Study On The Evaluation Of The Effect Of Low Impact Development Rainwater System Based On Landscape Ecology

The urban hydrological process is the core of the urban landscape pattern and water environment response mechanism.With the increase of urban impervious landscape types,the infiltration of urban rainfall and runoff decreases,and rainwater runoff is the main driving force for surface pollutants migration and transformation to a certain extent,the quality of urban water bodies is reduced.The construction of the sponge city has influenced the evolution direction of the urban ecological pattern.The LID facility is an important carrier that affects the evolution of the landscape ecological pattern and the link between the landscape pattern evolution and the ecological process.Therefore,it is necessary to combine the control mechanism of LID facilities on stormwater runoff,and use the landscape index to analyze the pattern of LID facilities to establish the relationship between landscape pattern and hydrological response.This study is based on the SWMM model,which simulates the field rainfall runoff control effect and peak flow reduction in the design rainfall conditions of the LID design plan in the study area.Six landscape indexes,including Shannon's diversity index,Shannon's evenness index,Patch Density,DIVISION,Largest patch index,Patch size coefficient of variation,were selected to analyze their corresponding design options,rainfall runoff control rate and peak flow reduction The relationship between the rate and the applicability of the landscape index to evaluate the effect of the LID landscape type,and the evaluation method of the effect of the LID scheme at the landscape level.Under different rainfall conditions,Shannon's diversity index,Shannon's evenness index,Patch Density,DIVISION,Largest patch index,Patch size coefficient were used to evaluate the effectiveness of LID landscape type effects.According to the limitations of the existing landscape index evaluation of LID landscape type,based on the "source" and "sink" landscape theory,the LID hydrological process evaluation index is proposed,and the effect of the LID hydrological process evaluation index on the evaluation of LID landscape type is analyzed under different rainfall scenarios accuracy.The main conclusions are as follows:(1)In the case of determining the design target of annual total runoff control rate,different layout of lid facilities in the site will have a significant impact on the rainfall runoff control effect and peak flow reduction effect.Under the target of annual total runoff control rate,the control effect and peak flow reduction effect of the single facility volume unchanged scheme is better than that of the single facility volume changed scheme,so the layout of lid facilities should be homogenized in the design stage to improve the effect of runoff control.(2)Shannon's diversity index(SHDI)and Shannon's evenness index(SHEI)are significantly correlated with rainfall runoff control rate and peak flow reduction rate under different scenarios.When the volume of a single facility does not change,the total volume of facilities changes,the volume of a single facility changes,and the total amount of facilities also changes,Shannon's diversity index(SHDI)and Shannon's evenness index(SHEI)are significantly correlated It has a significant positive correlation with the rainfall runoff control rate and peak flow reduction rate.When the total amount of facilities of a single facility is constant and the volume changes,Shannon's diversity index(SHDI)and Shannon's evenness index(SHEI)have a significant negative correlation with the rainfall runoff control rate and peak flow reduction rate,so Shannon's diversity index(SHDI)and Shannon evenness index(SHEI)are opposite All the three cases have good evaluation significance.Patch density(PD)can only be used as an evaluation index when the number of utility patches between different schemes is not constant.(3)The evaluation ability of LPI,DIVISION and PSCV are different in three different situations.When the volume of a single facility does not change and the total amount of facilities changes,the DIVISION and PSCV show a better evaluation ability,and the strength of DIVISIOV is greater than PSCV;when a single facility has no change in volume and the total amount of facilities,the ability of DIVISIOV is greater than PSCV.Only the LPI showed a better evaluation ability when the total number of facilities was unchanged and the volume changed;when the volume of single facility was changed and the total number of facilities was also changed,the LPI,DIVISION and DIVISION of the biological detention pool showed a better evaluation ability.The corresponding index should be selected according to the corresponding situation when evaluating the deployment effect of lid facilities by using the level index of facility patch type.(4)With the change of the rain peak coefficient and the duration of rainfall,the correlation coefficient between the landscape index and the rainfall runoff control rate has changed,but SHEI,SHDI,PD,DIVISION,and PSCV are still highly effective in the evaluation of the LID runoff control effect Therefore,the rain peak coefficient and rainfall duration affect the evaluation ability of SHEI,SHDI,PD,DIVISION,and PSCV to a lesser degree,without affecting the effectiveness of the evaluation ability.At the same time,the significance of the correlation between the landscape index and the peak flow reduction rate shows instability with changes in the rain peak coefficient and rainfall duration,mainly affected by the recurrence period.Except for the unstable PSCV evaluation ability of submerged green spaces,other landscape indexes have higher evaluation ability.(5)The LID hydrological process evaluation index includes three indexes,LID spatial infiltration contrast index(LSICI),LID spatial storage contrast index(LSSCI),and LID spatial function contrast index(LSFCI),which have good evaluation significance and can be used to predict the site LID landscape type runoff control and peak flow reduction effect.LSICI was significantly negatively correlated with field rainfall runoff control rate and peak flow reduction rate,and LSSCI and LSFCI were significantly positively correlated with field rainfall runoff control rate and peak flow reduction rate,indicating that LSICI,LSSCI and LSFCI were effective in evaluating runoff control effect and peak flow The reduction effect is consistent and is not affected by the size of the study area.(6)Different rainfall durations and different peak-to-peak coefficients will have a certain degree of influence on the significance levels of LSICI,LSSCI,LSFCI and field runoff control rate and peak flow reduction rate.The capacity of the flow reduction effect,that is,the duration of rain and the coefficient of the rain peak does not affect the accuracy of LSICI,LSSCI,and LSFCI.(7)On the basis of the traditional landscape index,the LID landscape spatial function comparison index is superimposed to form SHDI-LSFCI,SHEI-LSFCI,PD-LSFCI,LPI-LSFCI,DIVISION-LSFCI,PSCV-LSFCI,the combination of the two enlarges the new comprehensive The landscape index evaluates the ability of the LID landscape type to control runoff and reduce the peak flow process,which is consistent with the actual function of the LID landscape type.By comparing with the traditional landscape index,the integrated landscape index has a good evaluation in different scenarios.Significance and consistency of evaluation results.