Fulshear Master Drainage Plan

Phase 2 – South FM 1093 City Limits and ETJ

August 2021

Scope of Work• City of Fulshear city limits and ETJ is subject to varying flooding conditions

• Flooding from the Brazos River, major creeks, smaller local creeks, and undersized localized systems

• Identify regional and localized drainage improvements to reduce or eliminate flooding. Focus of the Phase 2

study was south of FM 1093

• Brazos River: evaluate traditional development floodplain reclamation and utilizing levee system to protect

against

• Major Riverine Flooding Sources: Review FBCDD preliminary models and analysis For Jones Creek and Bessie’s

Creek watershed. Incorporate any improvements as needed.

• Smaller Local Tributaries: Developed hydraulic models and determine proposed improvements to contain 100-

year runoff. Developed alignments, channel design parameters, right-of-way widths, and general development

requirements (detention needs) for each system.

• Minor Local Drainage Systems: Evaluate localized areas along and within the vicinity of the Bois D Arc area.

Determine outfall locations and evaluate need drainage improvements for the 100-year runoff.

• Develop long term regional projects and short-term (5 years or less) CIP projects within the context of the

overall regional projects

Overall Watershed Boundaries

• Utilized the FBCDD major

watershed boundaries

• City limit and ETJ is within three of

the watersheds.

• These boundaries held to develop

more localized sub-basin

delineations.

Watershed Boundaries – Phase 2

• Overall watershed boundaries sub-

divided utilizing the FBC LiDAR

Dataset

• Sub-basins utilized to develop

hydrologic computations of runoff

for hydraulic evaluations.

• Sub-basins were delineated for

areas draining directly to the Brazos

River

Brazos River FloodplainFBCDD preliminary 100-YR floodplain

Approximately 9,600 acres of Fulshear ETJ within the floodplain

Floodplain reclamation done using two methods:

1) Traditional floodplain fill which includes only raising the specific areas being developed

2) Levee which maintains natural grounds but protects around a large area

Brazos River – FEMA and Preliminary FBCDD Comparison

• FEMA floodplain generally matches

extents of FBCDD preliminary

floodplain

• FBCDD better identifies backwater

flooding up Bessie's Creek

• FBCDD models demonstrates ability

for floodwaters to overtop Bois

D’Arc and flow east along Jones

Creek and Flewellen Tributary

Brazos River – Development Requirements

• Lowest Fill Elevation at the Base

Flood Elevation for the Location

• Example – BFE at 96, then minimum Fill

at 96

• FBCDD Requires Slab Elevations +2

feet above the Brazos 100-year

• Example – BFE = 96, Minimum Slab = 98

• A Letter of Map Revision (LOMR)

Application be filled with FEMA to

remove from floodplain maps

• FBCDD requires a conveyance

analysis showing the proposed fill

does not create an adverse impact

Brazos River – Traditional Development

• Consider a Range of Fill Depths

• Over 4-feet of fill determined to

be above traditional construction

techniques for standard

development.

• Consider large lot development in

which only the House Slab is

raised above the 100-year (issues

with roads and emergency access

during River Floodplain Events)

Depth of Fill Area Reclaimed Volume of Fill

(ft) (acres) (acre-feet)

3 3,992 5,499 $44,000,000

4 4,543 7,848 $63,000,000

5 5,617 12,002 $97,000,000

6 6,715 18,076 $146,000,000

Estimated Construction

Cost

Brazos River – Ring Levee

• Protected Area = 3,700 acres

• 80,000 LF of levee ranging from 4-feet to 14-feet in height

• FBCDD requires a conveyance analysis showing the levee in place with no water surface increases.

• Mitigation ponds (which can be used for recreational facilities) to mitigate the floodplain fill impacts

• Internal drainage system requiring pump station

• Developer driven project. No benefit to existing City limits

Brazos River – Regional Levee

• Protected Area = 7,000 acres

• 62,700 LF of Levee Ranging from 4-

feet to 14-feet in height

• Estimated Cost at $60MM

• FBCDD requires a conveyance

analysis showing the levee in place

with no water surface increases.

• Mitigation ponds (which can be

used for recreational facilities) to

mitigate the floodplain fill impacts

• Internal drainage system requiring

pump station

• Benefits to Red Bird, Bois D’Arc, and

Lea/Penn

Brazos River – Alternative Comparisons

Alternative Cost Estimate Pros Cons

Traditional Development

$63 MM

4,500 acres of reclaimed land

• Follows standard development practices. • Homes are constructed above the Brazos 100-year

and do not depend on Levee• No pump stations required

• Greatly limits the amount of future developable land

• No benefit to City limits or region• Mass fill required for developments

Ring Levee $48 MM

3,700 acre of reclaimed land

• No direct involvement or cost to city. Developer driven.

• Provides protection for majority of remaining ETJ land.

• Only protects for new development. • No benefits to City limits.

Regional Levee $60 MM

7,000 acres of reclaimed land

• Provides highest leave of flood protection for region

• Lower cost per acre reclaimed from floodplain• Allows for significant improvement in Red Bird

access Issues during flooding events• Allows for implementation of channel

improvements to reduce the Flewellen Tributary and Upper Jones Creek flooding issues (Lea/Penn and Bois D’Arc)

• Difficult to implement• Requires extensive coordination

with landowners and county• Right-of-way/easement acquisition

required

Brazos River – Regional Levee Phase 1• Protects areas within the City limits

• 62,700 LF of levee ranging from 4-

feet to 14-feet in height

• Backwater floodplain so limited

mitigation needs

• No major outfalls requiring pump

stations until development

commences

• Large gravity structure for levee

required at Outfall into Bessie's

Creek

• Benefits to Red Bird, Bois D’Arc, and

Lea/Penn

• Estimated total cost of $8.1MM

Brazos River – Recommended Alternatives

• Regional levee provides the highest level of flood protection for the City limits

• Regional levee can be phased from upstream to downstream

• Allows for long-term improvement of flooding conditions within the Bois D’Arc area

• Can be done independently of the either the Ring Levee option or extension of regional levee

• Phase 2 Levee and construction of Phase 1 Levee coordinated with development of the Winner-Foster properties

• Recommend City to develop a Preliminary Engineering Report of the Phase 1 Levee and pursue setting a final levee alignment followed by right-of-way/easement acquisition (GCWA pump station to upstream tie in location.)

• Approximate PER cost = $75,000

• ROW acquisition estimated at 48 acres at $2MM

• Phase 1 construction and engineering estimated at $6,100,000

Riverine Systems

• The City Limits and ETJ are within two major watersheds:

1) Bessie’s Creek

2) Jones/Flewellen Creek

• Fort Bend County Drainage District has released draft versions of floodplain and improvement studies for both watersheds.

• The MDP considered both of these systems per the results of that study.

Bessie’s Creek• Preliminary FBCDD results shows

little out of bank floodplain due to

Bessie’s Creek downstream of James

Lane

• FBCDD evaluated regional detention

and channel improvement options

along Bessie's, with little to no

benefit for existing properties

downstream of James Lane

• Detention downstream of FM 1093

may note beneficial due to the

hydrologic watershed response

• FBCDD is further developing criteria

for these development conditions,

recommend following FBCDD

guidance

Jones/Flewellen Creek• Preliminary FBCDD results shows

significant out of bank flooding

along Flewellen and the Tributary

• Any development will need

floodplain fill mitigation and

detention volume

• Lack of downstream channel

capacity in Jones and Flewellen

limit ability to improve flooding

conditions.

• Diversion of flows from Flewellen

and Jones considered by FBCDD

generally around FM 723

• Diversion of Flewellen Tributary

and Oxbow Lakes along Jones

Creek considered in this analysis.

(See Below)

Localized Riverine Systems

• Larger engineered riverine systems such as development channels, detention ponds, outfall channels, etc..

• Drainage areas generally between 1 to 5 square mile

• System evaluated and sized for the Atlas 14 100-year storm event.

• Onsite detention required for developments so as to not impact the peak water surface elevations along the systems

• Design parameters include:

• Minimum channel bottom width: 6-ft

• Side slopes at 4:1

• Maintenance berms at 30-ft, with 15 in commercial areas

• Channel depths range from 10 to 15-feet

Fulshear Lake System

• Design Atlas 14 model for FMUD1 utilized as a base condition

• This model considers land north of FM 1093 and Huggins Drive to

the outfall into Bessie’s Creek.

• This model has Fulshear Lake included as a storage node

• Development upstream of FM 1093 will require detention to not

impact the FM 1093 culvert crossings

• Development downstream of FM 1093 can be developed without

detention with an additional 10x8 RCB at downstream Fulshear

Trace road crossing and an additional 10x8 RCB drop structure into

Bessie’s Creek.

• Fulshear Lake requires mitigation for any fill below elevation 104.5

(Atlas 14 100-year)

• Improvements to performed and funded by future developers.

• In lieu of downstream improvements, onsite detention would be

needed to not impact the Fulshear Lake system

1-10x8

1-10x8

Brazos Tributary Channels• Tributary 1 – 11,400 LF proposed

channel excavation, 200-foot ROW

width, at estimated cost $4.4 MM

including crossing

• Tributary 2 – 21,800 LF proposed

channel excavation, 220-foot ROW

width, at estimated cost $9.5 MM

including crossing

• Tributary 3 – 12,500 LF proposed

channel excavation and alignment

extension, 200-foot ROW width, at

estimated cost $4.8 MM including

crossing

• Large culvert crossings required

• Developer driven Improvements (No

City Funds)

FMUD2/Bois D’Arc Outfall Channel

• 1,200 LF of 5x4 box culvert

estimated at $600,000

• In the interim, a 100-foot-wide

ROW temporary channel to

convey flows

Lea/Penn Outfall Channel

• Ultimate channel to divert flow from

Flewellen Creek directly to Brazos River

• Will require the regional levee so as to

prevent backflow from the Brazos

• Design bottom width of 60-ft with a

channel right-of-way of 240-feet

• Development will be required to

provide a minimum of 0.4 acre-feet per

acre of detention

• Allows for lowering of internal

floodplain along Flewellen Tributary for

both future development and for

existing properties along Lea/Penn and

Bois D Arc.

• Estimated construction cost $13.9 MM

for channel and bridge

Lea/Penn Outfall Channel – Phase 1• Initial Phase of Channel to Jones

Creek Oxbow ponds

• Can be constructed now while

the larger improvements are

developed

• Utilize City Land at end of Penn

to drain to Channel

• Channel provides both depth and

capacity to allow for collection of

internal improvements along Lea

and Penn.

• Phase 1 Channel and Culverts

estimated cost $814,000

Minor Systems

• Localized Drainage Systems generally below 200 acres in size

• Utilize small channels, storm sewer, or roadside ditches

• Helps improve more frequent storm event and ponding seen

• Lower Bois D Arc area subject to lack of topographic relief and undersized outfall structures.

• Localized Drainage Areas based on existing outfall locations and peak flows computed

• Outfalls Sized for the 100-year storm event

Minor Outfalls

• B-1: 1,300 LF of 10x5 Box

Culvert estimated at $1.5MM

• B-2: Roadside Ditch

Improvements Only estimated

at $150,000

• C-1 (Walker Lane): 600 LF of

42” RCP estimated at $280,000

• C-2 (Walker Lane): 300 LF of 2-

60” RCP and 1,500 LF of 140-ft

easement channel estimated

at $600,000.

Minor Outfalls

• B-3: 900 LF of 1-9x5 RCB

estimated at $900,000

• B-4: 815 LF of 1-60” RCP

estimated at $408,000

Conclusions and Recommendations

• Utilize results of the MDP-Phase 2 to guide development requirements and improvement needs for each system. This includes detention requirements, floodplain mitigation, easement dedication, and outfall locations.

• Incorporate Projects into 5-year CIP plan for City

• Take Questions from Staff and Council and make any final modifications to results and improvements to the Phase 2 MDP

• Initiate the Phase 3 MDP focused on the west and north portions of the City limits and ETJ

Proposed CIP Projects (5 years and Less)

Project Description TYPE Cost

Master Draiange Plan - Phase 3 Study $125,000.00

Brazos Levee Phase 1 PER Study $75,000.00

Brazos Levee Phase 1 ROW/Easement Aqusition ROW $2,000,000.00

Brazos River Levee Phase 1 Engineering and Construction Construction $6,100,000.00

FMUD2/Bois D Arc Outfall Improvements Construction $600,000.00

Lea/Penn Outfall Channel - Phase 1 Construction $814,000.00

Bois D Arc Drainage Improvements Segment B-1 (10x5 RCB) Construction $1,500,000.00

Bois D Arc Drainage Improvements Segment B-2 (Roadside Ditch Improvemetns)Construction $150,000.00

Bois D Arc Drainage Improvements Segment B-3 (9x5 RCB) Construction $900,000.00

Bois D Arc Draiange Improvements Segment B-4 (60" RCP) Construction $408,000.00

Walker Land Drainage Improvements C-1 (42" RCP) Construction $280,000.00

Walker Land Drainage Improvements C-2 (2-60" RCP and Channel) Construction $600,000.00