Author: SCOTT

Scott Werden @ Wiki Wai

Mahi Pono, through their subsidiary EMI, gets the bulk of their irrigation water from East Maui streams. The permit they get from the Land Board states how much water they can take. But the courts have also imposed a cap on the diversion of stream water regardless of what the Land Board awards. These rules all affect the total amount of water but there is one additional rule that affects each individual stream, and that is the Instream Flow Standard (IFS). This blog post will explain what IFS is and the problems that exist with its implementation in East Maui.

This blog post topic is divided into three parts:

• Part I (this post) covers two rulings made by the Water Commission on IFS for East Maui Streams,
• Part II goes into the details of how an IFS is determined,
• Part III examines the difference between base flow and storm flow

2018 Ruling on Nahiku, Ke’anae and Honomanu Streams

The left side image is taken from the top of the diversion on the Makapipi Stream, looking up the stream. The right side image is from the same location but looking downstream from the diversion. The stream is obviously dry below the diversion.

---

The first round of amending IIFS for East Maui Streams became official with the release of 2018 Decision & Order from the Water Commission (CWRM). In that decision, the Water Commission chose to first classify each stream by its potential beneficial uses. Those are summarized here:

• Connectivity. The instream use is primarily driven by habitat connectivity, that is, to allow migration of wildlife up and down the stream. This use can be satisfied with the lowest amount of instream water flow below a diversion.
• Habitat or H₉₀. This use also primarily benefits habitat and wildlife but provides for greater downstream water flow. In this case “H₉₀” means the goal is 90% survival rate for habitat.
• Traditional and Customary Use. The use here is appurtenant, that is, people who live on land that has stream water that was, and is, used for agriculture like kalo. This use can only be fulfilled by opening up the stream so there is no diversion and all water stays in the stream bed.

There is one category missing here: Off-stream use. The Water Commission’s approach to setting IFS is to enumerate the instream uses as required by law and then to basically allow all water that remains to be eligible for off-stream uses. What are those off-stream uses? Currently, for East Maui water, those are primarily agriculture, DHHL (Department of Hawai’i Homelands), and MDWS (Maui Department of Water Supply).

This approach by the Water Commission is not ideal for several reasons:

1. All instream uses must be accounted for and if a use is not considered, that use is going to suffer. For instance, streams are not completely independent of groundwater and de-watering a stream will also affect the aquifer. Is that properly accounted for in the current management method?
2. The East Maui water cycle is complex both on short- and long-time scales. Streams can be low flowing for weeks and then a big storm will turn them into a flood. Diverting water changes that flow pattern, and this is particularly bad in the method of diversion often used, which is to divert the base flow and leave the sporadic, storm floods in the streams.
3. While off-stream irrigation is a beneficial use, it is not necessarily of higher priority than an in-stream use, yet the Water Commission awards the most sought-after component of stream flow, base flow, to off-stream users.

2022 Ruling on Huelo Streams

Diversion on the Ho’olawali’ili’i Stream at the Lowrie Ditch. The stream is coming in from the top-center. The ditch is the channel on the right.

---

In 2021 the Sierra Club filed a petition to amend the IIFS for 12 additional streams, all located in the Huelo lease area. In 2022 the Water Commission staff released a recommendation  for amended IFS for 17 streams (they included branches and alternate names of the original 12).

The recommendation is very different from the 2018 D&O.

• The Water Commission added new management goals, in particular, Recreational Use and Riparian Use. The latter is for people who live on the stream and rely upon it for domestic and/or agricultural activities. The 2018 ruling considered traditional and cultural use which largely meant kalo agriculture, but in 2022 that is replaced with the broader category of Riparian Use.
• The Water Commission in 2022 has replaced an in-stream flow value with an order of what certain diversions must pass onward in the stream. Sometimes this is a percent, sometimes a range of flow. It is not always clear how these newer specs will relate to conditions in the stream so we anticipate some “tuning” of these specs in the future.
• Some of the 2022 recommendations include specific changes to the EMI diversions themselves. But it is not clear how they determined some of the changes ordered as they provide no calculations or engineering diagrams.

Summary

The complete text of the 2018 ruling covering streams in Nahiku, Ke’anae, and Honomanu, see CCHMA1301-20180620-CWRM-Fact-Law-Final.

For the CWRM staff recommendation for Huelo stream IFS, see sb20221115B5-CWRM Submittal B5 to restore Huelo streams.

The following table is a summary of CWRM orders for all affected streams in East Maui. Further details can be found on the Stream Portal of the wikiwai.org website.

Stream	Lease Area	CWRM Management Goal	CWRM IFS Order (cfs)	Median Flow @1200′ (cfs)
Makapipi	Nahiku	Full
Hanawi	Nahiku	Connectivity	0.92	6.2
Kapaula	Nahiku	Connectivity	0.56	4.3
Wai’a’aka	Ke’anae	None	0.77	0.86
Pa’akea	Ke’anae	Connectivity	0.18	1.5
Waiohue	Ke’anae	Full		5.2
Pua’aka’a	Ke’anae	Connectivity	0.2	0.97
Kopiliula	Ke’anae	H90	3.2	6.6
E. Wailuaiki	Ke’anae	H90	3.7	7.7
W. Wailuaiki	Ke’anae	Full		8.9
Wailuanui	Ke’anae	Full		3.8
Ohi’a, Waianu	Ke’anae	None
Waiokamilo	Ke’anae	Full		6.1
Palauhulu	Ke’anae	Full		5.4
Pi’ina’au	Ke’anae	Full		0.38
Nua’ailua	Honomanu	Connectivity	2.2	0.46
Honomanu	Honomanu	H90	4.2	3.8
Punalau, Kolea	Honomanu	H90	4.9	6
Ha’ipua’ena	Honomanu	Connectivity	1.36	4.8
Puohokamoa	Huelo	Connectivity	1.1	8.7
Wahinape’e	Huelo	None	0.9
Waikamoi	Huelo	H90	3.8	6.6
Hanehoi	Huelo	Full		2
Huelo, Puolua	Huelo	Full
Kolea East	Huelo	Specific species habitat	0.08	0.3
Kolea West	Huelo			0.65
Punalu’u	Huelo
Ka’aeia	Huelo	Aquatic habitat	Flows < 1,8	1.3
O’opuola	Huelo	Aquatic habitat	Flows < 1,8	1
Puehu	Huelo
Na’ili’ilihaele	Huelo	Recreational uses	Flows < 5.5	13
Kailua	Huelo	Recreational uses and aquatic habitat	20% of flow	7.8
Hanawana	Huelo	Riparian uses	Some unknown percentage of the flow	0.5
Hoalua	Huelo			1.3
Waipi’o	Huelo	Riparian uses	Full flow below New Hamakua ditch	0.73
Ho’olawa nui	Huelo	Recreational uses	Flows < 1.2 @ Lowrie, 20% flow below New Hamakua	3
Ho’olawali’ili’i	Huelo	Recreational uses	Flows < 0.7 @ Lowrie, 20% flow below New Hamakua	3.3
Honopou	Huelo	Full		2

Scott Werden @ Wiki Wai

This post is a continuation of our series on East Maui Stream IFS (Instream Flow Standard). The first part covered the legal rulings on two groups of East Maui streams, this part will go into the details of how each stream’s IFS is derived. The last part examines the difference between diverting base flow and storm flow.

Instream Flow Standard

Accord to State law (HRS § 174C-3), “‘Instream flow standard’ means a quantity or flow of water or depth of water which is required to be present at a specific location in a stream system at certain specified times of the year to protect fishery, wildlife, recreational, aesthetic, scenic, and other beneficial instream uses.”.

Stream Flow Metrics

The Water Commission uses statistical measures, like “90% of the time the water flow must be at least X”. They have a shorthand for that, that looks like this: B₉₀ or T₉₀. The letter indicates the type of flow, the number indicates the percentage of days the flow is at or above. So, for instance, B₉₀ = 5.0 cfs means 90% of the time (or 330 days out of the year) the base flow must be at least 5.0 cfs.  A high percentage value, such as B₉₀, is the most commonly found flows so this number is going to be used for beneficial uses that require reliable flow.

What is Base Flow?

The Water Commission divides raw stream flow into two regimes:

• Base Flow. This is flow that is due to springs, cloud drip, and leakage of soil. It excludes runoff from rainfall. It should be present most of the time.
• Total Flow. This is base flow + the runoff from rainfall (we call the latter, “excess flow” here). It is sporadic but accounts for a significant amount of water in East Maui.

Why do this? Base flow values are the most dependable values for stream flow since it does not depend on rainfall runoff. Everybody wants to have access to base flow because it is most reliable. The Water Commission recognizes that and uses base flow quality for setting IFS values. But here is the fly in the ointment – base flow statistics are used to specify instream flow yet the base flow is preferentially diverted for off-stream uses.

So how does all this relate to the real world of East Maui Streams? The following table should help illustrate that. This table is derived from the 2018 Decision & Order from the Water Commission for several (but not all) East Maui Streams.

Category of Instream Use	Formula for IFS	Example Streams
Connectivity	20% of BFQ90	Hanawi, Nua’ailua
Habitat or H90	64% of BFQ90	Kopiliula, Waikamoi
Traditional Use	100% of all Total Flow	Honopou, Waiokamilo

Notice that Connectivity and H₉₀ are both calculated from the 90% percentile of base flow. That is the flow that is present in an undiverted stream for at least 330 days out of the year. A percentage of that must be present in the diverted stream, and that is the IFS.

Confirming that IFS is Being Met

The law, specifically HRS § 174C-3, requires the IFS to include the time frame over which the flow value must be met or exceeded. This is not exactly adhered to in the 2018 D&O issued by the Water Commission, which states the following in regards to confirmation:

This is significant – the Water Commission is admitting it is not complying with the law when it only requires a one-year average rather than a minimum flow over a certain number of days, and it admits it is prioritizing an off-stream use of water (irrigation and domestic use) over instream use, even though off-stream use has a questionable legal status.

Diverting Streams

The story of IFS is not complete without talking about how streams are diverted. There are several different designs but many of the streams use a combination of a dam with a spillway, and a sluice gate. Appendix D of the 2021 EIS (Volume 2), calls this diversion type A, and it is the most common diversion design in East Maui. The dam-with-spillway is designed to separate base flow from the high-volume rainfall runoff, as described in the following excerpt from Volume 1 of the EMI 2021 EIS:

Ho’olawanui diversion. Input grate to the ditch. The stream bed is behind the man and with low to moderate flow it all goes in the grate and is diverted. High flow makes it past the grate and stays in the stream bed.

---

A sluice gate allows a portion of the diverted base flow to re-enter the stream bed but the gates are mechanical and have to be set by hand. In principle, each sluice gate can be set such that the instream flow complies with the IFS for that stream. But very few streams have active monitoring of downstream flow so the public has no visibility into whether the diversion is complying with the stream’s IFS, and since the Water Commission allows one-year average to be used, there is no real incentive to tuning the sluice gate to maintain some semblance of steady flow in the stream.

The IFS system for East Maui designed by the Water Commission is to a great extent differential to the needs of EMI – base flow is reliable and steady, which is good for commercial agriculture so by default, EMI gets the base flow. This prioritization has questionable legal basis to it, but that aside, there is a question of which portion of the flow (base flow or excess flow) will deliver the most water? We will defer answering that question to the next part in this series, which you can access here.

Further Reading and Resources

Document Name (and link to it)	Description
sb20260519C1	Progress report on modifying diversions in order to comply with the 2022 PAIFS ruling.
CWRM – Summary of Diversions in Huelo sb20220719B2	Summary of stream diversions in Huelo
Stream Portal	Wikiwai Map and list of IFS and other data for all streams that have been diverted by EMI.