ObjectivesThe Kinnickinnic River (KKR) watershed and its mainstem andtributary channels have undergone significant man-inducedchanges since the 1830’s (Figure 1). These include:

� Urbanization of about 97 percent of the watershed;� Conversion of hardwood forests to farmland (1858-1870);� Drainage of the valley-bottom marshes ;� Elimination of riparian vegetation;� Construction of small dams and reservoirs on some of the

tributaries;� Channelization, straightening, concrete lining (38 percent; 9.6

miles) and enclosure (25 percent; 6.4 miles) of watershedchannels (Figure 2); and

� Installation of infrastructure (bed and bank protectionstructures as well as bridges and culverts) (Figure 3).

Figure 1. Kinnickinnic River Watershed showing the location of themainstem and major tributaries.

The urbanization resulted in an approximately 10-fold increase inthe magnitude of the peak flows. Much of the existing concretelining (installed between the late 1950’s and early 1970’s) is agedand deteriorating (Figure 4) and the channels no longer convey thedesign flows. The Milwaukee Metropolitan Sewerage District(MMSD) is exploring options for removing the concrete andrehabilitating the channels. MMSD’s goals include improvedaquatic and riparian habitat and enhanced recreationalopportunities while providing increased public safety and reducedimpacts from flooding. In the channels that are not concrete-lined,MMSD is concerned with bank erosion (Figure 5) and verticaldowncutting, as well as resulting sedimentation in the LakeMichigan estuary.

An extensive field reconnaissance was carried to evaluate theexisting morphology of the unlined channels, assess the conditionof the channel infrastructure, identify geomorphic and hydrauliccontrols, and characterize the channel boundary materials (Figure6). During the field reconnaissance, areas exhibiting bed or bankerosion were mapped to identify potential sites for rehabilitation.Representative cross sections were surveyed as part of the thisstudy to facilitate development of the hydraulic model.

The objective of the study conducted by Tetra Tech was to providea supplementary planning tool for flood management, channelstabilization, and rehabilitation activities within the KKR watershed,primarily within MMSD’s jurisdiction. Specific objectives included:

� Collecting and evaluating relevant sediment and geomorphicdata in the context of channel stability, flood management, andoverall watershed management;

� Identifying existing problem areas and opportunities forimprovement of watershed condition, to be integrated with floodmanagement initiatives;

� Providing a comprehensive database of geomorphic andsediment-transport characteristics to enable effective watershedmanagement and decision making;

� Providing guidance and prioritization of identified projects withinMMSD jurisdiction.

Kinnickinnic River: Rehabilitation in an Urban WatershedStuart C. Trabant, Michael D. Harvey, Robert A. Mussetter (Tetra Tech, Inc.),

David Fowler (Milwaukee Metropolitan Sewerage District)

The Issues Analytical Methods (cont.) Analytical Methods (cont.) Rehabilitation Opportunities (cont.)

For purposes of this analysis, the KKR and its tributaries weredivided into 47 subreaches. Reach-averaged hydraulics from theHEC-RAS model and bed material gradations for the individualsubreaches were used to conduct a sediment continuity analysis ofthe KKR for existing and future conditions. The results indicate thatthe most significant erosion will occur in the unlined reaches of theKKR and Lyons Park Creek, and that aggradation in the linedreaches is unlikely (Figure 9).

Analytical Methods

Figure 6. Bed material gradation curves for the 10 bulk samplesand 4 pebble counts collected along the KKR, and therepresentative curves for each subreach.

Figure 10. Conceptual design for the replaced channel in the Kinnickinnic River.

Field Reconnaissance

Sediment-transport

Figure 5. Bank erosion in the unlined portion of the KKR.

Figure 4. Damaged concrete lining in Holmes Avenue Creek.

USGS gage information was used in conjunction with HSPFhydrologic modeling to assess the more frequently occurring flowsthat will be the basis for the design of the rehabilitated low flowchannels and the extreme flood events that are the basis for thedesign of the overall flood conveyance channels under existingand future (2020 planned land use) conditions. The existingconditions analyses indicate that 10 percent mean daily flowexceedence level ranges from about 4.4 cfs in the upstreamportion of the KKR to about 48 cfs at the downstream limit of thestudy reach, while the 100-year peak flow ranges from 1,960 cfs to8,050 cfs at these two locations (Figure 7).

Hydrology

HEC-RAS modeling was used to identify the channel capacityalong the KKR (Figure 8), and to provide input to the sediment-transport analysis. The HEC-RAS model was initially developed bythe Southeast Wisconsin Regional Planning Committee(SWERPC), and was updated for this study using the most recenttopographic mapping and survey data. In the unlined portions ofthe KKR, the channel capacity ranges from the 2- to 10-yr RI peakflows. In the concrete-lined portions of the KKR, the channelcapacity is generally greater than the 100-yr RI peak flow, except inareas that are affected by localized backwater zones created bybridges and in one reach with heavy residential encroachmentwhere the channel capacity is less than the 25-yr RI peak flow.

Hydraulics

Rehabilitation OpportunitiesThe primary problems identified within the KKR and tributaries bythis study and the identified opportunities for rehabilitation are:

• Problem: Lack of hydraulic capacity (<100-year peak flow),primarily in the concrete-lined subreaches of the KKR betweenSouth 43rd Street and South 6th Avenue.

� Rehabilitation Opportunity: Replacement of the existing,concrete-lined channel with a larger channel geometry toprovide increased flood conveyance. Successful replacementcould be achieved with a compound channel, sized to conveythe 100-yr RI design flow without eroding, including a low-flow,rock-lined channel sized to convey about the 0.1-percent meandaily exceedence flow (Figures 10 and 11). Appropriate verticaland lateral variability could be incorporated to provide fishpassage and resting areas.

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Figure 8. Channel capacity evaluation in the KKR.

Figure 7. Flood frequency curve at the S. 11th Street

Gage.

Figure 9. Results of the sediment-continuity analysis in Lyons Park Creek and the KKR.

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• Problem: Failed and poor-condition, open-channel concretelining, primarily in the KKR that was constructed in the early1960s and is coincident with the impaired hydraulic capacity.

� Rehabilitation Opportunity: Given the coincidence betweenthe poor state of the concrete and the impaired hydrauliccapacity, the compound channel identified to mitigate problemswith channel capacity would also remedy the problems with theconcrete lining.

• Problem: Eroding unlined channel segments in the KKR andtributaries that both threaten streamside infrastructure andsupply sediment to the downstream estuary of the KKR where itis deposited.

� Rehabilitation Opportunity: Stabilization of the eroding banksthat are currently threatening infrastructure could be achievedby installing a rock toe designed to withstand movement at the100-yr RI flow with bio-engineered upper banks (Figure 12).Rock riffle grade control structures will be necessary in areas ofdowncutting, and will also enhance habitat (Figure 13).

Figure 11. Photgraph of the existing KKR and conceptual rendering of the rehabilitated channel.

• Problem: Sedimentation in the Lake Michigan estuary.� Rehabilitation Opportunity: Stabilization of the currently

eroding banks and installation of grade control structures wouldreduce sediment loads delivered to the estuary by about 50percent.

Figure 12. Conceptual design of combination rock-toe and bio-engineered bank stabilization.

Figure 13. Conceptual design of rock riffle grade control structure.

Figure 3. 1960 photograph of riprap along the KKR.

Figure 2. 1961 photograph of the recently lined KKR.