Effect Of Low Impact Development Measures On Inundation Reduction

Low impact development(LID)involves measures with different use,such as emission reduction at source,control during the process and terminal disposal.And flood simulation model is an effective tool for scheme comparison and selection of LID measures in the design stage,as well as for its effects evaluation after construction.In order to evaluate the impact of LID measures on the runoff and the spatial and temporal change of inundation distrilbution comprehensively,Flood Simulation Numerical Model and Flood Risk Analysis Software(FRAS)developed independently by IWHR are used in this study to evaluate the effect of individual and combined low impact development(LID)measures on inundation reduction at Jinan pilot area.In addition,the SCS method is added to the original rainfall-runoff model,which is intergrated with the 2D surface hydraulic model in real-time.Therefore,the software can reflect the runoff and confluence process more accurately.This study focus on the inundation reduction effect of combined and individual LID measures in sponge city pilot of Jinan,which is located in the Xinglong Area of Darming Lake Region.The combined LID measures are set according to The Implementation Plan to analyze the measures’ effect on flood reduction under the 24h design storm with 5-year,10-year and 20-year return period,total percipitation of which is 120.9,154.2 and 187.3mm respectively.The effects of LID measures on inundation area are all analyzed at pilot area,small watershed and block scale.And their effects on runoff volume and peak flow are also analyzed at small watershed scale.Moreover,three different rainfall patterns are set according to the 12h design rainstorms of Jinan to compare the effects of LID measures under different hyetographs,which are rainfall concentrated early in the storm,rainfall concentrated in the middle of the storm and rainfall concentrated at the end of the storm with 5-year,10-year and 20-year return period.The total 12h precipitation of different return period is 96.84,123.51 and 150.04mm respectively.And the effects of LID measures under different rainfall patterns on inundation area are analyzed at pilot area scale.And the changes of runoff volume and peak flow under different rainfall patterns are compared at watershed scale.In addition,individual LID measures of different sizes are also set in the Square West Ditch basin to compare and analyze their inundation reduction effect under the 24h design storm with 10-year return period.The simulation results indicate:(1)Combined LID measures can decrease the flooding area at pilot area,small watershed and block scale under all the 24h design storms with 5-year,10-year and 20-year return period.Besides,the total runoff volume and peak discharge are also reduced at watershed scale after implementing these measures.The effects of LID measures decrease with the increase of rainfall and are most significant under the 5-year return period storm,where the total runoff and peak discharge are cut respectively by 6.5%and 9.7%and the inundation area is cut by 48.96%in the measure-intensive block.(2)Individual LID measures have different effects under the 24h design storm with 10-year return period at basin scale.All measures can reduce inundation volume but it tends to increase at first and then decrease during the rainfall procedure.The effects on inundation area reduction are ranked as:sunken lawn,permeable pavement,green roof.Therefore,the individual LID measures should be set according to its applicability and functional characteristics.And different individual LID measures can be combined in a reasonable way to make them work with the best efficiency.(3)The effects of LID measures on total runoff reduction under different rainfall patterns with all three storm return periods are ranked as:rainfall concentrated in the early period,rainfall concentrated in the middle period,rainfall concentrated in the latter period.The reason is that the LID measures have more time to infiltrate the flood when the rainfall peak is later with a more gentle runoff procedure in earlier stage,which is better for LID measures to decrease the total runoff.However,the reduction effects on peak discharge are all ranked as:rainfall concentrated in the latter period,rainfall concentrated in the middle period,rainfall concentrated in the early period.This is because the LID measures are better for infiltration and flood retention in the early stage,so the peak discharge can be reduced more effectively when the rainfall peak is earlier.(4)Inundation reduction effect of LID measure is also closely related to the measure type and scale,terrain,underlying surface condition and setting location.It is necessary to have multi-scheme simulation as well as analysis through hydrological-hydraulic model when design the LID measures.In this study,the effect of LID measures on inundation reduction is based on the special topography and land use status of this study area,which has certain reference value for similar areas.And different topography,land use and hydraulic structures should be reasonable generalized for the actual application of flood simulation model.In addition,characteristics of specific LID measures should be considered to reasonably select the model parameters for simulation during the comparison of implementation schemes and effect evaluation for LID measures.