Performance Evaluation of Low Impact Development Practices Using Linear Regression

Aims: To develop a modelling methodology for evaluating the cumulative stormwater performance of Low Impact Development technologies on a watershed basis to address stormwater impacts of urban development.
Study Design: A method is presented to perform hydrological modelling on large watersheds. Hydrological modelling simulations and linear regression analyses of a small sample of randomly selected lots were performed to generate results which were extrapolated to the entire watershed.
Place and Duration of Study: Department of Civil Engineering, Ryerson University, between September 2010 and September 2012.
Methodology: Urban hydrological response units were developed by using the K-means cluster analysis procedure to group 6926 lot parcels amenable to the residential rain barrel Low Impact Development practice into clusters. Two versions of a Microsoft Excel macro were developed to run simulations for thousands of lots simultaneously before and after Low Impact Development implementation to determine the total runoff produced by all lots for both cases. The results of computer modelling all lots were compared with the results from developing calculation methods to be used after computer modelling subsets of lots. Two calculation methods based on clustering lots to form urban hydrological response units were developed.
A random sample of 5 % of all lots was then extracted from 6616 lots amenable to the porous pavement Low Impact Development. Stepwise linear regression and linear regression were performed on the random sample for each case of no Low Impact Development and with Low Impact Development. Regression equations were used to extrapolate results from the sample to the entire data set to determine the total runoff volume produced by each set of lots.
Results: Results from the cluster-based calculation methods developed as applied to residential rain barrels were unsatisfactory since they did not approximate the output values from modelling all lots using software. The alternative method applied to porous pavement Low Impact Development implementation, entailing stepwise linear regression and linear regression, produced 945,382.97 m3 and 747,380.13 m3 of total runoff respectively. These values closely approximated corresponding values generated by the modelling software of 937,088.58 m3 and 746,462.40 m3.
Conclusion: The formation of urban hydrological response units may be unnecessary for hydrological modelling Low Impact Development technologies for large watersheds. Hydrological characteristics for only a small, randomly selected subset of all lots can be used to determine total runoff volume produced by all lots in the watershed before and after Low Impact Development implementation.