## 3 Results and Discussions
### The Role of Geological Methods in Urban Flood Control
Assessment of rainwater infiltration and storage capacity in the study area based on the geological method-integrating sponge city construction with hydrogeology  
The rainwater storage capacity of the vadose zone soil layer is closely related to the rainfall intensity, the permeability coefficient of the vadose zone soil layer, the thickness of the vadose zone, the depth of rainfall infiltration, the effective water inflow rate, and the distribution area of each soil layer. Among them, the permeability coefficient determines whether rainwater under different intensities can infiltrate into the vadose zone, and the thickness of the vadose zone determines whether there is enough space to accommodate rainfall; the depth of rainfall infiltration, effective water inflow rate, and distribution area of each soil layer determine whether the soil layer in the vadose zone can accommodate rainfall of different intensities. Based on the previous experimental data, we have obtained the permeability coefficient, vadose zone depth, effective water inflow rate and other parameters of soil layers with different rock types in the study area. Through analysis, we have found that as long as there is sufficient rainfall infiltration depth, the study area has extremely strong rainfall storage capacity. Next, this article will evaluate the rainwater storage capacity of the study area based on the concept of sponge city engineering and hydrogeological integration by restoring the rainfall intensity and infiltration depth at different return periods. Rain intensity and return periods  
Since many aspects of urban waterlogging risk prevention and control involve parameters such as rainfall intensity and its return period, the methods used for their calculation are very important. This paper uses the following formula selected by the \"720\" disaster investigation group of the State Council:  
\[\text{R}=((2479.78+2388.2762\times\text{lgp})/(\text{t}+15.3)^{0.775})\times 8.64 \tag{3}\]  
where R is the is the rainfall (mm/d) at different return periods (rainfall intensity), p is the return period (year), and t is the rainfall duration (1440 min). The rain intensities of different return periods calculated by the above formula are given in Table 4. \begin{table}
\begin{tabular}{c c c c c c c} \hline \hline \multirow{2}{*}{**Soil Mass Types**} & **Light** & **Moderate** & **Heavy** & **Rainstorm** & **Heavy** & **Extremely** \\  & **Rain** & **Rain** & **Rain** & **(100 mm/d)** & **Rainstorm** & **Rainstorm** \\  & **(10 mm/d)** & **(25 mm/d)** & **(50 mm/d)** & **(250 mm/d)** & **(250 mm/d)** & **(-250 mm/d)** \\ \hline silty clay & 141 & 353 & 706 & 1412 & 3531 & \textgreater{}3531 \\ silt or loess-like soils & 76 & 190 & 381 & 762 & 1904 & \textgreater{}1904 \\ silty-fine sand & 85 & 212 & 424 & 848 & 2120 & \textgreater{}2120 \\ medium sand & 83 & 206 & 412 & 825 & 2062 & \textgreater{}2062 \\ coarse sand & 76 & 190 & 379 & 759 & 1879 & \textgreater{}1879 \\ \hline \hline \end{tabular}
\end{table} 
Table 3: Thickness of vadose zone soil required by different strata for different rainfall intensity. \(\hat{\texttt{2}}\) Infiltration depth of rainfall and rainfall storage capacity of soil layer in vadose zone According to the existing research results [31], the formula for calculating the rainfall infiltration depth (H) in the study area is as follows:  
\[\text{H}=0.8905\text{R}+0.79\ \text{(medium $-$ coarse sand)} \tag{4}\]  
\[\text{H}=0.4951\text{R}+4.47\ \text{(silt, silty clay)} \tag{5}\]  
\[\text{H}=0.7647\text{R}+0.74\ \text{(silty fine sand)} \tag{6}\]  
The formula for calculating the rainwater infiltration and storage capacity Q of the vadose zone soil layer is as follows:  
\[\text{Q}=\text{H}\times\text{S}\times\text{N}_{\text{e}} \tag{7}\]  
where Q is the infiltration and storage capacity of the vadose zone soil layer (m\({}^{3}\)); H is the rainfall infiltration depth (m), and S is the distribution area of soil layers with different lithologies (m\({}^{2}\)).