QUANTIFYING THE POTENTIAL FOR A LOW-COST, DISTRIBUTED
STORMWATER DETENTION SYSTEM USING LIDAR AND REMOTELY SENSED
DATA
Integrating Science Theme
Subtheme 4a: Understanding current and future resource conditions through analysis of
remote sensing data
Principal Investigator: Dr S. Geoffrey Schladow
University of California, Tahoe Environmental Research Center
One Shields Ave, Davis CA 95616
Ph (530) 752 3942; Fax (530) 754 9364; gschladow@ucdavis.edu
Co-Principal Investigators: Dr Juanfran Reinoso and Dr Carlos Leon
Department of Graphic Expression in Architecture and Engineering
University of Granada, Spain
jreinoso@ugr.es
cleon@ugr.es
Agency Contacts:
Shane Romsos
Hannah Schembri
Jason Kuchnicki
Dave Roberts
Mahmood Azad
Russ Wigart
TRPA
Lahontan
NDEP
TRCD
NTCD
El Dorado County
Grants Contact Person:
Kendra Smith
Office of Research/Sponsored Programs
1850 Research Park Drive, Ste 300
Davis, CA 95618
Phone: 530 754-8224; FAX: 530 754 8229; kosmith@ad3.ucdavis.edu
Total Funding Requested: $123,602
Total Cost Share:
II. Proposal Narrative
a. Project abstract
The input of fine sediment particles (and associated nutrients) to Lake Tahoe has been identified
as a major cause of clarity decline over the last 40 years (Roberts and Reuter 2007). Efforts to
reduce fine sediment inputs, particularly from the highly contributing urbanized areas adjacent to
the lake, are the main focus of the recently signed TMDL for Lake Tahoe. This project seeks to
utilize newly acquired LiDAR data and other remotely sensed data to identify and quantify the
potential to develop stormwater detention and infiltration areas based on small-scale patterns of
land topography. Utilizing the high vertical accuracy and resolution inherent in the existing
LiDAR data set, it is feasible for the first time to identify the hydrologic connectivity and the
topographic features of the urban areas and the wildland-urban interface (WUI) areas in the
entire Tahoe basin. Based on this information it is now possible to identify the volume of Micro
Stormwater Infiltration Systems (MSIS) achievable by small modifications to existing culverts,
construction of small retaining walls, and in relatively simple ways utilizing the features of the
existing topography. Remotely sensed data and current GIS layers will show whether these MSIS
areas intrude on private property, existing infrastructure, sensitive lands etc. The project will (1)
quantify the volume of stormwater detention available through this means; (2) test the
methodology on an existing urban area in collaboration with a local agency; (3) rank the
individual MSIS by volume (largest to smallest) within each basin watershed; (4) working with
local jurisdictions assign a water quality weighting to each of the volume-ranked MSIS that
indicate the highest influx of fine sediment particles; (5) develop a methodology whereby the
accumulated sediment in an MSIS can be sampled, analyzed for particle size distribution and
thereby provide firm data for the assignment of TMDL credits and validation of existing
crediting tools (such as the Pollutant Load Reduction Model PLRM); and (6) make available a
design tool utilizing TERC’s existing 3-D visualization laboratory where agencies can easily
view and design these MSIS in an immersive three dimensional environment using the LiDAR
data and other spatial data.
b. Relationship between the proposal and the sub-theme
This sub-theme is directed at the utilization of the LiDAR and remote sensing data sets that were
acquired through the Round 10 SNPLMA capital program, and to develop information that can
be used by agencies in future planning of capital projects. This proposal meets that goal. It is
based on the use of both the LiDAR and the WorldView2 datasets, as well as using other GIS
layers that have been developed by the agencies over many years (for example, NRCS soil maps,
vegetation maps etc.). In addition the project will utilize products currently being derived from
the LiDAR data set under Round 11 SNPLMA Research funding, specifically the impervious
surface map being developed by the Spatial Informatics Group and the University of Vermont
(O’Neill-Dunne, personal communication). With the products and tools developed under this
proposal, agencies will have an ability to consider a broad range of stormwater management
options that can be located at the most critical locations taking into account current and future
2 land uses. In addition, it is based on the assumption that there is a significant area of land
available for stormwater treatment on small parcel and sub-parcel spatial scales, and that land on
these scale would not normally be considered for conventional stormwater treatment projects
(e.g. basins, large meadow infiltration, wetlands). It speaks directly to Objective 2c, “map
hydrologic networks to inform fine sediment and nutrient pollutant load reduction project
planning and/or floodplain management”. It actually goes further than this in that the project not
only maps the hydrologic network (i.e. connectivity) it uses this information combined with
topographic information to provide agencies with a set of ranked, potential project locations and
sizes that they can choose between to meet specific sediment and nutrient reduction goals in the
context of the prevailing economic climate.
c. Concise background and problem statement
Under natural conditions stormwater can infiltrate into the soil, a process which sequesters fine
particles, nutrients, heavy metals etc. In urban areas, which are typically dominated by
impervious surfaces such as concrete and asphalt, stormwater cannot infiltrate (Roy & Shuster,
2009). On the contrary stormwater travels at higher velocity over such surfaces giving it the
potential to accumulate more contaminants from the surface and to cause accelerated erosion if it
traverses natural or disturbed soils downstream. Treating stormwater generally entails expensive
water treatment processes, similar to domestic wastewater. More often it flows directly and
untreated into receiving water bodies such as streams, lakes or coastal zones.
The input of fine sediment particles (and associated nutrients) to Lake Tahoe has been identified
as a major cause of clarity decline over the last 40 years, with over 70% of those particles
coming from urban areas (Roberts and Reuter 2007). Efforts to reduce fine sediment inputs,
particularly via stormwater from the highly contributing urbanized areas adjacent to the lake, are
the main focus of the recently signed TMDL for Lake Tahoe. There are currently many efforts
underway to identify opportunities to construct stormwater treatment or detention/infiltration
projects to address this pressing need. What characterizes many of these projects is their large
scale, and their associated high costs both in terms of the planning and permitting, and in terms
of construction and maintenance. Until recently there was an assured source of funding for many
large projects through the Southern Nevada Public Lands Management Act (SNPLMA) as
authorized through the federal Lake Tahoe Restoration Act. However, with the end of both the
funding and the authorizing legislation in sight, combined with the prevailing economic
conditions in the states of California and Nevada and locally in the Lake Tahoe basin, it is
questionable how many of these projects can be constructed in the coming years. At the same
time there is the imperative presented by the TMDL (as authorized under the federal Clean
Water Act) for measurable progress toward reduction of sediment and nutrient loads to the lake,
and the improvement of lake clarity.
This project seeks to identify and quantify the full range of small, spatially distributed
stormwater detention/infiltration opportunities available in the urban areas and the wildland
3 urban interface (WUI) areas of the Tahoe basin. The types of opportunities we are focusing on
have the following advantages:
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sufficiently small that they are subject to the minimum amount of permitting and
planning requirements,
location is closer to the stormwater runoff source,
utilize the existing infrastructure to a larger extent,
expected to have low construction and maintenance costs because of their small size,
overcome the issue of having insufficient flat land available for large detention basins or
treatment wetlands, and
should have minimal influence on the ecology of native fauna since the areas are already
small.
The expectation is that in aggregate there are a sufficient number of such sites that they have the
potential to significantly reduce the total amount of untreated stormwater that drains directly to
the lake. The quantification of this last statement (i.e. the fraction of the total urban stormwater
that can be captured and treated in this way) is a major task of the present proposal.
d. Goals, objectives, and hypotheses to be tested
The primary goal of this project is to utilize recently acquired LiDAR data and other remotely
sensed data to identify and quantify the potential for small-scale stormwater distribution systems
in the Tahoe Basin. Utilizing the high vertical accuracy and resolution inherent in the existing
LiDAR data set, it is feasible for the first time to micro-scale topographic features of the urban
areas and the WUI areas around the entire Tahoe basin. We will analyze the potential of small
depressions in the natural landscape to be utilized to provide detention areas for fine scales
particles in order to reduce the quantity of fine sediment and nutrient pollutant that reach Lake
Tahoe. These Micro Stormwater Infiltration Systems (MSIS) have many advantages for Lake
Tahoe. Part of this goal is to find solutions that require only minimal engineering changes. The
corresponding hypothesis is that the available LiDAR data can be used to identify the volume of
potential stormwater storage achievable by small modifications to existing culverts, construction
of small retaining walls, and in general utilizing the features of the existing topography.
The other goal is to understand and map the fine scale hydraulic connectivity in the urban
watershed so that projects can be designed efficiently (i.e. without multiple basins “treating” the
same water multiple times) and that a balance can be sought between retaining water on the
landscape and avoiding under flooding and inundation. The corresponding hypothesis is that the
existing Worldview2 data and other existing GIS data will allow for the MSIS to be designed
without negatively impacting existing infrastructure.
The objectives of the project are to:
(1) Quantify the volume of MSIS available through these small-scale features. and compare it to
the overall stormwater detention required to achieve the TMDL goals. Other remotely sensed
4 data (e.g. WorldView 2) and current GIS layers will show whether these potential stormwater
detention areas intrude on private property, existing infrastructure, sensitive lands etc.;
(2) Test the methodology on a specific project area where it is ready to be utilized (this will
likely be the Montgomery Estates Phase 2 project in collaboration with the Tahoe Resource
Conservation District as part of a SNPLMA Round 12 capital project);)
(3) Rank the individual MSIS by volume (largest to smallest) within each basin watershed
(4) Work with local jurisdictions to assign a water quality weighting to each of the volumeranked MSIS that indicate the highest influx of fine sediment particles based on a combination of
factors such as upstream land use, soil type and slope
(5) Develop a simple methodology whereby the accumulated sediment in such small scale
detention basins can be sampled, analyzed for particle size distribution from a known
contributing area and thereby provide firm data for the assignment of TMDL credits and
validation of existing crediting tools (such as PLRM). Because of the spatial distribution and the
potentially large number of sites, this data will be far more valuable than measurements at one or
two large facilities, and
(6) Make available a design tool utilizing TERC’s existing 3-D visualization laboratory where
agencies can view and design these detention basins in an immersive three-dimensional
environment using the LiDAR data and other spatial data. Software tools to enable agency staff
to conduct their own analyses are currently being developed under separate National Science
Foundation funding.
e. Approach, methodology and location of research
The approach is based on using the existing Airborne Light Detection and Ranging (LiDAR)
data set for the Tahoe basin. These data offer the potential of providing extremely high resolution
and high accuracy (at the centimeter scale) topography, as well as discerning areas of impervious
(higher reflectivity) and natural (lower reflectivity) surfaces. LiDAR data have been used to
determine high accuracy hydrologic networks (Murphy et al., 2008, Liu and Zhang, 2010). This
research aims to develop a new technique for treating urban storm water by making use of
LiDAR data. In essence it will quantify the potential for Micro Stormwater Infiltration systems
(MSIS) by calculating the volume available for water storage upstream of existing road culverts
and natural depressions. With minor engineering changes it will be possible to utilize this storage
volume to allow for infiltration without increasing flooding potential.
Watershed Sciences, Inc. (WSI) collected airborne Light Detection and Ranging (LiDAR) data
of land surrounding Lake Tahoe from August 11th to August 24th, 2010. The area of interest
excluding the actual lake, resulting in 232,536 acres of delivered LiDAR data. The resolution
demands on the survey were such that a very high resolution and high accuracy product resulted,
with an average of 11.82 points/m2 and a vertical accuracy (1σ) of 3.5 cm (Watershed Sciences
5 2011). The project will focus on those areas of the basin considered to be either urban areas or
the urban wildland interface. This represents approximately 20% of the land area in the basin.
One DEM product delivered by WSI as part of the LiDAR data acquisition was a
“hydrologically-enforced bare-earth surface model”. The most notable features are the following:
a) the hydrologic model has a DEM format, b) Hydro-enforcement enables hydrologic and
hydraulic models to depict water flowing under the structures (bridges and culverts), rather than
appearing to be dammed by them because of road deck elevations higher than the water levels,
and c) the cell size is 0.5 m (Watershed Sciences 2011). Our proposal builds on the use of this
previously conducted work. In addition, we will be working directly with the LiDAR point cloud
itself and bypassing the need to create the DEM. Software developed at UC Davis
(LiDARViewer-2.5) provides an opportunity for the user to view point cloud datasets without
sub-sampling or reducing the data. The program will load in a point cloud and display each
individual point from the survey. LiDARViewer-2.5 allows the user to select points and extract
them to a separate file, extract primitives (plane, sphere, cylinder) from selected points,
determine distance from a plane, and navigate in real-time through large datasets (>2.7 billion
points). It is a powerful tool that can provide unique perspectives to LiDAR datasets that are
difficult to attain through DEMs.
To test the potential for MSIS several steps are required. First, the existing stormwater flow
patterns need to be determined using the LiDAR data. The available resolution and the nature of
LiDAR will allow for the highly complex, dendritic structure to be revealed (even under existing
vegetation). Second, the existing road and culvert network need to be overlaid on this (this is
currently being performed under a separate SNPLMA Round 11 project). Third, the volume of
available water storage behind each culvert and natural depression needs to be evaluated. This
has to be done taking into account the adjacent roadway elevation and adjacent property so that
flooding of roads and developed property is prevented. The methodology used for achieving the
objective is based in the identification of Candidate Areas (CA) to retain the greatest quantity of
water coming from urban areas. Our methodology follows the workflow shown in Figure 1.
e.1. Determining Global Hydrologic Network
Working with the entire hydrologic network with a cell size of 0.5 m requires large computation
resources. To reduce the computation effort we will sub-divide the whole Lake Tahoe watershed
into sub-basins and process them independently using a down-scaled cell size of 30 m from the
LiDAR dataset. The downscaling will be carried out using multi-resolution techniques that have
high shape conservation of the original DEM when a resolution reduction is performed (Reinoso
2010). This network is necessary in order to initially identify the intersections of drainage
pathways with urban and road areas and to act as a guide for the more detailed analysis.
e.2. Determining Local Hydrologic Network
For each sub-basin a Local Hydrologic Network will be computed using the full 0.5 m LiDAR
DEM. Using this high resolution network it is possible to focus on micro-scale topography and
lower order streams (Liu and Zhang, 2010), and the details of their intersection with crossing
6 urban lots or road areas. An estimation of the horizontal error between the 30 m Global
Hydrological Network and the 0.5 m Local Hydrological Network can be carried out using the
algorithm of Reinoso (2011). An example of the use of this algorithm is shown in Figure 2,
where the mismatch between contours generated form the Global and Local networks are evident
in the right hand panel. The spacing between the two contour lines is an indication of the error.
e.3. Identifying Candidate Areas (CA)
With the Hydrologic Local Network we will use two primary methods to detect the candidate
areas (CA) from which to refine choices for MSIS. These methods are:
- Point cloud grading. Each point from the LiDAR point cloud is assigned a color. This method
facilitates rapid detection of CA's in a highly graphical fashion (Figure 3).
- LiDARViewer. This is public domain software developed by the UC Davis KeckCAVES, for
analyzing LiDAR data in a three-dimensional immersive environment (Kreylos et al. 2008). This
project will primarily use the available LidarViewer tools for the identification of CAs. The use
of immersive 3-D displays is included in the project budget.
e.4. Modify Candidate Areas
Using GIS overlays (impervious surfaces, property lines, stream environmental zones etc.) the
identified CAs will be modified to avoid interference. For example in Figure 4, two Candidate
Areas have been identified where, through the construction of two low retaining structures,
almost 900 m3 of detention volume can be created that take advantage of natural depressions in
the hill side downstream from an urban area. Once precise property lines are overlain, it may be
necessary to modify these CAs in order to meet the land owners wishes or address other sitespecific concerns.
e.5. Ground truthing
In order to increase confidence that the CAs identified through analysis of the LiDAR data do
indeed agree with on-the-ground conditions, a limited number of ground truthing exercises will
be conducted. These will comprise of site visits to several of the most highly ranked MSIS sites
with the local agencies that are most likely to construct these facilities in the future.
f. Relationship of the research to previous and current efforts
This project builds directly upon LiDAR data gathered by the basin agencies, through SNPLMA
funding, for precisely this type of purpose. It utilizes ongoing research (identification of
impervious surfaces) to avoid duplicating effort, and the work is targeted at what has been
determined to be the most pressing environmental improvement issue facing local agencies –
finding economical and effective ways to reduce movement of fine sediment and nutrients to
Lake Tahoe. With the signing of the TMDL by the states of California and Nevada in August
2011, basin regulatory agencies and the local jurisdictions have now entered the phase of
undertaking projects that will reduce fine sediment and nutrient inputs to the lake. This research
is directed at assisting that effort. The results of this investigation will be useful to the Tahoe
Regional Planning Agency as it develops projects and implements the Environmental
7 Improvement Plan to meet TMDL load reduction targets. It will also help the California Tahoe
Conservancy, Nevada Division of State Lands and the US Forest Service as owners of some
multi-purpose yet small parcels to best management these properties. Local governments have
received load reduction requirements as part of the newly approved Lake Tahoe TMDL. The
results from this study will allow them to better identify cost-effective pollutant reduction
opportunities within their jurisdictions.
g. Strategy for engaging with managers and obtaining permits
No permits are required for the proposed work as it is all computer-based.
Numerous agencies have already been briefed on the nature of the proposed work and they fully
appreciate the potential and need for the project. During the conduct of the project, managers
will be engaged in several ways. First, at an initial meeting mangers will be asked to identify
areas of special interest that may be used as future proofs of concept or for ground truthing
exercises. Second, at about the midpoint of the project, the expertise of the agency staff will be
used to identify the water quality rankings of identified MSIS opportunities. This will take the
form of a one-day workshop. Third, during ground truthing, we will work with agency staff.
Fourth, near the conclusion of the project we will run a training session to show agency staff how
to use LiDARViewer as part of their own use of the LiDAR data and for the design and
refinement of MSIS projects.
h. Description of deliverables
For each watershed, a ranked list of MSIS opportunities will be produced (including surface area,
volume, depth, watershed area served, GPS location) and included as part of the final report
Sets of maps showing the locations of MSIS and the hydrologic connectivity of the basin, will be
produced and made available to end users through either the TERC website or TIIMS.
A simple methodology for agencies to take core samples of accumulated sediments in an MSIS
in future years and relate the measured capture of fine particles to the drainage area served will
be developed.
A workshop in which agency representatives will be instructed in how to use the LIDARViewer
as part of future project designs will be conducted.
Results of the project will be presented at the biannual Tahoe Research Symposium as well as
meetings of professional societies. We anticipate that 1-2 peer-reviewed papers will be produced
from this effort.
The LiDAR data that are used to construct this will be housed at TERC, and agency staff will be
free to utilize TERC’s 3-D facilities to analyze data in the future.
8 III. Schedule of major milestones/deliverables in a table with estimated start and end dates
(include quarterly progress reports and annual reports)
Jul-12
Oct-12
Jan-13
Apr-13
Jul-13
Sep-13
Kickoff meeting
Mid-point
workshop
Agency training
Initial list of CA
Final List MSIS
MSIS map
Connectivity Map
Quarterly Report
Annual Report
Final Report
9 IV Literature Cited
Kreylos, O., Bawden, G.W., and Kellogg, L.H., Immersive Visualization and Analysis of LiDAR
Data, in: Bebis, G., et al., "ISVC 2008, Part I," LNCS 5358, Springer-Verlag Berlin Heidelberg,
pp. 846-85
Liu, X., Zhang, Z., 2010. Drainage network extraction using LiDAR-derived DEM in volcanic
plains. Area. 43(1): 42-52.
Murphy, P., Ogilvie, J., Meng, F. and Arp, P., 2008. Stream network modeling using LiDAR and
photogrammetric digital elevation models: a comparison and field verification. Hydrological
Processes. 22: 1747-1754.
Reinoso, J. F., 2010. A priori horizontal displacement (HD) estimation of hydrological features
when versioned DEMs are used. Journal of Hydrology. 384: 130-141.
Reinoso, J. F., 2011. An algorithm for automatically computing the horizontal shift between
homologous contours from DTMs. ISPRS International Journal of Photogrammetry and Remote
Sensing. 66: 272-286.
Roberts, D.M. and Reuter, J.E. 2007. Lake Tahoe Total Maximum Daily Load Technical Report.
Produced on behalf of the Lahontan Regional Water Quality Control Board and the Nevada
Division of Environmental Protection. 341 p.
Roy, A. H. and Shuster, W. D., 2009. Assessing impervious surface connectivity and
applications for watershed management. Journal of the American Water Resources Association.
45(1): 198-209.
Watershed Sciences 2011. LiDAR Remote Sensing: Lake Tahoe Watershed, CA-NV. Report to
the Tahoe Regional Planning Agency, January 31, 2011. 41p.
10 V. Figures
Figure 1. Proposed workflow.
11 Figure 2. An example of the mismatch in contours produced by using a 30 m DEM and a 0.5 m
DEM. Contours from both DEMs are overlaid, so the thickness of the separation is an indication
of the error.
12 Figure 3. Color coded point cloud data. The upper panel shows a portion of the south east of the
Lake Tahoe basin, with two candidate areas (CA) indicated. The lower panel shows an
enlargement of the two CAs that are formed by depressions in the topography.
13 Figure 4. An example of two potential candidate areas for MSIS. With the construction of low
embankments (maximum height 1m and 1.5 m respectively) almost 900 m3 of
detention/infiltration volume is produced.
14