1. LiDAR to optimize local
government investigations
Sera Lambe
Investigations Officer
Tableland Regional Council
2. Experience
• Civil Works Construction
– Earthmoving
– Excavation project marking
• Studied Spatial Information Systems
– Survey component does not mean it is a
survey course.
• Council contract in Investigations
3. Drainage Improvement Requests
• Establish procedures
• Investigate
• Preliminary design of potential solution
• Estimates of quantities and costing
• Reports for consideration at Council
• List the project to be prioritized for funding
4. LiDAR
• Minimizes in the field investigations time
reducing costs for mobilization
• More efficient use of time
• Minimizes the resources needed in the
preliminary design stages.
• Provides a huge amount of available data
for further investigation
5.
6. Rainfall Events
What to consider when designing
stormwater infrastructure
• Intensity, the rate at which rainfall occurs
• Frequency, how often a storm is likely to
occur
• Duration, how long the storm lasts
10. Sedimentation and Erosion
• Changes within
drainage infrastructure
– Quantity of materials
deposited or lost
• Changes in flow paths
• Vegetation within
drainage easements
– Conveyance of
properties
20. LiDAR
Potential Uses
•Preliminary design of infrastructure to manage stormwater
•Preliminary designs of new housing developments
•Stormwater infrastructure management
•Quantity and Estimates for costing projects
•Change detection within stormwater infrastructure
•Documenting site specific information
•Identifying flow paths and the minimum design requirements for
properties lower down the catchment
Editor's Notes
Hi I'm Sera I'm working as an Investigations Officer at the Tableland Regional. I will discuss, how I use LiDAR and the potential I see for this resource within local government. The Tableland Regional Council is a geographically diverse region which is larger than the land mass of Tasmania. It covers a broad range of vegetation types including rainforests to dry arid areas. North Queensland is known for its monsoonal wet season. Flash flooding and cyclones are characteristics of this region. As an Investigations Officer for the Tableland Regional Council, drainage related problems are a significant portion of the issues I deal with.
I know I probably don’t look like your stereotypical truck driver but my history is with Civil Construction as a machinery operator driving excavators, loaders, screening plant and bobcats etc. My computer skills at this point were lets say basic. I worked fixing peoples driveways and constructing house pads, I think a large percentage of my customers just enjoyed watching a girl drive big toys. The job was fantastic, out doors, heaps of fun and it didn’t really require a lot of grey matter. I started looking into survey and took levels for basic surveys of construction sites. I decided survey would be a practical way to advance in the construction industry so I enrolled to study Spatial Information thinking its main component would be survey. What I didn’t realise was that this course was based around Geographic Information Systems. I decided pretty quickly that I wanted some practical experience and approached AtGIS the council GIS team for some work experience. I was then offered work within Council as a contractor for 9 months within the Civil Works Investigations Team. I was given access to a large dataset of LiDAR las files and 12.5cm imagery and asked to demonstrate how this resource could be used to report on Council related infrastructure, including drainage improvements, mining lease applications, gates and grids etc. I have now accepted a full time position with further university studies in spatial science.
As a Council Investigation Officer my role is to Investigate and gather information relevant to a number of key issues under Civil Works area of responsibility. The main areas I wish to talk to you about today is drainage. Council has in place drainage infrastructure to manage stormwater and erosion and limit property flooding and the degradation of downstream environmental values. For each drainage request that I receive I have: Establish procedures for mapping and analysis of drainage related issues. I.e flow paths, flow accumulation identification of catchments as any works within a catchment will cause changes effecting down stream areas. I Investigate the issue and collect any relevant data and photos of the problem from the site. I come up with preliminary designs for the potential solution to these drainage issues. I estimate quantities of things like sediment build up and erosion and estimate materials needed to carry out projects to fix the problems. My findings are documented and are reported to Council in order to gain funding.
From this position within Council I can see that there is the potential to use LiDAR to extract a wealth of relevant information. A few pros for the utilization of this data include cutting the associated costs by limiting the need for resources. Resources including mobilization of council personnel to specific sites – this would include wages ,vehicle fuel equipment etc When you think that the TRC is the size of tasmainia and that within my team I have 3 members and at any one time 300 odd tasks to investigate, time saving is a huge benefit. More site specific information would be on hand to determine significant contributing factors to the issue prior to onsite inspection and therefore if a site inspection became necessary more attention would be made to specific details. From the LiDAR dataset a huge resource of information is available to determine quantities, distances and estimates where the neccessity for survey accurate detail is not required. The need to revisit a site to gather data and information that either wasn’t collected the first time or wasn’t thought about becomes obsolete in the preliminary stages as I can look into the site from my desktop. This may not always be a plus because I actually really enjoy the field work.
This is a pretty good indication of the type of weather conditions tropical far north queensland experiences
Drainage infrastructure is designed to cope with stormwater events These designs are categorized according to the type of events it is likely to experience such as 1 in 100 year event or a 1 in 5 year event. These specifications refer to the severity of flooding and timeframe for which floodwaters are present. When events such as cyclone Larry of 2008 took place infrastructure is designed to minimize flooding to properties though this is not always the result as you will see in the next slide. During cyclone events, areas of the region are inundated with flash flooding that take many days to subside. Poor designs will quickly become apparent in these situations. One of the biggest problems I come across are things like easements which are basically an earthen stormwater spoon drain. Some places have these easements in place which run down hill then because of the shape of a property suddenly make a 90 degree turn. Somebody simply forgot to tell the water to make a 90 degree turn when naturally it just wants to go down hill. This next slide demonstrates how design effects stormwater management.
Even though the waterfall in the back yard is quite pretty this property owner was not too impressed by the flooding to his property and damages to his driveway. This film was recorded by the owner of the property during a pretty ordinary rain event in Atherton. Storm water is collected and channeled down to the back of his property by the kerb and guttering on the road behind his house. Water flowing down hill was channeled by the road. Once it came to the intersection it just kept flowing downhill and this property owner soon realized his house is at a low point in the catchment. I did edit out a few of his choicest words here. (after movie finished) A large diversion mound was constructed to direct water to a large allotment were it would not effect property owners. When coming up with potential solutions it is nesseccary to consider changes made in the flow path and where new problems may arise.
A bare earth model showing the property owners house and the road at the back of his property which is channelling water into his yard. the kerb is not only collecting overland flows but acts as a catchment directing water from all blocks to the road side. No body wants stormwater on their properties so people and councils try to get the water away as quickly as possible. This attitude increases the volumes of water and the velocity at which it travels.
So this example identifies the types of drainage and storm water events found within the TRC LiDAR has the potential to deliver some pretty relevant data with relation to these issues. The example of a drainage easement in this photo show a build up of sediment. LiDAR could potentially be used to identify easements in need of maintenance. There are numerous different types of drainage infrastructure including easements. Easements are parcels of land maintained by council which gives storm water a path through properties. Velocity of this storm water causes erosion and carries within the stormwater a large amount of sediment which is then deposited further downstream and contributes to a number of these systems to become unable to function at capacity. Management of these can create an ongoing need for maintenance which means funding to insure the designed integrity of these structures. As constructed drawings provide information on the type of design and constructed infrastructure to deal with stormwater.
LiDAR could be used to create a maintenance schedule of councils infrastructure to determine weather vegetation, sedimentation and or erosion have become a problem. Sedimentation and erosion begin when the velocity of water becomes so great that the system is unable to cope. The drain becomes eroded as seen in this photo. Sedimentation and erosion can cause changes within a system within one wet season. A large amount of sediment can be scoured away. These changes can be detected in the LiDAR
Flow accumulation where likely flow paths are in relation to drainage easements.
These as constructed drawings contain the deigned specifications and locations of the installed infrastructure. After a number of years a designed drainage easement can become so full of sediment that the flow of water can be changed and channeled causing large volumes of water to be discharge to unintended properties. These kind of changes were usually only detected once a rain event happened and properties became flooded. With the use of LiDAR easements could be investigated to determined if significant changes have occurred over a period of time. Again this would reduce the need for physical site insepections as a routine maintenance schedule could be carried out using LiDAR to assess the condition of infrastructure
As constructed drawings give precise details of infrastructure Note there in a 450mm rcp it gives its length. I refer to a investigation I carried out on this easement. Water was flooding the property to the right. The kerb inlet was unable to take enough water into the pit to be pied away. Further investigation revealed that the pipe had been extended thus decreasing the amount a stormwater able to be received by the pipe. I was able to locate the pipe outlet in the LiDAR and imagery.
Localized drainage reports gives exact dimensions for the infrastructure
Dimensions , batter slope ratio , design flows and location information are all at hand with as constructed drawings
From this representation of the LiDAR point cloud it is easy to identify vegetation within the drainage easement. Not only have these easements had trees planted but it can also be identified that a fence line is well over the easement boundary. These contribute to the reduction in the drainage capacity.
Cross section extracted from point cloud information.
Cross sections are a relatively easy way to demonstrate the capacity of drainage easements. These cross sections show an easement that is full of sediment and the changes that has made as to where storm water will now flow.
Identification of flow paths to go with the natural flow of stormwater runoff.
