Golder Associates
October, 20, 2009 Project No. 07-1450-0111
Mr. Larry Wiens
Dewdney Area Improvement District
PROPOSAL OVERVIEW
HATZIC VALLEY FLOOD MANAGEMENT INFRASTRUCTURE PLAN
This business plan was prepared on behalf of the Dewdney Area Improvement District (DAID) in support of an application to Emergency Management BC (EMBC) for design and construction of a “fish friendly” pump station at Hatzic Lake, Mission BC, refer to Figure 1 attached. This business plan presents a proposed framework for multi-phase flood risk reduction for the Hatzic Prairie/ Dewdney Area.
1.0 PROJECT SYNOPSIS
Frequent flooding within the Hatzic / Dewdney area occurs as a direct result of the inadequate pumping capacityof the existing pump station and a history of inadequate channel maintenance/sediment removals within the primary drainage channels.
The Hatzic Lake watershed area, situated east of Mission on the north side of the Fraser River (Figure 1), covers approximately 90 km2. Half of the watershed is covered by steeply sided mountains, some of which have been partially logged. Level, arable land is situated around the east and north sides of Hatzic Lake and accounts for 25.3 km2 of the watershed. Hatzic Lake covers an area of 3.37 km2.
Runoff from the watershed is carried primarily by Legace Creek which has a major tributary in Pattison Creek and originates in the Douglas Forest 15 km northeast of Mission and flows southward 10 km before entering Hatzic Lake. Runoff from the creek and the adjacent Hatzic Slough is eventually discharged into the Fraser River through the existing pump station and floodboxes (Figures 2 and 3).
Legace Creek and Hatzic Lake have experienced persistent flooding problems over the last 65 years due to three main causes:
Flooding of Hatzic Prairie and Lower Legace Creek from backwater of Hatzic Lake due to inadequate pumping capacity;
Flooding of Hatzic Prairie from Legace Creek breaking out of its channel due to channel avulsions and sediment infilling; and,
Channel aggradation and sediment infilling on the Legace-Pattison Creek Fan caused by high debris and sediment loads in the creeks. Sediment sources are related to landslides and previous logging in the catchment headwaters.
The frequency and prolonged duration of flood events significantly impacts the productivity of the agricultural lands and negatively impacts residential and recreational values. A critical failure of the existing pump station during a major storm event would not only impact the population and farmland behind the Dewdney Dike but could also impact the Lougheed Highway, the CP rail lines and the Dewdney Dike itself.
Based on land assessments carried out in 2008, the total market value of the land in the district is $205 million.This is based on a total of 548 properties consisting of 236 properties on Hatzic lake and 312 farm properties surrounding the lake. The assessed value of the farm properties was at about 50 per cent of the total assessed value of $205 million. Considering that the assessed value of farmland is significantly lower than actual resale value, based on recent transactions, the actual value of the properties within the affected area is likely significantly more than the $205 million dollar assessed value.
Historically, the board of trustees for DAID has been responsible for maintenance of the Dewdney Dike and maintenance and operation of the Hatzic pump station. Capital expenditures related to the pump station and flood mitigation relating to sediment accumulation in Hatzic Slough, Legace/Pattison Creek and all of the tributary drainages to the north and east of Hatzic lake has been the responsibility of the Provincial Government.In recent years, the responsibility for flood mitigation has been re-assigned to local regional districts, however the Fraser Valley Regional District (FVRD) lacks the resources and the taxation structure to deal with these flooding issues. As there is no other regulatory agency that has a mandate to deal with flooding issues within
the Hatzic / Dewdney area, the board of trustees for DAID has provided funding from local residents to develop a comprehensive plan to deal with these issues.
DAID is seeking funding from Emergency Management British Columbia (EMBC) to fund a framework of mitigation measures to reduce the risk and duration of flooding within the Hatzic / Dewdney area. This document provides an overview of the flood risk reduction and fish access framework.
1.1 Framework of Program
A framework of studies and construction tasks has been developed to address the flooding and fish access issues in the Hatzic/ Dewdney area. The key issues to be resolved are as follows:
Flood Risk Reduction - Increase the pump station capacity to maintain adequate conveyance of storm runoff during flood events. This can be achieved by installation of a new primary “fish friendly” pump station. The existing station would be maintained as a supplementary station.
Sediment Management - As noted, there is a large volume of accumulated sediment within the major drainage channels that drain the Hatzic / Dewdney area. A multi-stage program of sediment removal is proposed to re-establish channel conveyance to allow adequate capacity for flows to reach the pump stations. It is important to note that there is a large volume of sediment in the upper catchment area as a result of previous logging operations and landslides, thus any program of flood risk reduction must include an allowance for sediment management, which will be ongoing. DAID must plan in terms of repeated regular removals and any discussions with permit agencies must indicate the priority for sediment removals to be included in any program of flood hazard reduction. A long-term commitment to ongoing sediment management, including removals, must be included in the program.
Fish Access Improvements - For any program to be considered by the Department of Fisheries and Oceans (DFO) and Ministry of Environment (MoE), improvements for fish access into Hatzic Lake should be included. The proposed flood mitigation program will provide significant fish access improvements. This would include installing modern fish friendly pumps in the new pump station and installation of a fishway within at least one of the flood boxes through the Dewdney dike. The proposed channel dredging program will also provide significant fish access improvements once fish enter Hatzic Lake. At present, once the water level in the lake drops, access from the channel within the lake to both Hatzic Slough and
Legace/Pattison Creeks and Chilqua Slough as well as creeks on the west side of the lake is restricted due to sediment deposition. Thus, channel improvements should be considered for fish access as well.
2.0 PROJECT DETAILS
2.1 Background
Dewdney Area Improvement District consists of several areas surrounding Hatzic Lake including:
A primarily agricultural area located north of Hatzic Lake referred to as Hatzic Prairie;
A relatively high density residential area referred to as Hatzic Island;
A second mainly agricultural area located east of Hatzic Lake, referred to as Hatzic Prairie East; and,
A third agricultural area located south and east of Hatzic Lake referred to as Dewdney.
All of these areas are protected from Fraser River flood events by the 12 kilometre long Dewdney Dike (refer toFigure 2).
All of these areas are at risk not only from Fraser River flood events during spring freshet but also from internal flooding related to storm events within the catchment area. Flooding within the Hatzic / Dewdney area occurs as a direct result of the inadequate pumping capacity of the existing pump station and a history of inadequate channel maintenance/sediment removals within the primary drainage channels.
During the last several years, the flooding issues that affect the areas to the north and to the east of Hatzic Lake have become exacerbated as a result of sediment infilling of the major drainage channels and within Hatzic Lake itself. Of note is the extensive deposition that is occurring to the north of Hatzic Island. It is likely that ongoing deposition may now be constraining the channel conveyance and causing creek levels and groundwater levels (in Hatzic Prairie and Hatzic East) to rise, refer to Figure 4. There has been a long duration between large-scale cleanouts of the primary drainage creeks in Hatzic Prairie (including Pattison Creek and Legace Creek), as summarised below:
1991 – 96,000 m3 of sediment was removed;
2001 – 7,000 m3 of sediment was removed;
2002 – 13,000 m3 of sediment was removed; and,
2005 – 110,000 m3 of sediment was removed.
A regular and coordinated sediment removal program has not been implemented for the Hatzic/Dewdney area and is one of the recommended objectives of the flood risk reduction framework.
It is expected that if left unresolved these potential flooding issues will continue to worsen and this will significantly impact the value of all of the agricultural and residential lands within the Hatzic / Dewdney area. In order to mitigate the potential impact of flooding issues that affect the Hatzic / Dewdney area, sufficient pumping capacity must be installed and the primary drainage channels must be maintained to the minimum target depth
required to allow adequate conveyance of runoff water to the pumping station.
It is also important to note that the accumulating sediments at the north end of Hatzic Lake represent a potential impediment for any fish species that would spawn in the upland areas north and east of Hatzic Lake. If minimum channel elevation levels are not restored and maintained on a regular basis all fish access and fish habitat in the affected area will be severely impacted.
Therefore, installation of a new primary pump station utilizing “fish friendly” pumps to increase total pumping capacity, completion of the proposed drainage works and implementation of an ongoing sediment management program would significantly reduce flood frequency and duration and improve fish access in the subject area.
2.2 Economic Evaluation of Hatzic Prairie
In 2006 the BC Ministry of Agriculture and Lands (1) reported on the agricultural production of Hatzic Prairie Area and Agriculture on the Hatzic Prairie Area and the impacts of frequent flooding on the agricultural production rates, as summarized below:
Agriculture is well established on the Hatzic Prairie; with a long history of crops grown in the area. Agriculture on the Hatzic Prarie is long standing and economically viable due to the excellent growing conditions, good soil, good climate, appropriate parcel sizes, and proximity to markets. More recent developments on the agricultural land base in Hatzic Prairie reflect the area's increasing challenges to farming operations due to flooding. Of the 963 ha of land in Hatzic Prairie, approximately 642 ha are in production. Between 2001 and 2005, flooding almost tripled the land base classified as marginal or unused: in 2001 there were 14 parcels totalling 120 ha in this category while in 2005, the area classified as marginal or unused increased to 40 parcels equalling 332 ha. There is an ongoing and cumulative economic impact that flooding and poor drainage are having on the agriculture producers in the area. Losses for 2005 alone using current agricultural usses were calculated to fall between $832.000 as a conservative estimate to over $2,000,000. Due to the areas otherwise excellent growing conditions, many local farmers have indicated they would invest further in their agriculture businesses if drainage were improved.
Agricultural businesses need room to expand to meet local and national food and product demands. As a
result, overall farm gate receipts for agricultural businesses are increasing at a rate even greater than local population growth. Improving and maintaining the drainage in Hatzic Prairie to an Agri-Food Regional Development Subsidiary Agreement (ARDSA) criterion would allow for the development of higher value agriculture in Hatzic Prairie and enable agriculture businesses to be more viable. It would also redress a few of the land constraint problems faced by agri-businesses. In the event that local farmers gain confidence in the drainage of the land and invest in higher agricultural production, such as blueberry or nursery production, the estimated annual return would range from $12,300,000 to $16,932,000, respectively.
2.3 Previous Work
DAID has as its mandate the provision of flood protection for the land and properties within the District. The DAID mandate is carried out by operation and maintenance of the Hatzic Pump Station, maintenance of the Dewdney Dike (about 12 km in length extending from Lougheed Highway, just west of Shook Road, along the Fraser River eastward to the intersection of Bell Road and Lougheed Highway). DAID are also involved with management of sediment delivered to the lake and upstream creek channels to maintain fish access, water conveyance and lake active storage. A number of studies have been completed dealing with issues relating to the Hatzic Lake flood risk reduction and fish access and are summarised below:
In 2003 Golder Associates(2) (Golder) presented a strategic plan for the upgrade of the Hatzic pump station.
As part of this strategic plan, Golder reviewed fisheries issues within the watershed, identified concepts for the pump station upgrade and evaluated costs and advantages of each upgrade. The present hydraulic capacity of the pumps is about 6.06 m3/s, which is insufficient to drain Hatzic Slough during significant flood events. Golder indicated that the minimum required pump capacity is 14 m3/s with a recommended upgrade to 20.5 m3/s. Golder also indicated that if the lake level is operated at El 2 m, the combined flood storage and a total pump capacity of 14 m3/s will enable the 1:10 year, 10 day duration flood to be released to meet the ARDSA criteria.
The present pump station is considered to be a significant barrier to fish and is of concern regarding fish
mortality associated with pump operation. Based upon discussions with DFO during the Golder (2003) study, it was determined that fish access into Hatzic Slough is considered a high priority with the reviewing agencies; accordingly, any proposal to upgrade the pumping capacity to minimize the flood risk to the lake residents and the upstream agricultural properties must consider improvements for fish access.
It is understood (DAID, pers.comm) that a program of gravel removals was undertaken within Legace/Pattison Creek upstream of Hatzic Lake by the FVRD. It is noted that ongoing siltation within Hatzic Lake has limited access for fish into the Pattison/ Legace Creek watershed, especially during late summer low flow periods. Siltation within the lake is expected to continue for some time into the future, as a result of the supply of sediments being delivered from the upper catchments of this watershed due to past logging practices and steep unstable slopes.
In 2007 Golder studied the implementation of a fish ladder structure within one of the existing concrete flood boxes within the dike and the management of the late season water levels within Hatzic Lake for recreational purposes. It is understood that the concept is generally considered acceptable by DFO and MOE, although final approvals have not been provided.
In April 2009, Associated Engineering completed a conceptual design and cost estimate for a new ”fish friendly” pump station on Hatzic Lake with a pump capacity of 8 m3/s. The combination of the existing pump station (capacity of 6.06 m3/s) and the porposed pump station capacity of 8 m3/s will provide a total capacity of 14 m3/s which is required to release the 1 in 10 year, 10 day duration flood event.
2.4 Present Conditions at Hatzic Lake, Hatzic Slough and Legace/Pattison Creek
The mouth of Hatzic Slough provides limited flow conveyance due to the excessive amount of sediment deposition; the remaining channel as it enters the lake makes a sharp left turn (facing downstream) towards the left side of the lake and then turns to the south toward the outlet. Of note, however, is the extensive deposition that is occurring throughout the lake to the north of Hatzic Island. It is likely that ongoing deposition may now be constraining the channel conveyance and causing creek levels and groundwater levels to rise. The deposition is likely reducing the active storage of the lake (i.e., the operational level of the lake), and impeding fish access and may be detrimental to fish spawning areas. Figure 4 presents an air photo of Hatzic Lake showing the extent of sediment deposition.
Legace/Pattison Creek demonstrates a high sediment load and degradation due to upstream sediment delivery and channel works. It is understood that extensive localized removal of deposited sediments has occurred at several times over the past 30 to 40 years, and existing channel works serve to limit the floodplain for the creek itself. It is understood that the FVRD undertook gravel removals since about 2003, but infilling of the channel has occurred since that time. In order to accommodate ongoing sediment aggradation within the creek, sediment traps and localized sediment removals must be considered. A low impact floating dredge is considered potentially suitable to excavate/re-establish a channel within Hatzic Lake. Sediment removals should
be considered as ongoing (i.e., annual/ bi-annual operation, as needed), as the sediment sources are significant and persistent within the watershed; accordingly, a long term sediment management plan should be developed.the impacts of frequent flooding on agricultural production rates, as summarized below:
2.5 Construction Tasks and Study Details
This section summarizes the flooding issues within the Hatzic/Dewdney area and provides the framework for a multi-stage (ie: multi-year) mitigation program that will resolve these issues. On completion of the flood mitigation works described in this application, it is intended that a program of ongoing maintenance of the drainage channels will be established to facilitate long-term management of the system.
The framework for resolution of the above issues at Hatzic Lake has been developed into a 3 year plan with ongoing maintenance after the 3rd year. The framework has been broken into work required for each year and is described below:
Year 1 –Engineering Design and Environmental Permits/Approvals and Pump Station Construction
− Detailed design of the proposed pump station and detailed sediment management plans for Hatzic Lake and Hatzic Slough inlet.
− Construction of the proposed “fish friendly” pump station.
Studies to be undertaken by DAID will include the following:
− Detailed survey of Hatzic Lake and the Hatzic Slough / Chilqua Slough Inlet and Legace Creek.
− Engineering design for fish passage/access past the existing dike on Hatzic Slough.
− Further refinement of in lake gravel removal and sediment management plans including identification of optimal areas for gravel removals and establishment of target elevations.
Year 2 – Lake Sediment Removal and Fish Access
− An updating of the Associated Engineering 1992 study on drainage in Hatzic Prairie. This would include revision of the sediment yield estimates for Legace /Pattison Creek, review of more recent water level and rainfall data and preparation of revised excavation and diking plans for the Legace /
Pattison Creek areas.
− Detailing of in channel sediment removal plans including access locations, creek reach cleanout areas, location of sediment traps and location of areas to store sediment removals. This study will be carried out in conjunction with the FVRD, DFO and MoE.
− Improve fish access and conveyance with the removal of sediment deposits in Hatzic Lake.
− Construct lake maintenance/sediment removal. The lake sediment removal and lake channel maintenance could be potentially be undertaken with a low impact floating dredge.
− Construct fishway.
Year 3 – Upstream Channel Improvements and Maintenance Planning
− Planning for long term management of sediment in Hatzic Slough/Legace/Pattison Creeks, this may include regular removal of sediment, implementing catchment management practices to reduce sediment generation.
− Sediment removal in the Hatzic Slough/Legace/Pattison at selected locations within the reach extending from the vicinity of the Pattison Bridge downstream to about Farms Road.
− Install sediment traps along Hatzic Slough/Legace/Pattison Creeks complete with access locations and Rights of Way (ROW) for regular cleanout.
Year 4 and Onwards – Self Administered Program
−
Continuance of the long term maintenance plan which will include operation and maintenance of the pump station, regular clean out and maintenance of sediment traps and removal of the Hatzic Lake sediment deposits.
Figures 2, 3, 4, 5 and 6 present overview plans of the proposed works.
3.0 PROJECT PLAN
The following sections provide a preliminary plan to complete the proposed works.
3.1 Project Deliverables
The deliverables for this project are:
A primary pump station designed to maintain adequate water levels in Hatzic Lake during flood events. The present hydraulic capacity of the pumps is about 6.06 m3/s, which is insufficient to drain Hatzic Slough during significant flood events. The minimum required pump capacity is 14 m3/s and a concept design has been completed to construct a new “fish friendly” pump station at Hatzic Lake with a capacity of 8 m3/s to provide a combined total pump capacity of 14 m3/s.
Increased conveyance through the east side of Hatzic Lake by removing accumulated sediment whilst also improving fish access.
Increased conveyance of Hatzic Slough and Legace/Pattison creeks by removing accumulated sediment whilst also improving fish access.
Design of Sediment Traps and a Maintenance plan and schedule.
3.2 Project Costs
Preliminary cost estimates have been developed for the project based on discussion with contractors and experience with similar projects. All cost estimates exclude GST and PST. Contract awards for the project will be managed in accordance with British Columbia relevant policies and procedures and be transparent, competitive and consistent with value for money principles.
3.3 Year 1 –Pump Station Design and Construction
A summary of costs for the detailed design of the pump station and pump station construction.
Task Unit Rate Quantity Total CAD $
Pump Station Design $ 200,000 1 $ 200,000
Environmental Assessment/Permitting $ 70,000 1 $ 70,000
QA / QC Construction $ 200,000 1 $ 200,000
Electrical Upgrade* See note below
Construction of Pump Station (Materials) $ 2,500,000 1 $ 2,500,000
Construction of Pump Station (Equipment and Labour) $ 1,086,000 1 $ 1,086,000
Contingency $ 350,000 1 $ 350,000
DAID Administration $ 200,000 1 $ 200,000
Total $ 4,606,000
*Additional information is required from BC Hydro to determine if a major upgrade of the electrical supply is required. If a major electrical supply upgrade is required, DAID has the authority to self fund this work through taxation if required.
3.3.1 Year 1 – Engineering Design, Environmental Studies
A summary of costs for an overall flood risk reduction/sediment management/fish access improvement plan is detailed below:
Task Unit Rate Quantity Total CAD $
Lake and Channel Surveys* $ 20,000 1 $ 20,000
Fishway Conceptual Design* $ 15,000 1 $ 15,000
Lake Sediment Removal Design* $ 15,000 1 $ 15,000
Total $50,000.00
*The majority of funding for this task has already been obtained.
3.4 Year 2 – Lake Sediment Removal and Fish Access
3.4.1 Fishway within the Dike
Task Unit Rate Quantity Total CAD $
Environmental Studies / Permitting $ 30,000 1 $ 30,000
Construction of Fishway (Equipment and Labour)* $ 100,000 1 $ 100,000
Construction of Fishway Supply of Materials* $ 250,000 1 $ 250,000
Total $380,000.00
* Note: includes 30% contingency
3.4.2 Sediment Removal and Channel Improvements (within Lake)
It is assumed that a 10 m wide channel, with sideslopes of 4H:1V will be excavated to a depth of about 1.0 m, for a total estimated length of about 2,200 m arriving at a total volume of about 31,000 m3. The material will be dredged, not excavated, at an estimated cost of $10/m3. It is proposed that a laydown area south of Chilqua Slough be considered for containment of the removed sediment.
Task Unit Rate Quantity Total CAD $
Engineering Design, Surveying, Site Supervision, Asbuilt Drawings $ 40,000 1 $ 40,000
Environmental Studies / Permitting $ 40,000 1 $ 40,000
Construction of Lake Sediment Removals (Equipment and Labour)* $ 400,000 1 $ 400,000
Total $480,000.00
* Note: includes 30% contingency
No gain from the sale of the dredgeate has been included. Costs for access, and laydown area Right of Way have not been included.
3.4.3 Design of Upstream Channel Improvements in Legace/Pattison Creeks
This study will include an update of the 1992 Associated Engineering study of drainage for Hatzic Prairie and will include sediment yield estimates, locations where sediment removals are required to increase creek flow capacity, locations for installation of sediment traps and access locations and long term creek channel maintenance planning. Consultation with regulatory agencies (FVRD, MoE, DFO), stakeholders and local residents will be required.
Task Unit Rate Quantity Total CAD $
Update of 1992 Report and Sediment Maintenance &
Planning and Design for Upstream Drainage Channels $ 150,000 1 $ 150,000
Environmental Studies / Permitting $ 40,000 1 $ 40,000
Total $190,000.00
3.5 Year 3 - Upstream Channel Improvements (Legace /Pattison Creeks) and Maintenance Planning
3.5.1 Construction of Channel Improvements (upstream of Lake)
It is assumed that significant sediment removals will be required along Legace and Pattison Creeks and that sediment traps will be installed to allow for future management of creek sediment. Rights of Way (ROW), access to sediment traps and laydown areas for sediment will be required. Consultation with regulatory
agencies (FVRD, MoE, DFO), stakeholders and local residents will be required.
Task Unit Rate Quantity Total CAD $
Engineering Design, Surveying, Site Supervision, Asbuilt Drawings $ 50,000 1 $ 50,000
Environmental Studies / Permitting $ 25,000 1 $ 25,000
Construction (Equipment and Labour)* $ 850,000 1 $ 850,000
Total $925,000.00
* Note: includes 30% contingency
No gain from the sale of the excavated material has been included. Costs for access, laydown area and ROW have not been included.
4.0 CLOSURE
We trust the information contained in this report is sufficient for your immediate requirements. Should you have any questions regarding the above, or if your require further information, please do not hesitate to contact us.
Yours very truly,
GOLDER ASSOCIATES LTD.
___________________________________________________________________________________________________________________________
1 BC Ministry of Agriculture and Lands, Estimate of Economic Impact of Flooding and Poor Drainage on Hatzic Prairie and Economic Potential of Area, April 2006.
2 Golder Associates Report, Hatzic Lake Pump Station Upgrade Strategic Plan, July 2003.
Figure 1 - Key Plan
Figure 2 - Site Plan and Proposed Works
Figure 3 - Conceptual Management Plan Hatzic Valley Watershed
Figure 4 - Hatzic Lake Plan
Figure 5 - Hatzic Lake Conceptual Sediment Management Plan
Figure 6 - Legacy and Pattison Creek Conceptual Sediment Management Plan