720 University Avenue, Suite 200 Los Gatos, CA 95032 408.458.3200 www.harveyecology.com
Memorandum
October 29, 2025 Project # 4907-01
To: Michelle Huber, StudioBondy Architecture; Mara Chase, Carey School
From: Kelly Hardwicke, H. T. Harvey & Associates
Subject: Riparian Setback Assessment for Early Childhood Center for Carey Schoool Project, City of San Mateo, San Mateo County, California
Executive Summary. This memorandum was prepared to document the appropriate riparian setback for a construction of a new Early Childhood Center for Carey School at 1 Carey School Lane in the City of San Mateo.
The Early Childhood Center (project) would be located at an adjacent parcel, at 2033 LaSalle Drive, Assessor’s Parcel Number (APN)-039040080 (Figure 1). An unnamed creek serves as the property line between the 2033 LaSalle Drive project parcel and Carey School. This memorandum summarizes the habitat characteristics of the unnamed creek and riparian corridor located along the north edge of the creek, and provides our opinion of the appropriate, San Mateo -required riparian setback . The project parcel was evaluated by qualified biologists to determine the limits of sensitive riparian habitat within the unnamed creek, the TOB, and also to evaluate the potential for impacts to this habitat from the project. Using this data, setbacks appropriate to City codes were established (Figure 2), and new project buildings will entirely avoid these setbacks. No riparian trees will be removed by the project, and there will be no encroachment into riparian habitat beyond the existing development.
The project is expected to have only minor, temporary, self restoring impacts to riparian habitat and no impacts to the creek itself.
Regulatory Setting. The City of San Mateo has a city-wide setback requirement for waterways, Municipal Code
7.39.130: Watercourse Protection (City of San Mateo 2024)
1. Development setback from the unnamed creek was
determined as described in Municipal Code 7.39.130 (a) and (b)(3). Additionally, our riparian setback assessment evaluated the riparian setback from the unnamed creek in accordance with the s lope setback requirements applicable to stream banks described in City of San Mateo Slope Development Standards, pages 2-6 (City of San Mateo 1998).2 We have also mapped and discussed the minimal and less than significant potential impacts to
1 City of San Mateo. 2024. City of San Mateo Municipal Code, City of San Mateo Law Library. Accessed at:
https://law.cityofsanmateo.org/us/ca/cities/san-mateo/code in November 2024 2 City of San Mateo. 1998. Slope Development Standards: Questions and Answers about Building on Sloped Property .
Available from https://www.cityofsanmateo.org/DocumentCenter/View/92653/Slope-Development-Standards 2 H. T. Harvey & Associates
sensitive riparian habitat associated with the unnamed stream, which are typically analyzed under CEQA Appendix G, Biological Resources Guideline B , which covers impacts to riparian habitat and other sensitive natural communities.
Methods. H. T. Harvey & Associates plant and wetland ecologist Katherine Marlin, M.S., conducted a reconnaissance-level survey of the project site , defined as parcel 039040080 on October 30, 2024. The purpose of the survey was to provide creek and riparian habitat mapping, including top of bank and riparian dripline, and to measure various creek dimensions such as average depth and horizontal bank distance to apply the correct slope setback methods. We also mapped the location of top of bank (TOB), as well as the riparian dripline on the north bank of the creek, using sub-meter GPS. Creek depth was estimated using an inclinometer and verified using ESRI’s aggregated topographic LIDAR data for the area (ESRI, 2024). Top of bank was mapped for the northern creek bank using methods from A Field Guide to the Identification of the Ordinary High Water Mark (OHWM) in the Arid West Region of the Western United States: A Delineation Manual (USACE 2008). 3 Within the riparian dripline and creek banks, we mapped sensitive riparian habitat. Riparian habitat was mapped based on the canopy line of trees rooted within TOB and changes in the vegetative community, from the understory species described in the preceding paragraph, to planted, ornamental species. Riparian habitat would also include all areas below the TOB. However, it should be noted that the areas underneath the riparian canopy that overhang TOB at this site were developed as yard and ornamental veget ation, and would be considered developed beyond TOB. Observations of the creek conditions and habitats were also noted. TOB was recorded by flagging the TOB in the field and then surveying this line in using accurate survey methods.
City of San Mateo Municipal Code 7.39.130: WATERCOURSE PROTECTION applies to all watercourses, public and private, throughout the city (City of San Mateo 2024). Therefore, our setback analysis focused on the WATERCOURSE PROTECTION code and the City’s Slope Development Standards, which apply to creek banks.
In accordance with the City of San Mateo Municipal Code 7.39.130: WATERCOURSE PROTECTION, under Chapter 7.39: Stormwater Management and Discharge (City of San Mateo 2024):
“(a) Every person owning property through which a watercourse passes, or such person's lessee or tenant, shall keep and maintain that part of the watercourse within the property reasonably free of trash, debris, excessive vegetation, and other obstacles which would pollute, contaminate, or significantly retard the flow of water through the watercourse; shall maintain existing privately owned structures within or adjacent to a watercourse, so that such structures will not become a hazard to the use, function, or physical integrity of the watercourse; and shall not remove healthy bank vegetation beyond that actually necessary for said maintenance, nor remove said vegetation in such a manner as to increase the vulnerability of the watercourse to erosion.
3 [USACE] U.S. Army Corps of Engineers. 2008. A Field Guide to the Identification of the Ordinary High Water Mark (OHWM) in the Arid West Region of the Western United States: A Delineation Manual. ERDC/CRREL TR -08-12. 3 H. T. Harvey & Associates
(b) No person shall commit or cause to be committed any of the following acts, unless a written permit has first been obtained from the Director of Public Works:
… (3) Carry out development within 30 feet of the center line of any creek or 20 feet of the top of a bank; …or,
(6) Place any loose or unconsolidated material along the side of or within a watercourse or so close to the side as to cause a diversion of the flow, or to cause a probability of such material being carried away by stormwaters passing through such watercourse.”
City of San Mateo Slope Development Standards state that the slope setback distance is determined by a combination of slope steepness, slope height at top of slope, and/or a calculation of distance related to slope height and horizonal/vertical distance (City of San Mateo 1998). As per the Slope Development Standards:
“for a slope over 25% up to and including 50%, and 10 feet to 30 feet height top of slope, the setback from top of slope is the greater of either:
15 feet,
The diagonal distance of 3:1, 3 horizontal to 1 vertical measured from the toe slope, or, A distance equal to the slope height from the top of slope.”
In this case, we defined “toe slope” to be the bottom of the creek, which was approximated well by the current property line which is a stream centerline, and “top of slope” to be TOB.
We chose three points along the creek which each represent approximately 1/3 of the length of the creek, each with unique characteristics including ground cover and slope percent. Then, using an inclinometer, we measured degree of slope steepness from the toe of slope. Horizontal distance from toe of slope to top of slope/bank was measured using GPS. Finally, the depth from toe of slope to the bottom of the creek was visually estimated and trigonometric calculations, and verified using LIDAR topographic data (ESRI, 2024).
Results. The approximately 0.6-acre project parcel is located in the midst of urban-suburban development, 3.5 miles east of Crystal Springs and 4 miles west of the San Francisco Bay (Figure 1). The reach of the unnamed creek adjacent to the parcel is channelized and runs perpendicular to LaSalle Drive. The creek does not appear in maps from National Wetlands Inventory or U.S. Geological Survey, and is undergrounded in culverts and bridges both up- and down-stream of the project site. At the time of the October survey, there was low flow with about 3-6 inches of water. Since October is towards the end of the dry season, and the conditions were normal at the time of the survey, this unnamed creek is likely perennial (EPA 2024). 4 The creek channel is incised, likely due to
high flows during previous rainy seasons’ storm events. There is a three-foot-wide culvert at the west end of the unnamed creek, a chain-link fence near the midway point with a handmade structure that allows for water flow,
4 [EPA] Environmental Protection Agency. 2024. Antecedent Precipitation Tool [Software]. Available from https:// www.epa.gov/wotus/antecedent-precipitation-tool-apt.
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and an opening at the east end which drains under the road. The eastern drainage is piped underground after the road crossing. The low-flow channel is approximately 3 feet wide and has a sandy substrate filled with 3 -4 inch wide, gravelly rocks. The creek bottom is unvegetated, does not support wetlands, and tree roots stick out of the break in slope delimiting the low flow channel.
The mapped TOB line and riparian canopy and habitat are shown on Figure 2. The riparian area within the project parcel was determined by identifying trees rooted below or right at the top of bank on the 2033 LaSalle Drive side of the creek, and whose canopies overhung the creek substantially. Riparian habitat did not include any trees rooted beyond top of bank, even if they had continuous canopy cover with trees rooted below top of bank , as many of these appeared planted and did not have any biological relation to the stream, being located well above the stream’s water table or expected area of normal flooding . The riparian area within the parcel has an approximately 50% slope (2:1). The slopes are more gradual at the east and west extremities, and steepest in the middle. Overstory tree species included some natives such as coast live oak ( Quercus agrifolia) and cottonwood (Populus fremontii), as well as non-natives such as Japanese cheesewood (Pittosporum tobira), brush cherry (Syzygium paniculatum), silky oak (Grevillea robusta), and Peruvian pepper tree (Schinus molle). A planted coast redwood (Sequoia sempervirens) was rooted just above the edge of top of bank at the eastern reach and is not considered a part of the riparian drip line. This redwood is a part of a continuous row of landscaped yard trees that are planted in a flat, sandy landscaped area. Understory vegetation species included nightshade (Solanum sp.), smooth leaved elm (Ulmus minor), bitter lettuce ( Lactuca virosa), French broom (Genista monspessulana ), Himalayan blackberry ( Rubus armeniacus), bull thistle (Cirsium vulgare), nettleleaf goosefoot (Chenopodium murale), periwinkle (Vinca major), English ivy (Hedera helix), and stream orchid (Epipactis sp.), all of which were vegetative at the time of the survey.
Upland, developed habitat north of the riparian habitat was flat and entirely developed/landscaped, consisting of concrete driveway, ornamental species such as aloe ( Aloe sp.), or jade (Crassula sp.), turf grasses, and redwoods along the east edge of the parcel . Developed plantings occurred under the riparian dripline beyond TOB and would not be considered sensitive habitat at the ground level, even though the riparian canopy overhangs this area. Photos of the creek channel, riparian area, and adjacent upland are presented in Appendix B.
Stream/Slope Setback. Slope height was 10, 8.5, and 7 feet at data points 1, 2 and 3 respectively. The average vertical slope height at top of slope/bank was 8.5 feet. Therefore, the minimum slope setback for new buildings, as described in the Slope Development Standards, is 15 feet from TOB. This is greater than either the 3:1 distance from toe of slope or the distance of the depth from TOB.
The Watercourse Setback was evaluated as 20 feet from TOB, which was greater than 30 feet from toe of slope.
Figure 2 in Appendix A shows the results from the survey on October 30 , 2024, including TOB, stream centerline/toe of slope, dripline for the north bank riparian vegetation, and the slope and watercourse setbacks.
New buildings proposed by the project avoid both setbacks.
Riparian Impacts under CEQA. The proposed project associated with this riparian setback survey is anticipated to have less than significant impacts on the riparian area and no impacts on the creek itse lf. The 5 H. T. Harvey & Associates
proposed project will not be removing any riparian trees or trees within the riparian corridor, and has been designed to avoid all impacts to the creek, creek banks, and riparian corridor. Tree protection zones will be established around all trees to be preserved by the project , with arborist monitoring for work that must occur within these zones. Project activities are planned as replacement-in-kind within the existing developed footprint.
However, any development that may occur under the riparian canopy that overhangs the site will only affect the existing developed habitat, and will not introduce new buildings within this area. Within the developed area under the overhanging riparian canopy and adjacent to this area within the setback, existing landscaping will be updated for landscaping consistent with the requirements of the Early Childhood Center , such as garden nooks, a vegetable garden and sand and mud play areas. There would be no new hardscape under the riparian canopy and no increase in hardscape within the setback area from existing conditions.
Implementation of the proposed project could result in temporary impacts to the adjacent mixed riparian woodland habitat (i.e., trimming of riparian trees or minor impacts to roots ) as a result of construction in the landscaped urban-suburban strip along the riparian canopy edge (Figure 2), however these impacts are expected to be minor , would restore naturally after construction, and would not constitute a permanent reduction in riparian canopy. During construction, the riparian trees and the sensitive are as below TOB would be protected with appropriate Best Management Practices (BMPs), which may include fiber rolls and Environmentally Sensitive Area fencing. The project would not be expected to introduce additional human presence within the riparian habitat, as there are no plans for the Center to utilize, develop, or in any other way permanently impact the riparian habitat or creek. Given the existing levels of disturbance, the replacement of existing landscaping with new landscaping (thus not increasing hardscape within the developed area under the riparian canopy), the implementation of BMPs that will be utilized by the project to protect the sensitive riparian habitat and the stream, and the lack of any permanent disturbance to any sensitive riparian habitat or areas below TOB, and the full avoidance of both applicable City setbacks for the new building, the impacts to riparian habitats from the project would be considered less than significant.
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Appendix A. Figures
San Mateo
Park
Parr
ott Dr
Baywood Park
Highlands
Cypress Ave
S B St
Aragon Blv
d
Laurel Ave
N Ellswort
h Av
e
Norton
St
Barneson Ave
19t h Av e
Palm
Ave
WPopl
ar Ave
Bridge Rd
Notre Dame Ave
Upla nds
Dr
Tilton Ave
Oregon Ave
Sierr
a Dr
Elm
St
Avila Rd Lesl
ie
St
E 16t
h Av
e
E 3rd Av
e
W 3r
d
Ave
San Mateo
County
Fairgrounds
Aragon High
School
Nineteenth
Avenue Park
Downtown San
Mateo
Baywood
Beresford
Manor
East San
Mateo
Aragon
South
Shoreview
Hillsborough
Heights
Foothill Terrace
Baywood
Knolls
Sunnybrae
S an M at eo
92 Parr
ott
Dr
27th Ave
28th Ave
36th Ave
Edison St
42n d Ave
24th A
ve
To
urna
ment Dr
30th Ave
Asc en sion D
r
W Hi ll sdal e B lvd
Hillsdale
Shopping
Center
Laurelwood
Park
College of San
Mateo
Southwest
Hillsdale
College
Heights
Northeast
Hillsdale
Laurelwood
Country Club
Heights
Northwest
Hillsdale
Highlands-Baywood
Park
S N
orf
olk St
Saratoga Dr
Kehoe A ve
Eisenhower St
Parkside
Fiesta Gardens
Lyon
Ave
Ala
med
a
de
Las P ulg
as
Southeast
Hillsdale
Bay Meadows
San Mateo
Village
^_^_
^_
^_
^_
^_
^_
^_ ^_
^_
^_
^_
SACRAMENTO CALAVERAS
PLACER
MARIPOSA
TUOLUMNE
EL DORADO
SAN JOAQUIN
MERCEDSTANISLAUS
AMADOR
Auburn
Woodland
Placerville
Sacramento
Jackson
San Andreas
Stockton
Sonora
Modesto
Merced
N:\Projects4900\4907-01\Reports\Riparian Setback Assessment\Riparian Setback Assessment.aprx 2,000 0 2,0001,000
US Feet±
Figure 1. Vicinity Map
Project
Vicinity
California
Project Location
Carey School Riparian Setback Assessment (4907-01)
October 2025
La Salle Dr
Carey Elementary School
Background: NearMap Imagery (09/02/24)
N:\Projects4900\4907-01\Reports\Riparian Setback Assessment\Riparian Setback Assessment.aprx 40 0 4020
Feet
±
Project Parcel
Stream Centerline / Toe of Slope
Top of Bank
Slope Setback
Watercourse Setback
Riparian Canopy
Figure 2. Carey School Riparian Setback
Carey School Riparian Setback Assessment (4907-01)
October 2025
Carey School Ln
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Appendix B. Photo-documentation
Photo 1. Photo of developed habitat west of project site. Photo taken October 30, 2024, facing south.
Photo 2. Photo of bank stabilization along north bank at western end of project site. Photo taken October 30, 2024, facing east.
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H. T. Harvey & Associates
Photo 3. Chain-link fence and handmade water flow structure, obstructed by oleander (Nerium sp.). Photo taken October 30, 2024, facing southwest.
Photo 4. Representative photo of riparian habitat present adjacent to unnamed Creek. Photo taken October 30, 2024, facing east.
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Photo 5. Photo of redwood rooted above top of slope. Photo taken October 30, 2024, facing east.
Photo 6. Photo of planted redwoods (Sequoia sempervirens), with the redwood from Photo 5 at the end, in residential backyard.
Photo taken October 30, 2024, facing south.
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H. T. Harvey & Associates
Photo 7. Photo of encaged, 3-foot-wide culvert at east end of unnamed creek. Photo taken October 30, 2024, facing east.
Photo 8. Photo of 1-foot-wide storm drainage pipe extending out from the southern bank. Photo taken October 30, 2024, facing south.
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Photo 9. Photo of the water drainage at the western end of the creek.
Photo taken October 30, 2024, facing west.