Project Title: The Hydraulic Resistance and Stability of Vegetation in Swale 

Funder: RU Grant


Duration: October 2009 - October 2012





Grassed swales refer to a series of vegetated, open channel practices that are designed specifically to treat and attenuate stormwater runoff for a specified water quantity volume.It specify as beneficial alternatives to concrete gutters for stormwater management due to their advantages of infiltration and filtration of stormwater. As stormwater runoff flows through the channels, it is treated through filtering by the vegetation in the channel, filtering through a subsoil matrix, and/or infiltration into the underlying soils.


There are many design variations of the grassed swale, including the grassed channel, dry swale and wet swale. The specific design features and treatment methods differ in each design, but all are improvements on the traditional drainage ditch. Each incorporate modified geometry and other design features to use the swale to treat and convey stormwater runoff.


Grassed swale in Engineering Campus, Universiti Sains Malaysia (USM) is a part of the pilot project of Bio-Ecological Drainage System (BIOECODS) which include of perimeter swale and ecological swale. This research study will focusing in the implementation of the Best Management Practice (BMPs) in a drainage system especially on constructed grass swales. Six locations (Figure 1-6) of the constructed swale as illustrated in figures below, will be used as a field study area.



Figure 1 : Clinic (Site 1)


Figure 2 :  Chemistry School (Site 2)


Figure 3:  Civil  School (Site 3)


Figure 4 : Aerospace  School (Site 4)


Figure 5 : Mechanical School (Site 5)


Figure 6: USM Hall (Site 6)


There are 2 types of ecological swale that includes in this study which are :


i .Ecological Swale - Type A

Cross Section of Swale - Type A


Swale Type A in Dry Period


Swale Type A in Wet Period


ii. Ecological Swale -Type B

Cross Section of Swale -Type B


Swale Type B in Dry Period


Swale Type B in Wet Period


There are several methods for determining Manning n in vegetated channels. These methods recognize that the physical characteristics and growth patterns of vegetation are important factors in evaluating hydraulic resistance. The objective of the study is to develop a set of equations to calculate the hydraulic resistance and to determine the stability of vegetation in swale channel. To achieve these objectives, the field study through these six location, concerning stage-discharge, flow resistance, bed forms and flow structures will carried out in a vegetated grass swale channel.


This study is also to investigate how density and arrangements of vegetation influence stage-discharge, flow resistance, bed forms and flow behaviours. The collected data such as rainfall, flow, depth of flow, slope, grass type, length of swale and sampling time from October 2009 until 2011 will analysed and tested. Methods and procedures will developed using three mowing type of grass height to quantify both geometric and biomechanical properties of the plants when determining the vegetation resistance. A new set of equations will provide a basis by which to quantify hydraulic resistance and stability of vegetation in swale.