The Greenway crossing now being planned at Waipuilani Gulch is not just a pedestrian or collector-road feature. It is a flood conveyance decision. If that crossing is undersized, narrowed, or treated like a simple trail bridge, it will become another choke point in a system that already fails under heavy rain.
This page focuses on what needs to be built at the Greenway and why the crossing must be sized for full restored flow. For the broader background on how this flood system already behaves from Piʻilani Highway to South Kihei Road and the coast, see Waipuilani Gulch Flooding Issues.
Zone 1: The Greenway Crossing Must Be Built for Full Flow
The first and most immediate issue is the proposed Greenway bridge itself. This is where the public can still influence the design before a bad crossing is built and paved into place. A small bridge, a culverted causeway, or any narrowed opening would be a long-term failure. The crossing must preserve the width of the gulch, allow debris passage, and avoid creating a higher-velocity pinch point in the lower channel.
This matters even more because the Greenway will not exist in isolation. Once paved, it will generate its own stormwater. The surrounding neighborhoods on both sides also send runoff toward the same drainage system. That means the crossing is not merely carrying an existing path over a gulch. It is becoming part of a larger hardscape and urban runoff system that adds pressure to a flood corridor already known to fail.
For the established flooding background behind this concern, including the behavior of the wider watershed and downstream constrictions, see Waipuilani Gulch Flooding Issues.
The minimum standard should be simple: the crossing must be designed for full restored flow in the main channel, not reduced flow assumptions based on present-day diversions or temporary berming. The gulch should remain as wide as possible for as far as possible. Narrowing the active flood corridor increases velocity, raises blockage risk, and makes downstream overflow more dangerous once the next restriction is reached.
What Is Currently Planned
Public planning documents already confirm that this North-South Collector Road segment is moving forward. The Kihei Community Association described the segment running from Waipuilani Road to Kulanihakoi Street as part of the next extension, with construction long delayed but tied to the same Greenway corridor now under discussion. Maui MPO transportation documents likewise state that this phase will extend an existing 2-lane roadway and separated multi-use path from Kulanihakoi Street to Waipuilani Place and construct a bridge over Waipuilani Gulch.
What those public references do not clearly disclose is just as important. They do not tell the public how wide that bridge will be, whether it will preserve the full width of the gulch, what hydraulic standard it will be built to, or whether it is being designed as a true open-span flood conveyance structure rather than a narrower cost-controlled crossing. That missing detail matters. A bridge can be publicly listed in a project scope and still be too small for the real flood conditions it will face.
That is why the Greenway bridge should not be judged merely by whether a bridge is included at all. The real question is whether the crossing is being designed to preserve full conveyance, accommodate debris, and avoid creating another constriction point in a gulch that already fails downstream. Until those design details are public, the community has every reason to insist on minimum specifications that match the actual flood function of Waipuilani Gulch.
The concept bridge shown above is SaveKihei.org’s proposal for the kind of full-width flood conveyance structure that should be built. It is shown precisely because the official project descriptions do not yet disclose enough design detail for the public to know whether the actual crossing will be sized correctly or engineered as a cheaper, narrower, and more expedient structure.
For more background on this delayed NSCR / Greenway segment and the need for safer mauka-makai connections, see NSCR construction date now two years later: 2024 for next segment.
For the official project overview, see Liloa Drive Extension Project.
Zone 2: The Liloa / Ho‘onani Dirt Berm Diversion Distorts the Current Flow Pattern
The second issue is the unofficial dirt berm and altered flow pattern near Liloa Street and the Ho‘onani area. For years, part of the Waipuilani flow has been redirected north by earthen berming and roadway grading rather than continuing fully down the main channel. That diversion altered how floodwater moved across the area and created the false appearance that the lower main channel could carry less water than it should actually be designed for.
This is one of the reasons the Greenway crossing cannot be designed around the current distorted conditions. The diversion reduces apparent flow in the main channel, but it is unstable and cannot be used as a design assumption.
Waipuilani Gulch has an illegal stream diversion that diverts floodwater north to the Waiohuli StreamThe berm itself was never a reliable solution. It was an informal manipulation of flow in a place where floodwaters need room. During major storm conditions, temporary or unofficial diversions can fail and release more flow back into the main channel. That is exactly why future planning cannot assume reduced flow in Waipuilani Gulch. Any Greenway crossing must be sized for the condition that ultimately matters most: full flow remaining in the main gulch.
For more on the broader downstream flooding pattern created by constrictions and altered flow, see Waipuilani Gulch Flooding Issues.
Zone 3: South Kihei Road Is the Known Downstream Choke Point
The third issue is the downstream bottleneck at South Kihei Road. This is where one of the most severe restrictions in the system already exists. At that crossing, Waipuilani has long been forced through a very limited outlet that clogs quickly with debris and sediment. Once blocked, water overtops, spreads north, floods nearby neighborhoods, closes South Kihei Road, and leaves behind mud and extensive cleanup.
The downstream flooding behavior at South Kihei Road is already documented in Waipuilani Gulch Flooding Issues. The purpose of this page is not to repeat that full explanation, but to connect it directly to the new Greenway crossing now being planned upstream.
This is the key downstream warning. Increasing capacity at the Greenway without addressing the restriction at South Kihei Road does not solve flooding. It simply moves more water, more debris, and more sediment into the next choke point faster. That can make downstream failure worse, not better.
One Gulch, Three Linked Failures
These are three distinct issues, but they are not separate problems. They are one connected system. The Greenway bridge is the most immediate design decision. The Liloa / Ho‘onani dirt berm diversion is a distorted interim condition that should not be treated as normal. South Kihei Road remains the known downstream choke point. Each one affects the others.
That is why the Greenway crossing has to be built to a higher standard from the beginning. It should be sized for full restored flow in the main channel. It should preserve the width of the gulch rather than constrict it. It should allow debris passage. And it should be evaluated in the context of the downstream South Kihei Road bottleneck and the wider wetland system below.
For the established background page that documents the existing flooding behavior and failure pattern at Waipuilani Gulch, see Waipuilani Gulch Flooding Issues.
Waipuilani Gulch already shows what happens when capacity is underestimated and flow paths are misunderstood. The Greenway crossing is an opportunity to correct that or to repeat it. Anything less is not resilience. It is another avoidable failure being built in advance.
Proposed Improvements to the South Kihei Road Constriction
The most critical downstream failure point in the Waipuilani Gulch system remains the South Kihei Road crossing. The existing conveyance is severely undersized relative to actual flood conditions and acts as a hard choke point that backs water into upstream neighborhoods and forces overflow into surrounding residential areas.
According to the Ecological Alternatives Analysis, the current culvert at South Kihei Road is approximately 10 feet by 2 feet, with a capacity of less than 200 cubic feet per second. In contrast, estimated 100-year storm flows moving through this system are on the order of 8,000+ cubic feet per second. That is not a marginal deficiency. It is a system failure by more than an order of magnitude.
The diagram above illustrates a realistic and constructible solution: expanding conveyance not only at the road crossing, but through the entire constrained corridor immediately makai of South Kihei Road, including beneath the Kauhale Makai and Luana Kai condominium frontage areas.
This concept aligns directly with alternatives identified in the Amanda Cording report, which evaluated multiple solutions including large-span bridges, extended box culverts, and culvert systems routed beneath developed areas. One of the key alternatives specifically includes multiple large box culverts beneath condominium parking areas, with temporary excavation and restoration of parking surfaces after construction.
This is critical: meaningful improvements at this location are not possible without addressing the entire constrained frontage zone. Simply enlarging the road crossing alone will not solve the problem if the downstream corridor remains restricted.
Minimum Required Capacity (South Kihei Road Crossing)
Any viable solution must be designed around actual hydraulic requirements, not convenience or cost minimization.
Based on the Ecological Alternatives Analysis and Kihei Drainage Master Plan assumptions, the following minimum performance criteria apply:
- Target Flow Capacity: approximately 8,000 to 10,000 cubic feet per second
- Equivalent Opening Width: approximately 40 to 70 feet minimum
- Vertical Clearance: approximately 6 to 8 feet minimum, with greater clearance preferred for debris passage
- Flood Elevation Accommodation: system must safely pass major storm flows without recreating the existing choke point
- Debris Passage Requirement: must allow large debris transport without immediate clogging
The Amanda Cording report outlines multiple solution types at this scale, including a roughly 70-foot bridge crossing, multiple large box culverts, extended culvert corridors running hundreds of feet through constrained zones, and supplemental culverts beneath condominium parking areas. These are not theoretical upgrades. They are the minimum scale of intervention suggested by the modeled flood conditions.
Integrated Corridor Solution (Not a Single Fix)
The South Kihei Road crossing cannot be treated as an isolated structure. It is part of a continuous hydraulic system that includes the upstream gulch flow entering from mauka, the road crossing itself, the constrained corridor between condominium properties, and the downstream discharge through Waipuilani Park to the ocean.
If any one segment remains undersized, the entire system fails.
This is why the concept shown above extends beyond the road crossing itself. It proposes large-span culverts beneath Kauhale Makai parking areas, potential expansion toward the Luana Kai frontage where space allows, and full corridor conveyance continuity from mauka to makai.
Importantly, this approach does not require permanent loss of parking. Construction can be phased so that parking areas are temporarily removed, culverts installed below grade, and parking restored above. This is the only realistic way to provide full outlet capacity while still preserving long-term use of the condominium properties.
Why Smaller Solutions Will Fail
Any attempt to install undersized culverts, partial upgrades, or “good enough” infrastructure at South Kihei Road will simply recreate the same flooding conditions seen today.
The physics of the system are not negotiable. Water will move downhill from mauka to makai. If blocked, it will spread laterally into neighborhoods. If restricted, it will rise until it overtops barriers.
The existing system already demonstrates these failure modes during major storm events. Without a full-capacity solution at South Kihei Road, improvements upstream — including the proposed Greenway bridge — will only accelerate water delivery into an unchanged bottleneck.
System Connection: Mauka to Makai
This downstream constraint is directly connected to all upstream issues discussed in this article, including the proposed Waipuilani Gulch Greenway Bridge, the illegal diversion and berm impacts in the Ho‘onani / Liloa area, and the cumulative stormwater inputs from surrounding developments.
These are not separate problems. They are parts of a single hydraulic system.
For full upstream and system-wide context, including how this relates to the Greenway bridge and Liloa diversion, see Waipuilani Gulch Flooding Issues.
Related Analysis and Background
Waipuilani Gulch Flooding Issues
Extreme Flooding in Kihei – March 2026 Stormwater Failure
Impacts to the Watershed of the North-South Collector Road, Kihei
NSCR construction date now two years later: 2024 for next segment
Liloa Drive Extension Project
Ecological Alternatives Analysis (Amanda Cording)