu had a total area of 17272 km2.

Figure 25 and Table 3 shows refugee settlement monitoring result. Tents number increased a lot from August 15th to August 8th.


Table 3. Comparison of tents number

An UAV and airplane were sent to Zhouqu one day after the debris to acquire affected area images, including UAV image of 0.2m resolution and aerial remote sensing images of 1m resolution. Once the images were sent back, we compared pre-disaster and post-disaster remote sensing images, continually monitored disaster scope, damage extent of housing, residents , variation of river water level, newly happened landslide, and preliminary

Figure 23 illustrates preliminary assessment result. Collapsed area was 0.14 km2, among which more than 90% were bungalows; serious damaged area was 0.15 km2, among which more than 79% were buildings; minor damaged area was 1.12 km2, among which more than 40% were buildings. Affected crop area was about 0.45 km2, and affected forest area was

analyzed and estimated the damage condition and disaster trend.

Fig. 23. Preliminary assessment results of Zhouqu Debris Flow disaster

mountain area of Zhouqu had a total area of 17272 km2.

Settlement Area (m2) Tents number in 8th

lot from August 15th to August 8th.

Table 3. Comparison of tents number

According to debris flow and landslide monitoring result (Figure 24), Sanyanyu debris flow area was 0.66 km2; Luojiayu debris flow area was 0.2 km2. The 5 landslide regions in the

Figure 25 and Table 3 shows refugee settlement monitoring result. Tents number increased a

Tents number in

15th August Increasing number

August

No.1 high school 2079 13 55 42 No.3 high school 3590 36 98 62 total 5669 49 153 104

**3.3.1 Preliminary assessment** 

about 0.27 km2.

Fig. 24. Debris flow and landslide monitoring map

Fig. 25. Settlement monitoring map

The flooded area expanded obviously (Figure 26), with about 226,000 m2 in August 15th, 23,000 m2 more compared with that in August 10th, and 102,000 m2 more compared with that in May 5th.

High Resolution Remote Sensing Images Based Catastrophe Assessment Method 197

First level includes 3 categories of 59 grids: seriously damaged area, seriously flooded area,

The disaster scope and damage extent were defined again by integrating pre-disaster, postdisaster remote sensing information, ground investigation data and data reported by local

Disaster area was partitioned into three parts: serious affected region refers to the regions which bore main force of landslide, resulting in serious damage to houses, infrastructure and farmland; severe affected area refers the region which suffered from a long time soaked in water and mud, causing damage to houses; minor affected region refers to the region

The serious affected area was 1.2 km2, severe affected area was 0.2 km2 and minor affected

In the following Physical Quantity Assessment process, with the help of data reported by local government, we carefully assessed the physical quantity of houses, roads, power facilities, communication facilities, water conservation facilities, municipal utilities and land resources in UAV and airborne images to estimate approximate direct economic loss. It is worth to mention that some damage quantity ignored in field investigation was detected in remote sensing images, such as submerse street trees, telegraph poles, smart street pavilions. According to remote sensing images and ground investigation verification result (Figure 29), in rush destroyed region, collapsed residential building area was about 125,000 m2, seriously damaged area was about 102,000 m2, minor damaged area was about 147,000 m2. In flooded

where houses and infrastructures are mildly damaged by floods and landslides.

Fig. 28. Disaster scope assessment map of Zhouqu debris flow disaster

**3.3.4 Physical quantity assessment** 

region, collapsed building area was around 419,827 m2.

and minor affect area; Second level includes 2457 subgrids.

**3.3.3 Disaster scope and housing damage assessment** 

government (Figure 28).

area was 1.0 km2.

Fig. 26. Water area monitoring map

#### **3.3.2 Ground investigation**

Then according to the preliminary analysis results, we partitioned affection area into 2-level grids similar with previous case, using house as unit in high-resolution UAV and airborne remote sensing images. A total of 2457 girds were indexed (Figure 27). Hazard assessment experts were sent for field investigation. The damage extent, building size, architectural style, and field pictures of each grid were collected and sent back to experts in NDRCC for interpretation and verification.

Fig. 27. Field investigation grids partition map

First level includes 3 categories of 59 grids: seriously damaged area, seriously flooded area, and minor affect area; Second level includes 2457 subgrids.

#### **3.3.3 Disaster scope and housing damage assessment**

196 Remote Sensing – Applications

Then according to the preliminary analysis results, we partitioned affection area into 2-level grids similar with previous case, using house as unit in high-resolution UAV and airborne remote sensing images. A total of 2457 girds were indexed (Figure 27). Hazard assessment experts were sent for field investigation. The damage extent, building size, architectural style, and field pictures of each grid were collected and sent back to experts in NDRCC for

Fig. 26. Water area monitoring map

**3.3.2 Ground investigation** 

interpretation and verification.

Fig. 27. Field investigation grids partition map

The disaster scope and damage extent were defined again by integrating pre-disaster, postdisaster remote sensing information, ground investigation data and data reported by local government (Figure 28).

Disaster area was partitioned into three parts: serious affected region refers to the regions which bore main force of landslide, resulting in serious damage to houses, infrastructure and farmland; severe affected area refers the region which suffered from a long time soaked in water and mud, causing damage to houses; minor affected region refers to the region where houses and infrastructures are mildly damaged by floods and landslides.

The serious affected area was 1.2 km2, severe affected area was 0.2 km2 and minor affected area was 1.0 km2.

Fig. 28. Disaster scope assessment map of Zhouqu debris flow disaster
