tools to quantify urban stormwater load reduction … seabright ave, suite 205 santa cruz,...

500 Seabright Ave, Suite 205Santa Cruz, California 95062p 831.426.9119 f 831.426.7092 w 2ndnaturellc.com

Tools to quantify urban stormwater load reduction from SEZ restoration actionsSNPLMA Research Proposal: Round 11 Theme 2C. Quantifying the effects of actions to reduce sediment loads using Stream Environment Zones (SEZs)

Principal Investigator: Nicole Beck, PhD, 2NDNATURE LLC, [email protected] 500 Seabright Ave, Suite 205 Santa Cruz CA 95062 Tel: 831.426.9119 Fax: 831.426.7092

Research Collaborators: Catherine Rihimaki, Drew University, [email protected] Jeremy Sokulsky, Environmental Incentives [email protected]

Grant Contact: Krista McDonald, 2NDNATURE LLC, [email protected], p 831.426.9119 Total Funding Requested: $150,000.00

Proposal: Tahoe Research Supported by SNPLMA Round 11 p. 1 Theme 2c: Quantifying the effects of actions to reduce sediment loads using Stream Environment Zones (SEZs)

2NDNATURE, LLC 500 Seabright Avenue Suite 205 Santa Cruz CA 95062 p 831.426.9119 w 2ndnaturellc.com

II. Proposal Narrative

A. ABSTRACT

This research will provide a recommended estimation approach for managers of the potential load reductions from two types of stream environment zone (SEZ) improvements: 1) improving floodplain connectivity through stream restoration of perennial systems, and 2) increasing the function of SEZs that receive direct urban stormwater to retain water and intercept pollutants before entering perennial streams. The recommendation will include methods to estimate the hydrology and expected fine sediment loading for any scale of SEZ and identify critical site specific geomorphic and vegetation attributes necessary to complete such estimates. The methodology will include data from specific stream and SEZ test sites, and used to inform a methodology to provide researchers and stormwater engineers with a consistent and relatively accurate method to estimate the pollutant load reductions from specific SEZ improvement projects. This research builds on existing models, datasets and past and ongoing SNPLMA‐funded efforts by the 2NDNATURE team, leverages existing datasets, methods and models in a manner consistent with the TMDL Pollutant Reduction Opportunity analysis (LRWQCB and NDEP 2008), and is directly applicable to the Lake Clarity Crediting Program (LRWQCB and NDEP 2009).

B. JUSTIFICATION STATEMENT

Resource managers need tools to quantify the water quality benefits of SEZ restoration efforts in a manner comparable and consistent with the stormwater quality load reduction tools that have been developed to support the Lake Tahoe TMDL (LRWQCB and NDEP 2010) and Crediting Program (LRWQCB and NDEP 2009). It is assumed that SEZ restorations may result in substantial removal of urban pollutants of concern, particularly fine sediment particles (FSP < 16µm), yet the Crediting Program cannot comprehensively account for SEZ pollutant reductions without such tools. The priority management needs with respect to how Tahoe Basin SEZ restoration can contribute to the TMDL goals; including the ability to estimate the FSP load reduction expected as a result of enhancement efforts on SEZ of any scale. The 2NDNATURE proposed research will begin to address each of these needs by incorporating best available data and information, leveraging existing models and methods, and building upon existing research.

In order to provide an accurate quantification of the actual pollutant load reduction of a specific SEZ restoration effort, many years of high resolution data upstream and downstream of the restoration actions would be required both pre‐ and post‐ restoration. However, this data is costly, time consuming and difficult to obtain reliably. In lieu of extensive site‐specific data collection, the research team believes that existing research and datasets can be integrated with key geomorphic, vegetation and physical characteristics of an SEZ or stream reach and associated floodplain to provide a methodology from which managers can obtain a reasonable estimate of the water quality benefits of SEZs or stream restoration efforts. In order for these methods to be useful to managers, the estimates and outputs of the pollutant load reductions should be consistent with the existing pollutant reduction estimation tools that support the Crediting Program. The 2NDNATURE team provides this synergy with our collective expertise in fluvial restoration actions that continue to occur in the Tahoe Basin (2NDNATURE 2010b), our past and current research to align data collection with method development to quantify fine sediment load reductions from SEZ/stream restoration efforts (2NDANTURE 2006a, 2NDNATURE 2010a), and our intimate involvement in the development and adaptive management of the Tahoe TMDL stormwater tools and associated Crediting Program (LRWQCB and NDEP 2009, nhc et al. 2009, 2NDNATURE et al. 2010b, 2NDNATURE et al. 2009).

C. BACKGROUND AND PROBLEM STATEMENT

The Lake Tahoe TMDL segregates potential sources of the pollutants of concern impairing Lake Clarity (fine sediment particles (FSP) <16µm, total nitrogen and total phosphorus) into 5 source category groups (urban/groundwater, atmospheric, forested upland, stream channel erosion, and shoreline erosion). The Lake Tahoe TMDL Technical Report (LRWQCB and NDEP 2010) estimates that urban areas are responsible for approximately 72% and streams are responsible for 8%, of the average annual FSP loading to Lake Tahoe. While not quantified during the TMDL analyses, SEZs appear to provide significant opportunity to supplement load reductions from urban source control and treatment systems. Typical centralized stormwater treatment BMPs (SWTs) that are constructed to accept and treat stormwater from public and



private lands (e.g., dry basins, wet basins, cartridge filters, bed filters, etc.) usually do not exceed 1 acre in size, nor do treatment volume capacities typically exceed 1.5 acre‐feet of water. Additionally, the remaining public land required to construct new SWTs in urban areas is limited, thus increasing the cost of future SWT implementation. In contrast, SEZs can be a few to hundreds of acres in size, require less continued maintenance than urban stormwater treatment structures to maintain water quality performance, and result in improvements to a number of Beneficial Uses and TRPA thresholds, including habitat, recreational, aquatic and wildlife resources.

The 2NDNATURE team is currently developing a data‐validated methodologies (i.e., SLRT) to quantify the pollutant load reductions achieved by the Trout Creek restoration project with SNPLMA Round 9 research funding (2NDNATURE 2010a). The SLRT end product will include 3 potential methodologies at varying levels of rigor and required datasets to estimate the average annual total and fine sediment load reductions associated with stream restoration efforts. However, there are areas where the SLRT methodology would need to be expanded to meet the broader needs of managers to estimate load reductions of any SEZ interception and/or restoration project.

First, the Trout Creek restoration contains the greatest amount of applicable geomorphic, water quality and hydrologic data of any likely stream reach in the Tahoe Basin. The SLRT methods at the completion of the Round 9 research (expected Fall 2011) will not include a recommended and consistent approach to estimate the hydrology and pollutant loading to the upstream boundary of a stream restoration reach where an adequate long‐term dataset does not currently exist. A method to apply available datasets within the Tahoe Basin to estimate the volume and pollutant loading to the upstream boundary of a stream restoration project is a critical component and would be defined using the SNPLMA Round 11 resources requested herein. This would allow the development of a complete methodology to estimate the average annual load reductions of any stream restoration project in the Tahoe Basin applicable to the TMDL.

Second, the SLRT input and modeling parameters will be developed and calibrated using high resolution water quality data from Trout Creek, a 97‐acre SEZ restoration effort, however, the inputs and computations are hypothesized to be directly applicable to any scale fluvial system. Using the SNPLMA Round 11 resources, the SLRT methodology will be refined and scaled for testing on smaller scale SEZs to provide a recommended method to quantify load reductions from SEZs in these instances. Data obtained during this research will be used to provide preliminary testing, but it is likely that long‐term datasets will be necessary to validate and test these methods over time. The method development to estimate intercepting SEZ pollutant load reduction benefit would include the integration of PLRM hydrologic and water quality outputs as inputs to the upstream boundary of the SEZ in question.

Finally, 2NDNATURE work on Trout Creek and the Upper Truckee River will be used to identify the critical physical, geomorphic and vegetation characteristics of subject SEZ as inputs to the estimation tool. This research will document the recommended parameters, metrics, spatial and temporal resolution of observations required as inputs to the methodology at a reasonable level of detail to guide future users.

D. GOAL, OBJECTIVES, HYPOTHESES

Goal 1. Provide a load reduction estimation approach to quantify load reductions from specific SEZs restoration projects of all potential sizes in the Tahoe Basin given available data and models.

Objective 1. Identify and refine the appropriate SLRT methodology developed using Round 9 funds to meet the current programmatic and regulatory needs of the TMDL and associated crediting program. The methodology will provide recommendations on how to best generate required inputs for any scale of SEZ with any range of existing hydrology and pollutant loading data available.

Hypothesis 1. The SLRT methodology is directly applicable and can be refined to provide reasonable and defensible estimates of pollutant load reductions achieved for all potential scales of SEZs that exist in the Tahoe Basin.



E. APPROACH, METHODOLOGY AND LOCATION OF RESEARCH

LOCATION OF RESEARCH

The 2NDNATURE team will continue to build upon the data collection, analysis and model development work conducted on Trout Creek and the Upper Truckee River. Tangible SEZ examples will be used to develop, test and refine the specific SEZ pollutant load reduction methodology. Three intercepting SEZ sites currently accepting direct runoff from urban catchment outlets will also be analyzed. These intercepting sites will be selected to collectively represent a range of existing functionality.

APPROACH

The SNPLMA Round 11 resources will be used to develop an approach to estimate the annual average pollutant load reductions from the expected scales of SEZ restoration efforts conducted in the Tahoe Basin with a range of available hydrologic data. The development of a reasonable, repeatable and reliable toolbox that quantify project‐specific stream and SEZ restoration water quality benefits on an average annual basis will be based on past and ongoing research of existing datasets in combination with the key attributes of functional stream/meadow/SEZ systems. This research effort will utilize datasets from continued spring snow melt data collection at the currently monitored Trout Creek and Upper Truckee River sites. In addition, three small‐scale intervening SEZ’s will be evaluated during WY2012.Typical SEZ restoration includes geomorphic modifications to oversized channels within an SEZ to increase the likelihood of inundating floodplain areas adjacent to the stream channel, allowing deposition of sediment on the floodplain and decreasing in‐channel shear stress that drives sediment generation via channel erosion. The SLRT approach models these geomorphic and physical concepts and we believe it is potentially applicable on all SEZ scales. Vegetation characteristics of the floodplain will also be considered. The research team will refine and apply the SLRT parameters and approach such that a preliminary methodology will be developed to provide site‐specific estimates of pollutant load reductions for all potential sizes of SEZs encountered in the Tahoe Basin.

METHODOLOGY

The goal of a stream load reduction tool (2NDNATURE 2010a) is to create a repeatable yet cost‐effective methodology to estimate the average annual pollutant load at the downstream reach of a stream restoration project for both pre‐ and post‐restoration conditions. Water quality effectiveness of a stream restoration project (defined as the expected pollutant load reduction as a result of restoration actions) can be assessed as a function of 1) the storage of pollutants that would otherwise have reached downstream areas (floodplain deposition) and 2) the reduction in pollutant generation via stability of the stream banks that would otherwise have eroded (Figure 1). Thus, the SLRT will allow for a load reduction estimate of a stream restoration effort by determining the expected difference in pollutant loading pre‐ and post‐restoration actions. The stream load reduction tool (2NDNATURE 2010a) integrates functional geomorphic and physical characteristics of a stream and associated meadow with sediment transport processes to estimate the pollutant load reduction as a result of specific site restoration actions. On‐going floodplain pollutant retention research on select Tahoe Basin streams suggests overbank flow events do provide FSP retention and concentration reductions via settling, adherence to vegetation, flocculation and stranding (S. Andrews, pers. comm., 2NDNATURE 2006, 2NDNATURE 2010a). The 2NDNATURE team is obtaining detailed site‐specific floodplain retention data and site constrained continuous sediment loading at the upstream and downstream boundary for Trout Creek for 2010 and 2011 snowmelt events in order to inform reasonable retention coefficients for pollutants that access the floodplain (Figure 2). The reduction in channel‐derived sediment as a result of restoration can be estimated using a number of methods that range in complexity and the amount of required data. Figure 3 summarizes the concepts associated with estimating channel sediment generation, and SLRT methodologies will lend from existing models implemented in the Tahoe Basin including Bank Stability and Toe Erosion Model (BSTEM), which calculates erosion rates for particular discharge conditions, and CONservational Channel Evolution and Pollutant Transport System (CONCEPTS), a data intensive channel erosion model.

The outcome from the SLRT (SNPLMA Round 9) effort will be 3 empirically supported methodologies that have a range of complexity and data input requirements to estimate the average annual pollutant load reduction from a stream restoration



project given available hydrologic and pollutant loading datasets. The more complex approaches will be used to validate estimates using the simple approaches. SLRT estimates the expected difference in pollutant loading pre‐ and post‐restoration actions based on changes to specific attributes of geomorphic form and floodplain characteristics that are key to achieving volume and pollutant retention. These methodologies will have be developed and validated only using a section of the Trout Creek Restoration.

The research team will use Round 11 funds to apply and scale these physical and geomorphic concepts to develop a methodology to estimate the load reductions achieved by routing an urban drainage outfall to an intercepting SEZ while preserving the geomorphic concepts applicable to smaller sized SEZ systems. The methodology will be applied to the 3 example intercepting SEZ’s selected to demonstrate application and outputs. Cost‐effective site surveys, hydrologic and water quality data will be collected from the sites as necessary to test assumptions and provide preliminary validation of the applicability of SLRT to intercepting SEZs. The data collection will be scaled based on available resources. The SEZ pollutant load reduction estimates will be limited to total and fine sediment reductions, but future effort could augment these methods with nutrients as desired.

F. RELATIONSHIP OF RESEARCH TO CURRENT EFFORTS

As outlined in the approach, this proposed research will significantly leverage and utilize a wide array of existing datasets. In addition, the proposed research will inform and/or build upon the following Tahoe Basin efforts:

• Stream Load Reduction Tool development (2NDNATURE 2010a) • Riparian Ecosystem Restoration Effectiveness Framework (2NDNATURE et al 2010b) • Methodology to Predict Total and Fine Sediment Load Reductions as a Result of Channel Restoration in Tahoe

Streams (2NDNATURE et al 2010) • Pollutant Load Reduction Model (nhc et al. 2009) • Pollutant Load Reduction Opportunity Report (LRWQCB and NDEP 2008) • Lake Tahoe Total Daily Maximum Load (LRWQCB and NDEP 2010) • Lake Clarity Crediting Program (LRWQCB and NDEP 2009) • Lake Tahoe TMDL Accounting & Tracking Tool (ACOE 2009)

G. ENGAGING MANAGERS

A technical advisory committee (TAC) will be assembled and include stream restoration practitioners, jurisdictional stormwater managers, regulators and technical reviewers. The TAC will be called upon to review and comment on draft products at 2 critical milestones of the project (see task descriptions below). The research team will compile and review existing datasets to refine our proposed Research Strategy to meet the goals of this research. The TAC will be convened to review, comment and reach agreement on the most feasible approach and expected products based on the collective needs and available resources. The addition of Environmental Incentives (the lead developer of the Crediting Program (LRWQCB and NDEP 2009)) will ensure the manager’s technical needs related to the TMDL will be addressed from this research.

H. DELIVERABLES/PRODUCTS

Task 1 Data collection and data management Task 1 includes the site selection, data collection and data management of the 3 intervening SEZ sites. The data collection may include SEZ channel and floodplain surveys, peak flow monitoring, floodplain inundation sampling or other specific data collection necessary to meet the goals of this research given existing resources. Data management and analysis of existing datasets and use of available models will greatly inform method development and be used throughout this research. Task 2 Research Strategy



The research team will identify the recommended appropriate SLRT methodology for refinement to apply to a wide range of both SEZs scales and availability of existing data. Coordinating with Round 9 research, the team will identify data collection and external data analysis needs necessary to meet the goals of this research. Task 3 Technical Reporting of recommended methods Based on the approach and methodology outlined herein, the 2NDNATURE team will provide recommended methods to estimate: 1) Pollutant load reductions expected from stream restoration projects and 2) load reduction benefits if a degraded intercepting SEZ is restored. The methods will include necessary site‐specific data collection and reporting metrics to document pre‐ and post‐restoration physical and geomorphic characteristics of a specific stream or SEZ. The methods will also include recommendations for utilizing available data to determine site hydrology and sediment loading for the upstream boundaries of stream restoration efforts where rich long‐term datasets may not be available. In the instance where the upstream boundary of an SEZ can be modeled using PLRM, the methods will include how PLRM outputs are used as inputs to quantify the SEZ load reduction benefit. The methods will be demonstrated using the selected example stream and SEZ sites. The technical document will summarize the existing data, methods, justification, assumptions as well as identify recommended next steps, limitations and priority data gaps. The TAC will review and provide feedback on the draft analysis. Task 4 TAC meetings A TAC uniting regulatory, local agency and stream restoration practitioners will be convened to provide review and comments on draft findings and preliminary products at two critical milestones of the research. Likely these will occur prior to spring 2012 data collection and to provide review and comment on the draft of deliverable of Task 4. Task 5 Progress Reports Submit quarterly progress reports to SNPLMA in required format.

III. Schedule

Milestone Start Date End Date

Task 1 Compile and manage existing data. Select and conduct field analysis of example SEZ sites as necessary.

July 11 July 12

Task 2 Develop Research Strategy July 11 Oct 11 Task 4: TAC Meeting #1: Review, prioritize and approve strategy Nov 11

Task 3.1 Draft Technical Report Oct 12 Mar 13 Task 4: TAC Meeting #2: Review Draft of Task 3 April 13

Task 3.2 Final Technical Report May 13 July 13 Task 5 Quarterly progress reports July 11 July 13



IV. Literature cited/References

2NDNATURE. 2006a. CSLT Upper Truckee River Sediment Monitoring: Middle Reach (2002‐2005). Prepared for the City of South Lake Tahoe. March 2006. ftp://www.2ndnaturellc.com/2ndnature/2NDNATURE_Reports/Lake%20Tahoe/UTRSedimentStudy_FinalReport.pdf

2NDNATURE. 2006b. Detention Basin Treatment of Hydrocarbon Compounds in Urban Stormwater. Final Technical Report. Prepared for South Lake Tahoe Public Utility District. March 2006. ftp://www.2ndnaturellc.com/2ndnature/2NDNATURE_Reports/Lake%20Tahoe/Detention%20Basin%20Treatment%20of%20Hydrocarbon%20Compounds%20in%20Urban%20Stormwater%202006.pdf

2NDNATURE. 2008. Water Quality Performance Evaluation of Park Avenue Detention Basins; South Lake Tahoe,CA. Final Technical Report. Prepared for City of South Lake Tahoe Engineering Division. August 2008. ftp://www.2ndnaturellc.com/2ndnature/2NDNATURE_Reports/Lake%20Tahoe/Water%20Quality%20Performance%20Evaluations%20of%20Park%20Ave%20Detention%20Basins%202008.pdf

2NDNATURE. 2010a. Quantification and Characterization of Trout Creek Restoration Effectiveness; Focused Development of a Stream Load Reduction Methodology (SLRT). Prepared for the USFS, Lake Tahoe Basin Management Unit. April 2010 ftp://www.2ndnaturellc.com/2ndnature/2NDNATURE_Reports/Lake%20Tahoe/SLRT_Trout%20ChPlan_Final%20April%202010.pdf

2NDNATURE. 2010b. Riparian Ecosystem Restoration Framework; Tracking the Benefits of Stream and Floodplain Restoration in the Lake Tahoe Basin. Prepared for the USFS, Lake Tahoe Basin Management Unit. January 2010 ftp://www.2ndnaturellc.com/2ndnature/2NDNATURE_Reports/Lake%20Tahoe/Riparian%20Ecosystem%20Restoration%20Framework__FINAL.pdf

2NDNATURE and Northwest Hydraulic Consultants (nhc). 2010a. PLRM Refinement Monitoring: Phase II. Final Monitoring Plan. Prepared for USFS Lake Tahoe Basin Management Unit. July 2010. ftp://2ndnaturellc.com/2ndnature/2NDNATURE_Reports/Lake%20Tahoe/PLRMRefinement_FinalPhaseII_MonitoringPlan.pdf

2NDNATURE and nhc. 2010b. PLRM, Focused Stormwater Monitoring to Validate Water Quality Source Control and Treatment Assumptions. Final Technical Report. Prepared for US Army Corps of Engineers, Sacramento District. March 2010. ftp://2ndnaturellc.com/2ndnature/2NDNATURE_Reports/Lake%20Tahoe/PLRM%20Refinement_FinalPhaseI_TechnicalReport.pdf

2NDNATURE and nhc. 2011. PLRM Refinement Monitoring: Phase II. Final Technical Report. Prepared for USFS Lake Tahoe Basin Management Unit. Expected December 2011.

2NDNATURE, nhc and Environmental Incentives (EI). 2009. BMP Maintenance Rapid Assessment Methodology (BMP RAM) Technical Document and Users Manual. Lake Tahoe, CA. Prepared for the Army Corps of Engineers. September, 2009 http://www.swrcb.ca.gov/rwqcb6/water_issues/programs/tmdl/lake_tahoe/

2NDNATURE, nhc, and EI. 2010a. Pilot catchment scale testing of Lake Tahoe stormwater tools. Funded by the Army Corps of Engineers. Contract awarded September 2010.



2NDNATURE, nhc and EI. 2010b. Road Rapid Assessment Methodology (Road RAM) Technical Document and Users Manual, Tahoe Basin. Prepared for the California Tahoe Conservancy and Nevada Division of Environmental Protection. Expected November 2010.

2NDNATURE, nhc, and EI 2011. Placer County Stormwater TMDL Strategy. Final Technical Report. Prepared for Army Corps of Engineers and Placer County. Expected March 2011

US Army Corps of Engineers (ACOE). 2009. Lake Tahoe TMDL Tracking Tool is the accounting database tool used by urban jurisdictions and program managers to submit, approve and track catchment load reductions and associated credit schedules. Version 1 of the TMDL Tracking Tool was released by 2NDNATURE and Environmental Incentives in October 2009 and funded by the Army Corps of Engineers. Lahontan Regional Water Quality Control Board (LRWQCB) and Nevada Division of Environmental Protection (NDEP). 2008. Lake Tahoe TMDL Pollutant Reduction Opportunity Report. March 2008 http://www.waterboards.ca.gov/lahontan/water_issues/programs/tmdl/lake_tahoe/docs/presentations/pro_report_v2.pdf LRWQCB and NDEP. 2009. Lake Clarity Crediting Program Handbook. Developed by Environmental Incentives. September 2009. http://www.swrcb.ca.gov/rwqcb6/water_issues/programs/tmdl/lake_tahoe/index.shtml

LRWQCB and NDEP. 2010. Tahoe Basin Total Maximum Daily Load, Technical Report. California and Nevada. June 2010. http://www.swrcb.ca.gov/rwqcb6/water_issues/programs/tmdl/lake_tahoe/index.shtml

nhc, Geosyntec Consultants, and 2NDNATURE. 2009. PLRM Model Development Document. Prepared for Lake Tahoe Basin Stormwater Quality Improvement Committee. South Lake Tahoe. CA. A complete Users Manual as well as full source code and other supporting documents can be downloaded from www.tiims.org.

Schwarz, G.E., Hoos, A.B., Alexander, R.B., and Smith, R.A., 2006, The SPARROW Surface Water‐Quality Model Theory, Applications and User Documentation: U.S. Geological Survey, Techniques and Methods 6–B3, 248 p. and CD –ROM.



Figures

Floodplain Stream

Sediment Load IN

Floodplain

Streamreach

Sediment Load OUT

Sediment deposition

2 1 2

1 Deposition pre-restoration 2 Additional deposition post-restoration

1

Sediment deposition

Channel erosion Channel erosion

Simplest conceptual model: For a given stream reach, transfer of mass (water, sediment) is from the stream to the floodplain and of mass (sediment) from the banks to the stream. The amount of sediment sequestered on the floodplain or produced by channel erosion depends on factors that reflect the physical and biogeochemical processes acting on the total and fine (<16 μm) sediment.

General structure of SLRT models: field measurements of water quality and channel and floodplain characteristics (blue) constrain calculations of floodplain inundation, channel erosion, and floodplain deposition (green). Information and/or data needed to validate and improve calculations are noted in green boxes within parentheses. The difference between sediment load inputs and outputs represents the water quality benefit of the reach. Comparison of the output pre- and post-restoration indicates the net water quality benefits of the project.

Water discharge(USGS gages)

Channel and floodplain geometry(cross-sections, roughness)

TSS and FSP concentrations(USGS and others)

Water elevation and floodplain inundation(HEC-RAS, HEC-geoRAS, stage recorders)

TSS and FSP load input to reach(water quality mmts.)

Floodplain factors:topo. complexity, vegetation, soils

(field observations)

Floodplain retention or bypass of TSS/FSP load(water quality mmts., sediment pins, surveys)

Bank factors:lithology, vegetation, height

(field observations)

TSS/FSP load generation from bank erosion within reach(cross-sections)

TSS and FSP load output from reach(water quality mmts.)

FIGURE 1SLRT CONCEPTUAL MODELING APPROACH

from 2NDNATURE et. al. (2010)

Water discharge (cfs)

Freq

uenc

y of

occ

urre

nce

(day

s)


Flo

od

pla

in a

rea

floo

ded

(hec

tare

s)

pre-restoration

post-restoration


post- pre-


TSS

and

FSP

lo

ad (t

on

nes

/day

)


Rete

nti

on

co

effic

ien

t (C

r)

to be determined by stream andfloodplain measurements

?

1 2

3 4

Floodplain deposition model: Deposition on the floodplain for total and fine sediment can be determined in the simplest case using water quality (1) and water discharge data (2) to determine the amount of sediment transported during discharge conditions with inundation post-project but not pre-project. The model can be made more complex by incorporating additional data from floodplain measurements to determine a retention coefficient that estimates the fraction of TSS and FSP load retained on the floodplain for different discharge conditions pre- and post-project (3). The retention coefficient is based on floodplain factors such as vegetation height and density, floodplain area, and topographic complexity. The most complex case incorporates a model of 2D flow to determine specific areas inundated for different discharge conditions (4). We hypothesize that the primary water quality benefit from floodplain deposition occurs at intermediate discharge values between inundation post-project and inundation pre- and post-project (bottom graph between red lines).

no

flo

od

pla

inin

un

dat

ion

inu

nd

atio

np

ost

-res

tora

tio

no

nly

inu

nd

atio

np

re- a

nd

po

st-

rest

ora

tio

n

TSS

FSP

Av

era

ge

an

nu

al

sed

ime

nt

(TSS

an

d F

SP) r

etai

ned

on

flo

od

pla

in (t

on

nes

/yea

r)

FIGURE 2FLOODPLAIN DEPOSITION MODEL COMPONENTS FOR SLRT


FIGURE 3 CHANNEL EROSION MODEL COMPONENTS FOR SLRT


Wat

er d

epth

(ft)

post-restoration

pre-restoration


Sed

imen

t pro

duc

ed (

TSS

and

fin

es)

by

chan

nel

ero

sio

n(a

mo

un

t p

er t

ime)

Elev

atio

n (ft

)

Distance (ft)

2

4 5

1

Channel erosion model: Generation of total and fine sediment by erosion of the channel can be determined in the simplest case using changes in average channel water depth for a given discharge (1) from lowering bank heighs and/or raising bed elevation, and in channel gradient (shown as changes in the longitudinal profile in 2) from increasing sinuosity. The intermediate-complexity case adds additional parameters to consider the probability of particular water discharge occurrence (3) and to separately model vertical incision and stream bank erosion (4). In the complex case, a 2D model (HEC-geoRAS or CONCEPTS) would calculate vertical and horizontal erosion for multiple cross-sections, thereby producing 2D erosion results (5). The cumulative water quality benefit is greatest at intermediate water discharge conditions (bottom graph).

pre-restoration

post-restoration

E1~k

1τ

E2~k

2τ


3

post-

pre-Fr

eque

ncy

of o

ccur

renc

e (d

ays)


tools to quantify urban stormwater load reduction … seabright ave, suite 205 santa cruz,...

Documents