| With the rapid development of urbanization and the increasing impervious surface area, the hydrological condition of city area has been changed greatly. The increase of runoff volume and peak flow makes the municipal drainage pipe network under great pressure and leads to the city flooding risk. Therefore, the urban storm water facilities should be developed actively. If the water is saved during the rainfall, not only the risk of flooding can be reduced, but also the rainwater resources can be used fully.After the rainfall data of Tianjin was collected and the characteristics of the rainfall of the city were analyzed, the feasibility of the development and construction of the storm water retention pond was determined. Storm water management model(SWMM) developed by Environmental Protection Agency(EPA) was used to simulate a 1.125km2 region in Tianjin. The area was divided into 8 catchment subdomains and water pipeline system was simplified. Whether urbanized or not were compared in simulation during different storm return period, the results showed total amount of export runoff volume and peak flow were obviously increased, comparing with that before urbanization.In view of the simulation region whose catchment area was 1.125km2, by the construction of storm water retention pond, the hydrological condition after regional development and construction should be closed with the natural state before development.(The hydrological indices should include total runoff volume, peak flow rate and runoff coefficient.) Therefore, the retention pond should be set at the end of the regional pipe network and in front of the outlet, so that the storm water began to drain out after the pond was full. The type of pond that this paper referred to was intended to be built as an underground enclosed storm water retention pond, which was not provided with biological treatment functions and could only play a role of storing storm water runoff in a short period.The capacities of the retention ponds calculated by designed return period 1a, 2a, 5a were 16910m3, 27850m3, 40030m3, respectively. The three calculated capacities were input in the model and simulated to analysis the improvement of researched area's hydrological effect. About the retention pond calculated by 2a, it could make the runoff coefficient be back to close with status of the area before urbanization and the relative runoff coefficient be close to ideal figure 1. The improvement of runoff coefficient was remarkable. When the rainfall of return period 2a occurred, the reduction of total runoff volume and peak flow rate could reach 52.9% and 60.5% because of this pond, respectively. When the rainfall beyond the return period 2a occurred, the total runoff volume could be reduced to a certain degree by this pond, but the reduction rate of the peak flow rate was less than 11%. When the big return period(10a, 20 a, 50a) rainfall occurred, for the influence on the runoff coefficient and total runoff volume, the pond calculated by 5a was better than the pond calculated by 2a. But for the high frequency small return period rainfall situation, it had an over impact on the different hydrological indices so that the indices had large differences with those before urbanization. When small return period rainfall occurred, the pond calculated by 1a had a wonderful performance on improving hydrological indices. But it was not efficient as two bigger ones when the big return period storm appeared because of its capacity. Through the comparison of the model, it was reasonable to calculate the pond's capacity based on return period 2a. For the problem of peak flow reduction, it could be resolved by establishing drainage outlet at the bottom of the retention pond. |
PDF Full Text Request