Mystery of the 3 USGS Gages in Mānoa

The runoff ratio is how much runoff responses to the rainfall. Here, we use the NCDC HMNL rainfall data (the diamond symbol in Waihi subwatershed on the Annual Rainfall Map), and 3 USGS gages and their information of the drainage areas.

Why do we need drainage area? Because both of runoff and rainfall represents as depth over the watershed area. (Notice the tricky part here: we assume both of runoff and rainfall depths are well-distributed/homogeneous, but they are usually not…)

Waihi Runoff Ratio

Waihi runoff ratio shows an extreme runoff response to the rainfall, which may indicate:

  • Waihi watershed has a very permeable surface with a threshold for overland flow (Wikipedia: overland flow).
  • Either runoff or rainfall is not well-spatially (homogeneously) distributed

Besides, we can also notice that the runoff ratio excessed 100% sometimes, which means the runoff we got is more than the rainfall we observed. It whispers to us: either rainfall or runoff is not well-spatially distributed  OR there is some extra water pouring into the stream.


Waiakeakua Runoff Ratio

With a similar drainage area, Waiakeakua’s runoff response more to the rainfall than Waihi’s runoff! Moreover, there were more runoff ratios larger than 100%… It looks not like only because of inhomogeneous of runoff or rainfall, but more likely some additional water input to the Waiakeakua stream.


Mānoa-Woodlawn Runoff Ratio

Surprisingly, Mānoa-Woodlawn runoff ratio has a similar pattern with Waihi but not Waiakeakua. I’d like to guess that there were more groundwater discharge to the Waiakeakua streams, but not Waihi and Mānoa streams. I wonder, which stream has more groundwater discharge since USGS Waiakeakua gage is actually the confluence of three streams.




Hydrograph of 3 USGS Gages in Mānoa

A hydrograph is a time-series graph showing the rate of streamflow (discharge) a specific point in a river, a stream, or another channel. We can understand the streamflow rate changes with time at the point in the stream by a hydrograph.

The streamflow is related to rainfall, thus we like to put them together and see. However, we notice that the stream gage and rain gage usually are not at the same point. For example, in Mānoa watershed, we have three stream gages but only one rain gage (see the Mānoa Annual Rainfall Map in Map Page). It is such a pain for hydrologist…(now we should learn that nature is not a separated system, we better communicate with different field first, and then set up our observation stations…) Moreover, a stream gage is at a point of a stream, but it collects all the runoff (the water flow) from the entire watershed. Besides, point rainfall cannot represent the rainfall in entire watershed, neither. Thus we have to be very aware while we’re interpreting the rainfall and streamflow at each stream gage.

Waihī USGS Stream Gage

Waihī stream gage is the one closest to the rain gage, so the streamflow responses to the rainfall should be the most accurate within three stream gages. The minimum discharge (flow) at Waihi gage is about 0.002 cms on 2/11/2012, which is almost no flow…, and the maximum discharge is 6.8 cms on 12/13/2011 during the data period. The mean discharge of Waihi gage is about 0.09, which is more than three times ‘Aihualama stream. It’s very obvious that the streamflow didn’t response to the rainfall the same way (sometimes larger discharge with larger rainfall, but sometimes more rainfall has okay discharge)


Waiakeakua USGS Stream Gage

Waiakeakua stream gage has mean discharge 0.13 cms, including minimum discharge, 0.037, on 1/17/2014 to 1/20/2017 and maximum discharge, 1.71 cms on 9/15/2015. We noticed that the discharge from Waiakeakua is not as extreme as Waihī. There are some possibilities:

  1. There is more groundwater discharge into Waiakeakua stream (since the minimum discharge at Waiakeakua is much higher than the minimum discharge at Waihī)
  2. The rainfall amount is not the same at Waihī and Waiakeakua, especially heavy rainfall (because the maximum discharge at Waiakeakua is much lower than the maximum discharge at Waihī)
  3. The flow paths are different in each watershed. The flow paths influence the time the water stays on or in the ground until it goes into the stream.
    • The slopes of each watershed are different. I think that the discharge will increase immediately if the slope is steeply toward to the stream.
    • Geology and soil distributions lead the distribution of infiltration rate. The infiltration rate plays an important role in the flow paths.
    • The shapes of each watershed are different. The water paths may also related to the shape of a watershed.


Mānoa-Woodlawn USGS Stream Gage

Mānoa-Woodlawn stream gage has much higher discharge than Waihī and Waiakeakua because of its larger drainage area that allows the stream gain more water. The maximum discharge, 8.27 cms, occurred on 7/24/2016, and minimum discharge, 0.057, occurred on 12/8/2012.



(All the figures in this post are from Yu-Fen through R programming, the rainfall data is from NCDC, and discharge data is from USGS)

‘Aihualama Stream


‘Aihualama Stream is a very small stream (we even can’t see the stream from google map). In normal days, the stream width is less than 3 m (9.84 ft) with mean discharge 0.021/0.74 cubic meter per second/cubic feet per second (cms/cfs). With mean daily rainfall, 10.7 mm (0.42 inches), the mean discharge of the Mississippi rever is 16791.8 cms (593000 cfs). [Note: the rainfall data is from NOAA’s National Climatic Data Center (NCDC); the data of ‘Aihualama Stream is from Tsang Hydrology Lab]

Although ‘Aihualama is small, don’t ignore the power of our mother nature! The streamflow can increase rapidly during a rainfall event (the discharge can hit 20 times of normal discharge during hours!!! So be careful while you’re hiking on a rainy day in Hawaii!!!). The first figure below is showing the stream on a normal day, and water can reach the orange lines during a rainfall event. As Oki (2003) pointed out, Hawaiian streams are very flashy, ‘Aihualama is not excluded (see the second picture below)


Stream Ecosystem

So, who lives in this extreme flow amount stream? I guess the stream animals must have the ability to hide or hold tightly on the bottom that they won’t be flush away from a high, fast and turbulent flow. Besides, they have to tolerate the small amount of stream flow, which may cause the larger fluctuate in temperature, discontinuous stream and smaller habitat.

I saw a lot of small suckermouth armored catfishes in pools (not showing here), and crayfishes (the first photo below), guppies along the entire stream. They’re considered as invasive species for Hawai’i; they occupied the stream, and some of them eat the native species’ eggs (Devick 1989) . Also, there is an argument saying invasive fishes would impact the nutrient content and water quality in streams (Nico 2006; Capps et al. 2009)

Did I only see invasive fishes in ‘Aihualama stream? Well, I still see one or two o’opu (as the second photo), Hawaiian native goby, in the pool within like more than 30 catfishes…

On the stream bank, I saw a green and black poison dart frog (Dendrobates auratus) (the third photo below), this small tree frog is native to Central and South America. As their name implies, blow darts were rubbed on the back of frogs by indigenous tribes to make poison-tipped darts. They were introduced to Manoa Valley in the 1950s to control mosquitoes; however I didn’t find any evaluation for its consequence. More and more…. I ALWAYS GOT MOSQUITO BITTEN every time I went there…


Black small mushrooms (?) on a dead wood across the ‘Aihualama stream… I don’t know the name of the mushrooms, but it smelled not good…


Human Activities

On the right bank of ‘Aihualama stream at Lyon Arboretum, there are lo’i (taro farm; the first picture below), which is a part of Hawaiian cultural practicing. Some people and students go there every Wednesday to plant kalo (taro). For the farming, they need to divert the stream water into their farms, thus they use pipes (the second and third photo below) to divert the stream water into their lo’i. Most of the streams in Hawaiian are diverted for agriculture purpose; however, the water issues and conflicts increased during and after the sugar cane and pineapple plantations. How we manage the water resources and communicate with our friends living together are big challenges for us…



Capps, K.A. and Flecker, A.S., 2013, October. Invasive aquarium fish transform ecosystem nutrient dynamics. In Proc. R. Soc. B (Vol. 280, No. 1769, p. 20131520). The Royal Society.

Devick, W.S., 1989. Disturbances and fluctuations in the Wahiawa Reservoir ecosystem. Honolulu: Hawaii Department of Land and Natural Resources, Division of Aquatic Resources.

Nico, L., Fuller, P., Cannister, M. and Neilson, M., 2006. Pterygoplichthys disjunctivus. USGS Nonindigenous Aquatic Species Database, Gainesville, FL. Revision Date, 4(21), p.2006.

Oki, D.S., 2003. Surface water in Hawaii. US Department of the Interior, US Geological Survey.

(All the photo in this post were taken by Yu-Fen Huang/yfhuang)

The “shaka sloth” I met along the stream! 😀IMG_8972.JPG

USGS Gages in Mānoa

If we want to have a better understanding for a stream, or even have the abilities to manage a stream and water resources, we need a quantitative analysis. The data from stream gages will definitely help us to figure out how much flow/stream water we have.

U.S. Geophysical Survey (USGS) has 7 gages in Mānoa-Pālolo watershed (as the map below, including 4 in Mānoa, 2 in Pālolo, and one at the confluence of both). Since we’re going to focus on the Mānoa watershed first, three USGS gages have been selected:

  1. Waihi Stream gage: the confluence of ‘Aihualama, Lua’alaea and Waihi streams
  2. Waiakeakua Stream gage: the confluence of Wa’aloa, Naniuapo and Waiakeakua streams
  3. Manoa Stream at Woodlawn Drive gage: the confluence of Waihī and Waiakeakua streams
  4. (We don’t include the Manoa Stream at Kanewai Field gage because of it only have data for few days)


Gage Data Ability

The data ability of streamflow (discharge) data and water quality of 3 gages are listed below (current: 15-min interval discharge; daily: daily discharge; water quality data only provides few days in years):



Streamflow Summary

The stream summary from the USGS, and I converted the unit here. According to the drainage areas of each stream are very small comparing to the drainage areas in the Continental U.S. (CONUS). Besides, the maxima and minima of the streams also show the extreme streamflow condition, which may impact on the niches or habitat of the stream shrimps, fishes, and other. Baseflow indicates the permanent flow contributing to the total streamflow, and quick flow indicates the stormflow contributing to the total streamflow. The Waiakeakua stream has higher baseflow contribution than quick flow contribution may because it has groundwater discharge into the stream.




Mānoa Watershed – Where Mo’o live

Mānoa watershed starts with 6 streams and down to Waikiki (Ala Wai Canal after 1920):
(from Eva side toward Diamond Head side)
1. ‘Aihualama
2. Lua’alaea
3. Waihī
4. Wa’aloa
5. Naniu’apo
6. Waiakeakua

In the past, the entire Mānoa valley was full of lo’i (taro farm) because the valley is wide and flat, which is suitable for irrigation. (Sterling and Summers 1978)

Mo’o (water lizard) is one of aumakua (ancestral gods). Mo’o loves to live in rainy cliffs, mountain peaks, waterfalls, springs, streams, and pools of Mānoa (Sterling and Summers 1978). Mo’o likes wet environment; the upper Mānoa receives plenty rainfall as the previous folk story, Princess of Mānoa told us. Also, if we can check Hawaiian Rainfall Atlas, we will realize that the annual rainfall on the top of Mānoa is about 3900 mm (153.5 inches).

Mānoa was known for mo’o water spirits. They were usually shown in females with the form of large lizards. Mo’o controls water resources of  Mānoa valley, and usually brought the blessing of fish harvest, health to people, and welfare to the family and their friends. (Kamakau et al.1964).


Kōnāhuanui — Home of Mo’o


Sterling, E.P. and Summers, C.C., 1978. Sites of Oahu. Bishop Museum Pr.

Kamakau, S.M., Barrère, D.B. and Pukui, M.K., 1964. Ka Poʻe Kahiko: The People of Old. Bishop Museum Press.

Waihi Stream – Mānoa Fall

Instead of visiting Waiakeakua first, I visited Mānoa fall, Waihi Stream. According to my friend, Waiakeakua is more challenging, and my adventure friend got sick on the date that we were planning to visit Waiakeakua stream.

Mānoa fall belongs to Waihi Stream, and it’s an easy trail but very muddy…

Tropical and rainforest plants:R0015235.JPG

Mānoa fall! We heard that it’s better not to swim in the pool because of the bacteria… 😦R0015247.JPG


We found a way to climb up and tried to get to the top of Mānoa fall. :p1452110_567732963305683_381069119_n.jpg

The top of Mānoa fall! 😀R0015256.JPG

Only a few amount of water flowing actually…R0015257.JPG

Going down is the most terrifying part… R0015262.JPG

Natural History from the Folk Story – Princess of Mānoa

I want to start this blog with the Hawaiian folk story — princess of Mānoa, Kahalapuna. In the story, we can peek how the climate and biota in Mānoa were in the past.

The stream and plants in the story are colored and are listed below with photos! 🙂

The story is from:

Hawaiian folk tales: A collection of Native legends. AC McClurg, 1912.


This is how the story starts:

color indicators
Aqua — stream / Orange — biota / dark red — climate

“AKAAKA (laughter) is a projecting spur of the mountain range at the head of Manoa Valley, forming the ridge running back to and above Waiakeakua, “the water of the gods.” Akaaka was united in marriage to Nalehuaakaaka, still represented by some lehua (Metrosideros polymorpha) bushes on the very brow of the spur or ridge. They had two children, twins, Kahaukani, a boy, and Kauakuahine, a girl. These children were adopted at birth by a chief, Kolowahi, and chiefess, Pohakukala, who were brother and sister, and cousins of Akaaka. The brother took charge of the boy, Kahaukani, a synonym for the Manoa wind; and Pohakukala the girl, Kauakuahine, meaning the famous Manoa rain. When the children were grown up, the foster parents determined that they should be united; and the children, having been brought up separately and in ignorance of their relationship, made no objections. They were accordingly married and a girl was born to them, who was called Kahalaopuna. Thus Kolowahi and Pohakukala, by conspiring to unite the twin brother and sister, made permanent the union of rain and wind for which Manoa Valley is noted; and the fruit of such a union was the most beautiful woman of her time. So the Manoa girls, foster children of the Manoa rains and winds, have generally been supposed to have inherited the beauty of Kahalaopuna.

A house was built for Kahalaopuna at Kahaiamano on the road to Waiakekua, where she lived with a few attendants. The house was surrounded by a fence of auki  (dracaena), and a puloulou (sign of kapu) was placed on each side of the gate, indicative of forbidden ground. The puloulou were short, stout poles, each surmounted by a ball of white kapa cloth, and indicated that the person or persons inhabiting the premises so defined were of the highest rank, and sacred.

Kahalaopuna was very beautiful from her earliest childhood. Her cheeks were so red and her face so bright that a glow emanated therefrom which shone through the thatch of her house when she was in; a rosy light seemed to envelop the house, and bright rays seemed to play over it constantly. When she went to bathe in the spring below her house, the rays of light surrounded her like a halo. The natives maintain that this bright light is still occasionally seen at Kahaiamano, indicating that the spirit of Kahalaopuna is revisiting her old home.

She was betrothed in childhood to Kauhi, the young chief of Kailua, in Koolau, whose parents were so sensible of the honor of the contemplated union of their son with the Princess of Manoa, who was deemed of a semi-supernatural descent, that they

always sent the poi of Kailua and the fish of Kawainui for the girl’s table. She was thus, as it were, brought up entirely on the food of her prospective husband.

… (I’ll stop here, but I’ll list the biota showed up in the story)”

(If you’re interested in the story, please get the book, Hawaiian folk tales: A collection of Native legends. AC McClurg, 1912., mahalo!)

Waiakeakua, “the water of the gods.”

(photo taken by Easy Hiker Hawaii)



(photo by yfhuang at Aihualama stream in April 2017)


lehua (Metrosideros polymorpha)

(photos from here)


auki  (dracaena)

ti_leaf.jpg(photo by yfhuang at Lyon Arboretum in September 2016)

Dracaena & Cordyline (credit: Hawaiian Sunshine Nursery)

The Dragon Tree and the Ti plant… Dracaenas and Cordylines are similar plants and at one time Cordylines were classified as Dracaenas. The Cordyline or Ti plant is a Hawaiian native and is known as the “Hawaiian Good Luck Plant.” Aside from being a wonderful indoor plant, Ti leaves are traditionally used to wrap foods in Hawaiian recipes.



hala (Pandanus odoratissimus) tree

(photo by yfhuang at Lyon Arboretum in April 2017)


Wiliwili (Erythrina monosperma)

(photo from Onei)


Koa (Acacia koa) tree

Young koa.jpg (photo from Wikipedia)


Elepaio (Chasiempis sandwichensis)

(photo from Hayataro Sakitsu)
(Note: Elepaio is endemic to Hawaiian Island; however, it is recently endangered… ): )

Pueo (Asio flammeus sandwichensis)

Starr 090112-0857 Asio flammeus sandwichensis.jpg
(Photo from Wikipedia at Kanaha beach, Maui)
(Note, Pueo, a short-eared owl, is endemic to Hawaii.  It’s one of physical forms of ʻaumākua (ancestor spirits) in Hawaiian culture.  Since it might be a symbol, it’s hard to say if the pueo really showed up in Mānoa or it is just added in this fold story. But yes, Pueo is endangered in Hawaii, and I couldn’t find a pueo photo taken on Oahu…)

A-pe (Calladium costatum)

(photo from BigHawaii)


Kalo (Colocasia antiquorum)

(photo by yfhuang at Hawaiian Study Center in University of Hawaii at Manoa in March 2017)


Ha-u (hibiscus)

(photo by yfhuang in the University of Hawaii at Manoa in March 2017)