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The proposed definition of "Freshwater Resources" in the NPS for Freshwater Management is: "Freshwater Resources means the fresh water of New Zealand's rivers, lakes, wetlands and groundwater systems [but does not include fresh water of any ephemeral stream or artificial watercourse]."

Several questions arise from this definition:

1. Why are ephemeral rivers/streams singled out here? What about other temporary waterbodies (e.g., ponds and wetlands)?

2. Doesn't this require a precise definition of ephemeral river/streams? - perhaps the intended definition of ephemeral streams was - "a stream channel filled only after unpredictable rain and by run-off, with the flooded area drying out during the days following flooding and rarely supporting macroscopic aquatic organisms."

3. Are ephemeral streams different from intermittent, episodic, seasonal, or near-permanent streams (again what is the definition of ephemeral stream?)?

4. Ephemeral streams often transition into perennial stream segments. Therefore, ignoring ephemeral streams in the management of fresh waters may have deleterious consequences for downstream "freshwater resources".

How should we respond to this weakness in the definition of "Freshwater Resources?:

Regardless of their inclusion or exclusion in this NPS, temporary water bodies must be defined in order to either ignore or embrace their management needs.

Ephemeral streams and other temporary waters have a diversity of geomorphological features that may make their boundaries difficult to define. For example, there are streams that dry in an upstream direction, downstream direction, or have mid-reaches that run dry. Dry reaches can be seasonally dry, unpredictably dry, and/or infrequently dry. Most ephemeral streams are connected to perennial reaches along the same continuous flow path and this makes their boundaries even more difficult to determine without long-term data. However, most ephemeral streams have a well defined geomorphic structure that makes the evidence of overland flow obvious to the casual observer (i.e., the presence/absence of certain ephemeral stream channels can relatively easy to locate in the field [with some exceptions]).

How do we define ephemeral streams? - hydroperiod, geomorphology, riparian veg? Perhaps it's constructive to look at regulatory definitions elsewhere for definitions of temporary waterbodies. For example, in order to enforce parts of the US Federal Clean Water Act that protect wetlands in the US (including temporary wetlands), the US Army Corps of Engineers use hydrology, soils, and vegetation to delineate wetland boundaries. For hydrology, a wet area is considered a wetland if it is saturated within 1 foot of the soil surface for 5 - 12.5% of the growing season in most years (about every other year on average). This definitions has been disputed but is an established and enforceable rule for delineating wetland boundaries.

One definition (Williams 2006, Biology of Temporary Waters) states that all temporary waters are, for the most part, natural bodies of water which experience a recurrent dry phase (often predictable both in its time of onset and duration). The defining element is the cyclical nature of the drought, as some permanent waterbodies may dry up in exceptionally dry years. In New Zealand, the recurrence of drying may be frequent (e.g., 1-5x/year) or infrequent (once every 5 years) and may be aseasonal in some areas but seasonal in other areas.

It is likely that for ephemeral streams in New Zealand, a combination of hydrologic and geomorphologic indices may be useful in for definition and delineation. For example, a well defined channel (something greater than zero order), continuous flow for less than 99% and greater than 1% of the time for most years?

Comments, edits, additions welcome...