## 3 Results and Discussions
### The Importance of Non-Geological Methods in Urban Flood Control  
In addition to the geological methods mentioned above, there are non-geological methods such as river drainage, reservoir and lake water storage and underground drainage pipe network system storage to prevent and control flood disasters. These methods applicable to the study area are discussed below. 1. Flood discharge capacity of the river channel  
The flood is mainly discharged in the Jialu River and its tributaries, which eventually flow into its main stream and discharge outward in the downstream Zhongmu County. The flood discharge capacity can be characterized by the overcurrent capacity of the Zhongmu hydrological station. According to the calculation of the warning water level of the Zhongmu Hydrological Station of the Jialu River at 77.5 m, the total drainage capacity of the river channel for floods is 323 m\({}^{3}\)/s [34], and the flood drainage capacity is 27.91 million m\({}^{3}\)/d, as shown in Table 5.
2. Water storage capacity of reservoirs, lakes, and wetlands  
The water storage capacity includes the storage capacity of reservoirs and lakes after the completion of the Jialu River source or upstream reservoir and the water ecological projects. After the completion of the urban water ecological project, the area of lakes and wetlands will increase to 107.25 km\({}^{2}\). In addition to the storage by this increased area of rivers, ditches, etc., and the ecological water demand for other lakes and wetlands under normal circumstances, about 62.57 million m\({}^{3}\) of flood control water storage can be reserved (see Table 5 for details). The total catchment area of the Jialu River source or upstream reservoir is 786 km\({}^{2}\), and the total storage capacity is about 260.9 million m\({}^{3}\). But, after years of sediment deposition, the current storage capacity has been reduced to 195.68 million m\({}^{3}\). In fact, the storage capacity of the reservoir for rainwater is positively correlated with the rainfall and the catchment area. Only when the rainfall intensity reaches a certain level will the reservoir reach the maximum storage capacity, which is 195.68 million m\({}^{3}\). The calculations for the storage capacity of the reservoir for rainwater under different rainfall intensities are shown in Table 5.  
Storage capacity of underground drainage network system  
The study area plans to build a new underground pipe network of 2576 km. With the completion of this project, the total length of the pipe network will increase from 1831 km to 4407 km. With that, the water storage capacity of the underground pipe network will increase from 3.24 million m\({}^{3}\) to 7.79 million m\({}^{3}\), as shown in Table 5.  
The flood control capacity of Zhengzhou using geological and non-geological methods shown in Tables 4 and 5 are estimations based on the results obtained after the completion of the various projects for the Jialu River. These include the comprehensive treatment project, construction of the sponge city, and implementation of various projects that employ the concepts of ecological and geological aspects. It is to be noted that the geological method does not include the flood control capacity obtained by using underground space to build water storage projects. Based on the relevant data in Tables 4 and 5, the proportion of the geological method's ability in flood control was calculated. The calculation was based on the formula expressed as the proportion of the ability of geological methods to remove floods = (the amount of flood water removed by geological methods)/(the amount of flood water removed by geological methods + the amount of flood water removed by non-geological methods) \(\times\)100%. The results of the calculations are shown in Table 6.