# Reference water levels > Mediated Wiki article. Canonical URL: https://mediated.wiki/source/Reference_water_levels > Markdown URL: https://mediated.wiki/source/Reference_water_levels.md > Source: https://en.wikipedia.org/wiki/Reference_water_levels > Source revision: 1255220368 > License: Creative Commons Attribution-ShareAlike 4.0 International (https://creativecommons.org/licenses/by-sa/4.0/) {{Short description|River navigation parameters}} The '''reference water levels''' are used on [inland waterway](/source/inland_waterway)s to define a range of [water level](/source/water_level)s allowing the full use of the waterway for [navigation](/source/navigation).{{sfn|Muilerman|Maierbrugger|Armbrecht|Schepper|2018|p=63}} Ship passage can be limited by the water levels that are too low, when the [fairway](/source/Fairway_(navigation)) might become too shallow for large ("target", "design") ships, or too high, when it might become impossible for the target ships to pass under the bridges.{{sfn|Muilerman|Maierbrugger|Armbrecht|Schepper|2018|p=63}} The goal of establishing the reference water levels is to balance the safety of navigation and economic value of the waterway{{cite journal | last1 = Wang | first1 = Lu | last2 = Xie | first2 = Ping | last3 = Xu | first3 = Chong-Yu | last4 = Sang | first4 = Yan-Fang | last5 = Chen | first5 = Jie | last6 = Yu | first6 = Tao | title = A framework for determining lowest navigable water levels with nonstationary characteristics | journal = Stochastic Environmental Research and Risk Assessment | date = 2 August 2021 | volume = 36 | issue = 2 | pages = 583–608 | issn = 1436-3240 | eissn = 1436-3259 | doi = 10.1007/s00477-021-02058-1 | pmid = | hdl = 10852/92995 | s2cid = 236780910 | url = https://www.duo.uio.no/bitstream/handle/10852/92995/1/20%2529%2BWang%2BLU%2BSERRA.pdf }} (for example, increase of the low level shortens the [navigation season](/source/navigation_season) but allows the use of larger ships). Reference levels are set up based on statistics obtained from the multi-decadal observations (typically 30 years).{{sfn|Muilerman|Maierbrugger|Armbrecht|Schepper|2018|p=64}} == Free-flowing rivers == Free-flowing rivers use the '''low navigable water level''' (also '''lowest navigable water level''', '''LNWL''') as a low reference water level.{{sfn|Muilerman|Maierbrugger|Armbrecht|Schepper|2018|p=64}} When the river is at or above LNWL, the ships of the target [draft](/source/Draft_(hull)) can use its fairway.{{sfn|Muilerman|Maierbrugger|Armbrecht|Schepper|2018|p=14}} LNWL is usually defined as the water level that the river surface stays mostly above at the times when the river is navigable (e. g., during the ice-free season in Europe),{{sfn|Muilerman|Maierbrugger|Armbrecht|Schepper|2018|p=64}} so that the river level on average stays below the LNWL only for a fixed small portion of a year. For example, in Europe the limit of time below LNWL is 20 ice-free days per year (e. g., on [Rhine](/source/Rhine)) or, alternatively, corresponds to 5–6% of the ice-free period on European rivers (6% on [Danube](/source/Danube){{sfn|Muilerman|Maierbrugger|Armbrecht|Schepper|2018|p=64}}).{{sfn|UNECE|2017|p=15}} The '''highest navigable water level''' ('''HNWL''') is defined as a water level that is exceeded for only a few days a year (usually 1%). == Regulated rivers, canals == The low reference level is usually not defined for [regulated rivers](/source/River_engineering) and [canal](/source/canal)s, as in these cases the depth of the navigation channel is guaranteed by design (sufficient margins are covering the variations of the flow).{{sfn|Muilerman|Maierbrugger|Armbrecht|Schepper|2018|p=63}} The high reference water level (MHW) is sometimes set to accommodate the short-term variations (for example, [tidal](/source/tide) effects, usually at the levels observed 1% of the time) and the effect of water level changes due to the operation of [locks](/source/Lock_(water_navigation)) and [weir](/source/weir)s.{{sfn|Muilerman|Maierbrugger|Armbrecht|Schepper|2018|p=63}} == Equivalent water level == In Germany, an '''equivalent water level''' ({{langx|de|Gleichwertiger Wasserstand}}, '''GlW''') is the value of a [stream gauge](/source/stream_gauge) that corresponds to the nominal [fairway depth](/source/fairway_depth) (ideal minimum channel depth, TuGlW).{{sfn|Muilerman|Maierbrugger|Armbrecht|Schepper|2018|p=67}} == See also == *[Chart datum](/source/Chart_datum) *[Vertical datum](/source/Vertical_datum) == References == {{Reflist}} == Sources == * {{cite book |last1=Muilerman | first1=Gert-Jan | last2=Maierbrugger | first2=Gudrun | last3=Armbrecht | first3=Henrik | last4=Schepper | first4=Karin de | last5=Turf | first5=Sim | last6=Liere | first6=Richard van | last7=Quispel | first7=Martin |title=Good Navigation Status: guidelines towards achieving a Good Navigation Status |date=2018 |publisher=[Publications Office of the European Union](/source/Publications_Office_of_the_European_Union) |location=Luxembourg |url=https://data.europa.eu/doi/10.2832/148049 | isbn=978-92-79-81043-5 | doi=10.2832/148049 }} * {{cite book |last1=UNECE |title=Inventory of Main Standards and Parameters of the E Waterway Network (Blue Book) |date=2017 |publisher=[United Nations Economic Commission for Europe](/source/United_Nations_Economic_Commission_for_Europe) |location=New York and Geneva |edition=3rd |url=https://unece.org/sites/default/files/2021-01/ECE-TRANS-SC3-144-Rev.3e_0.pdf}} Category:Nautical terminology Category:Navigation {{water-transport-stub}} --- Adapted from the Wikipedia article [Reference water levels](https://en.wikipedia.org/wiki/Reference_water_levels) by Wikipedia contributors ([contributor history](https://en.wikipedia.org/wiki/Reference_water_levels?action=history)). 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