Calculation Method of Short Duration Rainstorm Intensity Formula Considering Non-Stationarity of Rainfall Series: Impacts on Simulation of Urban Drainage System

The changing nature of the earth's climate and rapid urbanization lead to the change of rainfall characteristics in urban areas, and the stability of rainfall series is destroyed, it is a difficult challenge to consider this change in urban drainage simulation. A variety of methods are used to test the stationarity of annual maximum rainfall intensity series of Zhengzhou meteorological station from 1981 to 2010, and the intensity-duration-frequency (IDF) curves of changing environment are fitted by GAMLSS model and further generalized into short duration rainstorm intensity formula. The 3-hour design rainstorm in different scenarios was used as the input of Mike Flood model to simulate the operation of the campus drainage system of Zhengzhou University. Results indicated that: The rainfall series is non-stationary and has an increasing trend. Although the parameters of the short duration rainstorm intensity formula have no fixed change rules, there are traces to follow in the design rainstorm. According to Mike Flood model, the non-stationary scenario provides a series of dangerous signals such as more flood volume, larger inundation area, higher flood depth and slower recession process. The flood volume of the non-stationary scenario is 23.5% more than that of the stationary scenario, and the inundated area is 18.5% more when the return period is 5 years. In the future, the difference is 34.0% and 24.6% respectively, and it can reach more than 50% when the return period is once in two years. We will discuss the non-stationarity and challenges brought about by changing environments.

FORECASTING THE RISK OF FLOODING WHEN THE PAC CAP HYDROPOWER DAM BREAKS ON NA RI RIVER IN BAC KAN PROVINCE

Thủy điện Pác Cáp được phê duyệt chủ trương đầu tư tại Quyết định số 96/QĐ-UBND ngày 18/01/2018 trên sông Na Rì, huyện Na Rì tỉnh Bắc Kạn với công suất 6 MW. Trong quá trình thi công, vận hành 02 tổ máy, vỡ đập có thể xảy ra khi lũ tràn đỉnh đập, nứt ngang nứt dọc đập, trượt mái thượng và hạ lưu đập,… Nghiên cứu này tập trung mô phỏng sự cố vỡ đập thông qua việc sử dụng mô hình Mike Flood. Kết quả chỉ ra rằng: chiều sâu ngập lớn nhất >10 m với diện tích ngập lụt khoảng 15 ha trong đó chủ yếu là đất trồng cây hàng năm, đất lúa và rừng sản xuất; chiều sâu ngập từ 4-10 m chiếm khoảng 10 ha; chiều sâu từ 1-4 m ngoài các loại đất rừng và đất nông nghiệp bị ngập còn nhấn chìm khoảng 30 ngôi nhà của xã Lương Thành và Lam Sơn thuộc huyện Na Rì và một số công trình hạ tầng khác. Kết quả nghiên cứu là cơ sở đưa ra các biện pháp phòng tránh nhằm giảm thiểu tác hại đến vùng hạ lưu công trình, đồng thời cũng là căn cứ để xác định trách nhiệm của Nhà máy trong quá trình bồi thường nếu để sự cố xảy ra.

Urban flood modelling in Qiqihar city based on MIKE flood

Qiqihar is a significant city on the Nen River in China, which is the main stream of the Songhua River basin. The length of the return period of Qiqihar's flood control design standard is fifty years. If a 100-year flood event happened, Qiqihar would face the risk of a burst levee. To quantitatively evaluate flood risk to the city from a burst levee or proactive flood diversion, a model for analysing flood submergence from a burst levee in the City of Qiqihar is established based on MIKE Flood. The model integrates one- and two-dimensional hydrodynamic models to implement coupled simulation. The terrain data are from city elevation data on a scale of 1:10 000. Following local modifications made based on survey data, such as on levees, roads, and buildings, a 20 m × 20 m grid of terrain data was formed as the terrain input of the model. The model simulates the water level of Nen River and the flood path, submerged time/depth/area, and duration in floodplain under three scenarios: baseline, proactive downstream flood diversion, and an upstream levee burst under a flood with a one hundred-year return period. Proactive downstream flood diversion can reduce the maximum water level by 0.068 m and correspondingly decrease peak flood flow by 1120 m3 s−1. These results provide basic information to support urban flood risk analysis and flood dispatching and management across the whole river basin.

Numerical Study on the Impact of Revising the Rainstorm Intensity Formula on the Storm Flood Disaster Prediction in Huinan, Pudong District

The numerical model by MIKE FLOOD software has been set up with coupled the rainfall runoff sub-model and underground network sub-model by MIKE URBAN software and the overland flow sub-model by MIKE 21 software to simulate the storm flood in Huinan, Pudong District. After the calibration and validation, the model is applied to study the impact of revising the rainstorm intensity formula on the local storm flood disaster prediction. And the conclusions are obtained: after the formula revised, the time to appear the maximum waterlogging area would be delayed, and the local storm flood disaster would worsen under the current drainage pipe networks, i.e., the overland flood range and its depth would slightly increase.