Water damage to the Kizil grottoes is primarily manifested in erosion by rainwater and surface runoff from the rock. The climate of the Xinjiang area is characterized as arid with low precipitation. The annual precipitation of the Heizi area is only 94.9 mm, and most of the rainfall occurs in June, July, and August. Because there is no soil, surface runoff occurs immediately during heavy rainfall. This water exerts a strong eroding force on the cliff rock, with numerous gullies of different sizes forming rapidly, some reaching several tens of meters in depth. These gullies create the greatest danger of collapse to the grottoes.
From the top of the grottoes, the gullies present a crisscross pattern. In the western region of the valley alone there are nineteen gullies of different sizes, five of which were directly endangering the caves, either undermining the bases or eroding the tops of the cliffs. Moreover, new gullies are developing constantly.
Under present conditions, it is difficult to eliminate the danger of erosion completely. The current policy is to treat gullies that are directly threatening or directly eroding the caves. In the course of conducting a comprehensive survey of the gullies, a portion of an ancient sandstone brick wall was discovered in the fore portion of the top of the cliff in the western region of the valley. The direction of the wall was essentially parallel to the cliff face. It was presumed by the Guizi Grotto Research Institute that this wall may have been built in ancient times to divert sand and floodwaters. If a new water-diversion wall were to be constructed at the top of the cliff in imitation of this ancient method, its position would have to be moved to the rear. However, this still would not solve the drainage problem on the front slope. Therefore, interception, diversion, and conveyance of the surface runoff away from the caves in accordance with the different specific conditions of each situation were adopted insofar as possible to eliminate severe erosion caused by runoff.
In section 1, the caves are very close together. Several key caves on the upper level are subjected to continuous erosion by runoff. The tops of Caves 14-17 were already very thin. Because rainwater often seeps into these caves, it was important to have a good drainage system. The principal method taken here was to dig a drainage ditch running east-west about 7-8 m from the top of Cave 9. The western end ran through the large gully in the eastern side of Caves 2-7 and the eastern end reached the large gully on the eastern side of Cave 17. The southern wall of the drainage ditch was high, and its other wall was low. In this way, it has intercepted the flow from the roof of the cliff in the north and diverted the
Flow into the gullies in the east and west. More than a year of study has shown that the results have been very good and that the drainage ditch successfully intercepted and diverted the flow.
It was difficult to build a retaining wall and drainage ditch on the front slope of the cliff top of section 2 caves. Instead, a reinforced concrete awning was built at a fixed height at the fore wall of the cliff. This served to prevent water from directly eroding the caves.
External awnings or shelter structures have been considered. The design should be simple and practical. Anchor bolts used to reinforce the cliff face could support the awning. However, aesthetically it would be best to integrate the awning style with the appearance of the caves and add arched or trapezoid-shaped figures.
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