The TMDL Sub-Basins

To better understand the Kane`ohe watershed, the __ square-mile ( acre; ha) basin is divided into five hydrologic units termed sub-basins. Each sub-basin is, in effect, a small watershed acting as a point source to Kane`ohe Stream, or in some cases, from one reach of the stream to a lower one. The sub-basin boundaries are determined from topography and known constructed drainageways that may alter the normal path of runoff. Sub-basins are chosen, in most cases, as that part of the watershed above a particular water quality station. In that way, the quality and quantity of discharge from a particular sub-basin can be attributed to data obtained at the WQ station.

Sub-basin 1: Kamo`oali`i Stream
This -acre portion of the Kane`ohe watershed encompasses most, but not all of the headwater streams that contribute to the flow of Kane`ohe Stream. All of Kamo`oali`i Stream above Ho`omaluhia Reservoir or Loko Waimaluhia is included. Outflow from this sub-basin is represented by TMDL Sta. 1a at the base of the reservoir dam. Other TMDL stations (1b through 1j) provide information on water quality of the many tributaries above the reservoir, with TMDL Sta. 1c representing Kamo`oali`i Stream at a point just before it flows into the reservoir.

face of the pali (photo by Eric Guinther)

Photo 1
Windward face of the pali showing uluhe fern dominating a colluvial deposit in the foreground and strong fluting of the cliff face by intermittent water flows in the background. The top of the cliff is less than half way up the mountain.

Within this sub-basin is the spectacular face the Nu`uanu Pali (cliff), down which flow numerous named and unnamed streams tributary to Kamo`oali`i Stream. These slopes are high (over 2000 feet or 600 m, rising to Pu`u Lanihulu in this sub-basin at 2700 ft or 820 m), steep, and rocky. Near vertical faces are fluted (Photo 1) by the slow erosion of multiple small waterfalls that only develop temporarily during periods of rainfall. Rainfall amounts average greater than 100 inches per year along this part of the Ko`olau crest. At the base of the rocky face occur steep colluvialA deposits supporting dense growths of trees or monotypic stands of uluhe fern (Dicranopteris linearis). While many species of plants occur in the forested areas, trees particularly common here are common guava (Psidium guajava), mango (Mangifera indica), silky oak (Grevillea robusta), Molucca albizia (Paraserianthus falcataria), African tulip (Spathodea campanulata), and kukui (Aleurites moluccana). In places, native pandanus (Pandanus tectorius), `ohi`a (Metrosideros polymorpha) and koa (Acacia koa) are still to be found. The steeper, higher slopes support grasses and shrub growth, regularly watered by cloud drip.

Photo 2
Golf cart bridge over Kamo`oali`i Stream at Koolau Golf Course just downstream from TMDL Station 1f.

Perennial flows develop in the streams at elevations between 600 and 800 feet above sea level, from small springs in the rocky colluvium. Flows build rapidly downslope over beds of water rounded stones and boulders. Much of this sub-basin is undeveloped, but below about 500 ft elevation, substantial land area is devoted to two golf courses, the H-3 Freeway right-of-way, banana plantations, windward campus of Hawaii Pacific University (HPU), and Ho`omaluhia Botanical Garden. Portions of four major windward O`ahu highways: Kamehameha, Pali, Likelike, and H-3, occur in this Sub-basin. On the slopes above the north side of Loko Waimaluhia occur residential neighborhoods of Kaneohe town. Thus, while a majority of this sub-basin is "undeveloped," in fact developments occupy substantial portions of the watershed -- it is just that these developments have low densities of roads and structures, as planned in an attempt to preserve the view from the famous Pali Lookout.

Within Ho`omaluhia Botanical Garden, stream riparian zones and slopes near the streams are well vegetated. Slopes around park roads tend to be well-maintained. Elsewhere in this watershed, stream flow may occur in natural beds with dense vegetation (Photo 2; as at Koolau Golf Course), or through lined or unlined ditches (as at the freeway interchange and along Old Pali Road.

Sub-basin 2: Luluku Stream
This sub-basin occupies only _ acres and is similar in most respects to Sub-basin 1 but encompassing only one tributary of Kamo`oali`i Stream: Lukuku Stream. This tributary differs from the numerous other small branches in Sub-basin 1 by the fact that Luluku joins Kamo`oali`i downstream of Loko Waimaluhia (reservoir). The highest point in this Sub-basin is the top of the pali (cliff) forming the windward face of Ko`olau mountain, here Pu`u Keahiakahoe at 2820 ft (860 m). The cliff face descends steeply, in some places vertically, to around 800 ft (240 m) and stream flow down this face is intermittent. Below the cliff occur aprons of debris eroded from the mountain (called colluviumA). These are steep near the top, but gradually tail out into an area of banana plantations on either side of Likelike Highway. The H-3 Freeway crosses this sub-basin, below which is a portion of Ho`omaluhia Botanical Garden.

Vegetation is as described for the upper parts of Sub-basin 1, with a concentration of banana plants (Musa x paradisiaca) on the slopes above and below the two major highways: Likelike and H-3 freeway. These plants are part of a commercial banana plantation.

TMDL Sta. 2 was located near the bottom of Luluku Stream where it crosses the park road at Ho`omaluhia Botanical Garden. This station represents the discharge from Sub-basin 2. This same location is the site of a USGS gaging station (now inactive) and a USGS NAWQA water quality station.

Sub-basin 3: Kamo`oali`i Lower Reach
Sub-basin 3 comprises the lower portion of Kamo`oali`i Stream between the Ho`omaluhia reservoir dam and the confluence with Kapunahala Stream. The stream channel is highly modified, in some areas consisting of box culvert (as beneath Likelike Highway) or concrete-lined channel, but mostly having a "natural" bed and modified banks as shown in Photo 4 taken in the area of the DOH bioassessment station.

Photo 3
Outflow from Ho`omaluhia reservoir (far left; from sub-basin 1) is joined with the flow from Luluku Stream (concrete culvert below house; bottom of sub-basin 2) and continues downslope (far right) as lower Kamo`oali`i Stream in sub-basin 3.

Kamo`oali`i Stream; City & County maintenance crew

Photo 4
Kamo`oali`i Stream is confined between wide, graded and in most places, concrete or concrete-rock masonry (crm), walls. Weedy growth is kept in check by regular herbicide spraying.

This entire reach of Kamo`oali`i Stream receives run-off through numerous street drains as it passes through the Kaneohe neigborhood of Keapuka. Water quality was monitored at TMDL Station 3a located at the lower end of the sub-basin.

Sub-basin 4: Kapunahala Stream
Sub-basin 4 consists of __ acres of mostly steeply sloped land on the east side of Pu`u Keahiakahoe, rising to 2820 ft (860 m). Most of the perennial flow in Kapunahala Stream comes from Kea`ahala Spring at around 280 ft elevation. Portions of this spring are diverted to kalo lo`i that are maintained by Kaneohe State Hospital and Windward Community College. The flow disappears into a wetland above Pookela Street (below Hope Chapel), then emerges at several points to be directed into a culvert under Pookela. At this point, the stream passes through developed (urban) lands of Kane`ohe town. Below Kuahulu Place, the stream enters a concrete-lined channel that is a continuous feature all the way to the confluence with Kamo`oali`i Stream.

Photo 4, Culvert at Pookela St (Eric Guiinther)

Photo 5
Leaving a wetland above Pookela Street, flow is directed into a culvert at the start of the urban land use portion of this sub-watershed.

Sub-basin 5: Kane`ohe Stream
Sub-basin 5 covers some __ acres of generally low elevation lands in urban Kaneohe town. This sub-basin includes all of Kane`ohe Stream (in the narrow sense) and the estuary of the Kane`ohe Stream system. Although the stream cuts a narrow swath of natural landscape through residential neighborhoods (and the Kaneohe Civic Center), the stream channel has been modified by grading and shaping. Concrete-rock masonry walls are present along the segment between the top of the sub-basin and the Kaneohe Civic Center, in the vicinity of which Kamehameha Highway crosses over the stream on a large bridge.

Water quality was monitored at TMDL Sta. 5 located at the end of Wena Place upstream of the start of the estuary.

[PREVIOUS PAGE: Kane`ohe Watershed] | [NEXT PAGE: Kane`ohe Stream]

1 Written by Eric Guinther (AECOS Inc.) partly from information provided by Robert Bourke (Oceanit Laboratories).
A Alluvium is a deposit of sediment and rocks resulting from flowing water; colluvium is a deposit of soil and rock accumulated at the base of a slope.