## 3 Results and Discussions
### The Role of Geological Methods in Urban Flood Control
N\({}_{\text{e}}\) is the effective porosity of the soil, which we define here as the difference between porosity and soil saturation. \(\hat{\texttt{3}}\) The rainwater storage capacity of the soil layer in the vadose zone of key study area  
The area of the key study area is 1945 km\({}^{2}\), of which 14% is green spaces and squares [32], and the area that can be used to build a sponge city is 272.30 km\({}^{2}\). According to the concept of integrating sponge city engineering and hydrogeological conditions, the soil layer in the aeration zone of green space and square land can be generalized as fine sand and silt layer, with an effective inflow porosity of 11.79%. Equation (7) is used to \begin{table}
\begin{tabular}{c c c c c c c c} \hline \hline  & & & & & **Bottom** & **The Increased** & \\  & & & & **Storage** & & **Storage** & \\
**Rainfall** & **Rainfall** & **Suburban** & **Capacity of** & **Capacity of** & **Capacity of** & **Capacity of** & **Capacity of** & **Total** \\
**Intensity/Return** & **Rainfall** & **Rainfall** & **Storage** & **Urban** & **Aquatic** & **Ecological** & **Restoration** & **(10\({}^{6}\) m\({}^{3}\))** \\
**Period** & **(mm/d)** & **(106 m\({}^{3}\)/d)** & **(10\({}^{6}\) m\({}^{3}\)/d)** & **Areas** & **Engineering** & **Reservoir at** & **the Source** & \\  & & & & & **(10\({}^{6}\) m\({}^{3}\)/d)** & **(10\({}^{6}\) m\({}^{3}\)/d)** & **(10\({}^{6}\) m\({}^{3}\)/d)** & \\ \hline Light rain & 10 & 27.50 & 5.62 & 2.69 & 14.53 & 3.28 & 26.12 \\ (upper limit) & & & & & & & \\ Moderate rain & & & & & & & \\ (upper limit) & 25 & 68.75 & 12.47 & 6.38 & 14.53 & 3.28 & 36.66 \\ Heavy rain & & & & & & & \\ (upper limit) & 50 & 137.5 & 23.89 & 12.51 & 14.53 & 3.28 & 54.21 \\ Once a year & 76 & 209.00 & 35.77 & 18.90 & 14.53 & 3.28 & 72.48 \\ Rainstorm & & & & & & & \\ (upper limit) & 100 & 275.00 & 46.74 & 24.79 & 14.53 & 3.28 & 89.34 \\ Once in 3 years & 111 & 305.25 & 51.77 & 27.49 & 14.53 & 3.28 & 97.07 \\ Once in 5 years & 127 & 349.25 & 59.07 & 31.42 & 14.53 & 3.28 & 108.30 \\ Once in a decade & 149 & 409.75 & 69.12 & 36.82 & 14.53 & 3.28 & 123.75 \\ Once in 30 years & 184 & 506.00 & 85.11 & 45.41 & 14.53 & 3.28 & 148.33 \\ Once in 50 years & 200 & 550.00 & 92.42 & 49.34 & 14.53 & 3.28 & 159.57 \\ Once in a century & 222 & 610.50 & 102.47 & 54.74 & 14.53 & 3.28 & 175.02 \\ Once in 200 years & 244 & 671.00 & 112.52 & 60.14 & 14.53 & 3.28 & 190.47 \\ Heavy rainstorm & & & & & & & \\ (upper limit) & 250 & 687.50 & 115.26 & 61.61 & 14.53 & 3.28 & 194.68 \\ Once in 500 years & 273 & 750.75 & 125.77 & 67.26 & 14.53 & 3.28 & 210.84 \\ Once in a millennium & 295 & 811.25 & 135.82 & 72.66 & 14.53 & 3.28 & 226.29 \\ The 3-day rainfall of the “720” & 617.1 & 1697.03 & 285.08 & 152.21 & 43.59 & 3.28 & 484.16 \\ \hline \hline \end{tabular}
\end{table} 
Table 4: Geological methods for assessing the drainage capacity of rainwater and floods in the study area. estimate the rainwater seepage storage capacity of the vadose zone soil layer, as shown in Table 4.  
4 The rainwater storage capacity of the soil layer in the vadose zone of the suburban area after investigation, it was found that the suburban area of the study area is 805 km\({}^{2}\), and rainfall cannot penetrate areas such as roads, urban buildings and factories, accounting for 22.375% of the suburban area. The underlying surface of other areas in the suburb is farmland, forest, and grasslands with good permeability. The area of vadose zone lithology with silty fine sand accounts for 48.89%, medium-coarse sand accounts for 15.88%, and silt and silty clay accounts for 35.23% (see Figure 9 for details). According to the method discussed earlier, the rainwater infiltration and storage capacity of the soil layer in the vadose zone in the suburbs were obtained (Table 4). 3.3.2.