{"id":13215,"date":"2021-10-08T09:05:08","date_gmt":"2021-10-08T08:05:08","guid":{"rendered":"https:\/\/www.vtei.cz\/?p=13215"},"modified":"2024-07-17T12:02:26","modified_gmt":"2024-07-17T11:02:26","slug":"mini-jet-device-as-a-tool-for-determination-of-soil-erodibility-characteristics","status":"publish","type":"post","link":"https:\/\/www.vtei.cz\/en\/2021\/10\/mini-jet-device-as-a-tool-for-determination-of-soil-erodibility-characteristics\/","title":{"rendered":"Mini-JET device as a tool for determination of soil erodibility characteristics"},"content":{"rendered":"

<\/i> This article is available in Czech only. For translation or more information on this topic, please contact author.<\/h4>\n

 <\/p>\n

SOUHRN<\/h2>\n

\u010cl\u00e1nek popisuje metodu stanoven\u00ed erodovatelnosti nesoudr\u017en\u00fdch zem\u011bd\u011blsk\u00fdch p\u016fd pomoc\u00ed m\u011b\u0159en\u00ed kritick\u00e9ho te\u010dn\u00e9ho nap\u011bt\u00ed. Pro ur\u010den\u00ed kritick\u00e9ho te\u010dn\u00e9ho nap\u011bt\u00ed byl pou\u017eit tzv. \u201eJet Erosion Test\u201c (JET). M\u011b\u0159en\u00ed bylo provedeno pomoc\u00ed modifikovan\u00e9 zmen\u0161en\u00e9 verze za\u0159\u00edzen\u00ed Mini-JET. Za\u0159\u00edzen\u00ed je velmi vhodn\u00e9 pro ter\u00e9nn\u00ed m\u011b\u0159en\u00ed, nebo\u0165 je mal\u00e9, lehk\u00e9, spot\u0159ebuje relativn\u011b n\u00edzk\u00e9 mno\u017estv\u00ed vody a\u00a0na jeho obsluhu posta\u010d\u00ed jedna osoba. Princip m\u011b\u0159en\u00ed kritick\u00e9ho te\u010dn\u00e9ho nap\u011bt\u00ed p\u016fdy je zalo\u017een na sledov\u00e1n\u00ed rychlosti tvorby erozn\u00edho kr\u00e1teru, kter\u00fd je vym\u00edl\u00e1n p\u016fsoben\u00edm vodn\u00edho paprsku o\u00a0zn\u00e1m\u00e9 kinetick\u00e9 energii. Z\u00a0pr\u016fb\u011bhu geneze erozn\u00edho kr\u00e1teru lze vypo\u010d\u00edtat erozn\u00ed parametry p\u016fdy, jako jsou kritick\u00e9 te\u010dn\u00e9 nap\u011bt\u00ed a\u00a0koeficient erodovatelnosti.<\/p>\n

V\u0161echny Mini-JET experimenty byly provedeny na experiment\u00e1ln\u00edch ploch\u00e1ch u\u00a0obce \u0158isuty a\u00a0byly pro n\u011b vyu\u017eity dva odli\u0161n\u00e9 typy p\u016fdn\u00edho povrchu. U\u00a0p\u016fdn\u00edho povrchu byly zji\u0161\u0165ov\u00e1ny p\u016fdn\u00ed charakteristiky (objemov\u00e1 hmotnost, zrnitostn\u00ed slo\u017een\u00ed, objemov\u00e1 vlhkost, stabilita p\u016fdn\u00edch agreg\u00e1t\u016f a\u00a0obsah organick\u00e9ho uhl\u00edku). Celkem bylo provedeno 75 simulac\u00ed.<\/p>\n

U\u00a0vypo\u010dten\u00fdch erozn\u00edch veli\u010din byla zji\u0161t\u011bna velk\u00e1 variabilita, kter\u00e1 je charakteristick\u00e1 pro nesoudr\u017en\u00e9 typy p\u016fdn\u00edch povrch\u016f. P\u0159esto jsou stanoven\u00e9 hodnoty koeficientu erodovatelnosti srovnateln\u00e9 s\u00a0publikovan\u00fdmi hodnotami, a\u00a0mohou tak b\u00fdt vyu\u017eiteln\u00e9 pro implementaci v\u00a0erozn\u00edch modelech. Na z\u00e1klad\u011b proveden\u00fdch test\u016f lze proto konstatovat, \u017ee metoda je vyu\u017eiteln\u00e1 i\u00a0na zem\u011bd\u011blsk\u00fdch p\u016fd\u00e1ch. Pro z\u00edsk\u00e1n\u00ed reprezentativn\u00edch hodnot erodovatelnosti je vzhledem k\u00a0vysok\u00e9 prostorov\u00e9 heterogenit\u011b prost\u0159ed\u00ed t\u0159eba prov\u00e9st dostate\u010dn\u00fd po\u010det replikac\u00ed.<\/p>\n

\u00daVOD<\/h2>\n

Eroze p\u016fd je p\u0159irozen\u00fd proces, kter\u00fd v\u00a0dlouhodob\u00e9m \u010dasov\u00e9m m\u011b\u0159\u00edtku p\u0159etv\u00e1\u0159\u00ed reli\u00e9f krajiny. Eroze je p\u016fsobena kombinac\u00ed r\u016fzn\u00fdch faktor\u016f. Kl\u00ed\u010dov\u00e9 jsou vlastnosti p\u016fdy a\u00a0jej\u00ed schopnost odol\u00e1vat p\u016fsoben\u00ed erozn\u00edch \u010dinitel\u016f (dopadu de\u0161\u0165ov\u00fdch kapek a\u00a0povrchov\u00e9mu odtoku vody). Problematick\u00e1 je eroze zrychlen\u00e1, p\u0159i n\u00ed\u017e se odplavuj\u00ed p\u016fdn\u00ed \u010d\u00e1stice a\u00a0agreg\u00e1ty tak rychle, \u017ee nemohou b\u00fdt nahrazov\u00e1ny pomalej\u0161\u00edm p\u016fdotvorn\u00fdm procesem. Zrychlen\u00e1 eroze je \u010dasto zp\u016fsobena z\u00e1sahy \u010dlov\u011bka v\u00a0krajin\u011b [1]. P\u0159\u00ed\u010dinami zrychlen\u00e9 eroze v\u00a0\u010cesk\u00e9 republice jsou krom\u011b jin\u00e9ho kolektivizovan\u00e1 zem\u011bd\u011blsk\u00e1 krajina, p\u0159etrv\u00e1vaj\u00edc\u00ed intenzifikace zem\u011bd\u011blstv\u00ed a\u00a0p\u011bstov\u00e1n\u00ed nevhodn\u00fdch plodin na nevhodn\u00fdch pozemc\u00edch\u00a0[2]. T\u00edm doch\u00e1z\u00ed k\u00a0postupn\u00e9mu zmen\u0161ov\u00e1n\u00ed mocnosti p\u016fdn\u00edho profilu, a\u00a0tedy ke sn\u00ed\u017een\u00ed \u00farodnosti p\u016fdy a\u00a0n\u00e1sledn\u00fdm ztr\u00e1t\u00e1m v\u00a0zem\u011bd\u011blstv\u00ed. Vlivem transportu p\u016fdn\u00edch \u010d\u00e1stic se pak sediment usazuje v\u00a0pat\u00e1ch svahu, ve vodn\u00edch toc\u00edch a\u00a0n\u00e1dr\u017e\u00edch.<\/p>\n

Erodovatelnost p\u016fdy je charakteristika, kter\u00e1 popisuje n\u00e1chylnost konkr\u00e9tn\u00edho p\u016fdn\u00edho povrchu k\u00a0erozi [3]. Vy\u0161\u0161\u00ed m\u00edra erodovatelnosti vede k\u00a0vy\u0161\u0161\u00edmu smyvu pro konkr\u00e9tn\u00ed erozn\u011b \u00fa\u010dinnou sr\u00e1\u017eku p\u0159i zachov\u00e1n\u00ed ostatn\u00edch po\u010d\u00e1te\u010dn\u00edch a\u00a0okrajov\u00fdch podm\u00ednek. Z\u00a0toho d\u016fvodu vstupuje erodovatelnost povrchu p\u016fdy jako parametr do \u0159ady fyzik\u00e1ln\u011b zalo\u017een\u00fdch erozn\u00edch model\u016f [3\u20136]. V\u00a0z\u00e1vislosti na koncepci modelu je erodovatelnost vyj\u00e1d\u0159ena r\u016fzn\u00fdmi zp\u016fsoby a\u00a0je odvozena z\u00a0r\u016fzn\u00fdch charakteristik p\u016fdy (fyzik\u00e1ln\u00edch i\u00a0chemick\u00fdch). Za hlavn\u00ed ur\u010duj\u00edc\u00ed parametry erodovatelnosti jsou obvykle pova\u017eov\u00e1ny: zrnitostn\u00ed slo\u017een\u00ed, obsah organick\u00e9ho uhl\u00edku, skeletovitost, stabilita p\u016fdn\u00edch agreg\u00e1t\u016f a\u00a0hydraulick\u00e1 vodivost [7].<\/p>\n

V\u00a0modelech matematicky popisuj\u00edc\u00edch erozn\u00ed proces [6] je inici\u00e1ln\u00ed erodovatelnost mezir\u00fdhov\u00e9, respektive plo\u0161n\u00e9 eroze z\u00e1visl\u00e1 na kritick\u00e9m te\u010dn\u00e9m nap\u011bt\u00ed dan\u00e9ho povrchu p\u016fdy [8], na n\u011bm\u017e se krom\u011b v\u00fd\u0161e uveden\u00fdch vlastnost\u00ed p\u016fdy pod\u00edl\u00ed i\u00a0stav povrchu, tedy nakyp\u0159enost, krusta vytvo\u0159en\u00e1 p\u0159edchoz\u00edmi sr\u00e1\u017ekami a\u00a0konsolidac\u00ed p\u0159i vysych\u00e1n\u00ed, drsnost povrchu aj. Kritick\u00e9 te\u010dn\u00e9 nap\u011bt\u00ed je hodnota smykov\u00e9ho nap\u011bt\u00ed vyvolan\u00e1 kinetickou energi\u00ed vodn\u00edho proudu (sr\u00e1\u017eka, povrchov\u00fd odtok), od kter\u00e9ho za\u010dne b\u00fdt povrch p\u016fdy rozru\u0161ov\u00e1n, jeho struktura se rozpad\u00e1 a\u00a0p\u016fdn\u00ed \u010d\u00e1stice (nebo rozplaven\u00e9 agreg\u00e1ty) za\u010d\u00ednaj\u00ed b\u00fdt un\u00e1\u0161eny vodn\u00edm proudem. Kritick\u00e9 nap\u011bt\u00ed lze stanovit na z\u00e1klad\u011b experiment\u016f s\u00a0de\u0161\u0165ov\u00fdm simul\u00e1torem nebo pomoc\u00ed um\u011bl\u00e9ho v\u00fdronu vody na sklonit\u00e9m p\u016fdn\u00edm povrchu. Tyto experimenty jsou \u010dasov\u011b a\u00a0finan\u010dn\u011b n\u00e1ro\u010dn\u00e9. V\u00a0praxi se proto v\u00a0matematick\u00fdch modelech \u010dasto vyu\u017e\u00edv\u00e1 nep\u0159\u00edm\u00fdch odvozen\u00ed na z\u00e1klad\u011b snadno m\u011b\u0159iteln\u00fdch charakteristik p\u016fdy. Nalezen\u00ed spolehliv\u00e9 metody pro p\u0159\u00edm\u00e9 m\u011b\u0159en\u00ed hodnot erodovatelnosti p\u016fdy, kterou by bylo mo\u017eno prov\u00e1d\u011bt rychle, snadno a\u00a0ve v\u011bt\u0161\u00edm po\u010dtu opakov\u00e1n\u00ed, by bylo velk\u00fdm p\u0159\u00ednosem pro spolehliv\u011bj\u0161\u00ed stanoven\u00ed erozn\u00ed ohro\u017eenosti zem\u011bd\u011blsk\u00fdch p\u016fd a\u00a0n\u00e1sledn\u00e9 navrhov\u00e1n\u00ed protierozn\u00edch opat\u0159en\u00ed.<\/p>\n

C\u00edlem\u00a0t\u00e9to pr\u00e1ce je p\u0159edstaven\u00ed metody stanoven\u00ed erodovatelnosti nesoudr\u017en\u00fdch zem\u011bd\u011blsk\u00fdch p\u016fd pomoc\u00ed m\u011b\u0159en\u00ed kritick\u00e9ho te\u010dn\u00e9ho nap\u011bt\u00ed. Pro ur\u010den\u00ed kritick\u00e9ho nap\u011bt\u00ed je testov\u00e1n tzv. \u201eJet Erosion Test\u201c, prov\u00e1d\u011bn\u00fd s\u00a0vyu\u017eit\u00edm modifikovan\u00e9ho za\u0159\u00edzen\u00ed Mini-JET. Toto za\u0159\u00edzen\u00ed bylo doposud pou\u017e\u00edv\u00e1no pro stanovov\u00e1n\u00ed kritick\u00e9ho te\u010dn\u00e9ho nap\u011bt\u00ed soudr\u017en\u00fdch p\u016fd (zejm\u00e9na pro posouzen\u00ed stability b\u0159eh\u016f a\u00a0dna vodn\u00edch tok\u016f). Metoda je ve sv\u011bt\u011b relativn\u011b roz\u0161\u00ed\u0159en\u00e1 [9\u201311]. Jej\u00ed vyu\u017eit\u00ed pro povrch zem\u011bd\u011blsk\u00e9 p\u016fdy je v\u0161ak zcela inovativn\u00ed a\u00a0jedn\u00e1 se o\u00a0prvn\u00ed takov\u00e9 vyu\u017eit\u00ed popisovan\u00e9ho za\u0159\u00edzen\u00ed [12].<\/p>\n

METODIKA<\/h2>\n

Princip m\u011b\u0159en\u00ed kritick\u00e9ho te\u010dn\u00e9ho nap\u011bt\u00ed p\u016fdy je zalo\u017een na sledov\u00e1n\u00ed rychlosti tvorby erozn\u00edho kr\u00e1teru p\u016fsoben\u00edm vodn\u00edho paprsku o zn\u00e1m\u00e9 kinetick\u00e9 energii. Z pr\u016fb\u011bhu geneze erozn\u00edho kr\u00e1teru lze vypo\u010d\u00edtat erozn\u00ed parametry p\u016fdy, jako jsou kritick\u00e9 te\u010dn\u00e9 nap\u011bt\u00ed a koeficient erodovatelnosti. Experimenty jsou prov\u00e1d\u011bny s\u00a0vyu\u017eit\u00edm za\u0159\u00edzen\u00ed Mini-JET, kter\u00e9 je pops\u00e1no d\u00e1le. Za\u0159\u00edzen\u00ed je velmi vhodn\u00e9 pro ter\u00e9nn\u00ed m\u011b\u0159en\u00ed, nebo\u0165 je mal\u00e9, lehk\u00e9, spot\u0159ebuje relativn\u011b n\u00edzk\u00e9 mno\u017estv\u00ed vody a\u00a0na jeho obsluhu posta\u010d\u00ed jedna osoba.<\/p>\n

P\u0159i hodnocen\u00ed erodovatelnosti p\u016fdy lze p\u0159edpokl\u00e1dat, \u017ee rychlost eroze \u03b5r<\/sub>\u00a0[m.s-1<\/sup>] je \u00fam\u011brn\u00e1 efektivn\u00edmu te\u010dn\u00e9mu nap\u011bt\u00ed. Eroze nast\u00e1v\u00e1 v\u00a0momentu, kdy efektivn\u00ed te\u010dn\u00e9 nap\u011bt\u00ed za\u010dne p\u0159evy\u0161ovat kritick\u00e9 smykov\u00e9 nap\u011bt\u00ed [11]:\"\"<\/a><\/p>\n\n\n\n\n\n
kde<\/td>\nkd<\/sub><\/td>\nje<\/td>\nkoeficient erodovatelnosti [m3<\/sup>.N-1<\/sup>.s-1<\/sup>]<\/td>\n<\/tr>\n
<\/td>\n\u03c4e<\/sub><\/td>\n<\/td>\nefektivn\u00ed te\u010dn\u00e9 nap\u011bt\u00ed [Pa]<\/td>\n<\/tr>\n
<\/td>\n\u03c4c<\/sub><\/td>\n<\/td>\nkritick\u00e9 smykov\u00e9 nap\u011bt\u00ed [Pa]<\/td>\n<\/tr>\n<\/tbody>\n<\/table>\n

Jet Erosion Test<\/h2>\n

JET (Jet Erosion Test) je technika pou\u017e\u00edvan\u00e1 p\u0159i studiu eroze a\u00a0mechanick\u00fdch vlastnost\u00ed p\u016fdy. Experiment\u00e1ln\u00ed vybaven\u00ed a\u00a0metodika pro JET test byly vyvinuty Hansonem a\u00a0kol. [13] ve Spojen\u00fdch st\u00e1tech americk\u00fdch. Princip spo\u010d\u00edv\u00e1 v\u00a0monitorov\u00e1n\u00ed eroze p\u016fdy vyvolan\u00e9 kolmo aplikovan\u00fdm proudem vody.<\/p>\n

Proud vody generovan\u00fd konstantn\u00edm tlakem proch\u00e1z\u00ed tryskou a\u00a0nar\u00e1\u017e\u00ed na povrch p\u016fdy. P\u016fdn\u00ed povrch je b\u011bhem experimentu zaplaven, tryska je zcela pono\u0159en\u00e1 ve vod\u011b, tud\u00ed\u017e n\u00e1sledn\u00e9 v\u00fdpo\u010dty erozn\u00edch parametr\u016f prob\u00edhaj\u00ed na z\u00e1klad\u011b dynamiky pono\u0159en\u00e9ho paprsku, jak ve sv\u00e9 publikaci popsali Hanson a\u00a0Cook [14]. Vodn\u00ed paprsek vych\u00e1zej\u00edc\u00ed z\u00a0trysky p\u016fsob\u00ed na povrch p\u016fdy smykovou silou, \u010d\u00edm\u017e se za\u010dne vytv\u00e1\u0159et erozn\u00ed kr\u00e1ter.<\/p>\n

Rozlo\u017een\u00ed te\u010dn\u00e9ho nap\u011bt\u00ed pod vodn\u00edm paprskem nen\u00ed rovnom\u011brn\u00e9, teoreticky je ve st\u0159edu n\u00e1razov\u00e9 z\u00f3ny nulov\u00e9 a\u00a0zvy\u0161uje se se vzr\u016fstaj\u00edc\u00ed radi\u00e1ln\u00ed vzd\u00e1lenost\u00ed od st\u0159edu a\u017e na okraj tryskov\u00e9ho proudu. Pot\u00e9 se toto nap\u011bt\u00ed se vzr\u016fstaj\u00edc\u00ed vzd\u00e1lenost\u00ed sni\u017euje. JET anal\u00fdza je zalo\u017eena na p\u0159edpokladu, \u017ee maxim\u00e1ln\u00ed smykov\u00e1 s\u00edla vodn\u00edho paprsku zp\u016fsob\u00ed maxim\u00e1ln\u00ed prohlouben\u00ed erozn\u00edho kr\u00e1teru [11].<\/p>\n

Ode\u010det hloubky erozn\u00edho kr\u00e1teru se prov\u00e1d\u00ed v\u00a0pr\u016fb\u011bhu erozn\u00edho experimentu. Po\u010d\u00e1te\u010dn\u00ed doba m\u011b\u0159en\u00ed by m\u011bla b\u00fdt co nejmen\u0161\u00ed, aby bylo mo\u017en\u00e9 dos\u00e1hnout co nejp\u0159esn\u011bj\u0161\u00edho pr\u016fb\u011bhu hloubky erozn\u00edho kr\u00e1teru, jeliko\u017e nejv\u011bt\u0161\u00ed smykov\u00e1 s\u00edla p\u016fsob\u00ed na za\u010d\u00e1tku testu a\u00a0s\u00a0rostouc\u00ed hloubkou kr\u00e1teru kles\u00e1. Test je pova\u017eov\u00e1n za dokon\u010den\u00fd, jakmile dos\u00e1hne hloubka erozn\u00edho kr\u00e1teru maxima (nedoch\u00e1z\u00ed k\u00a0dal\u0161\u00edmu prohlubov\u00e1n\u00ed) [15].<\/p>\n

V\u00a0z\u00e1sad\u011b existuj\u00ed dv\u011b z\u00e1kladn\u00ed konstrukce JET za\u0159\u00edzen\u00ed. T\u00edm star\u0161\u00edm je JET za\u0159\u00edzen\u00ed, je\u017e je p\u0159ibli\u017en\u011b 1\u00a0metr vysok\u00e9 s\u00a0pr\u016fm\u011brem z\u00e1kladov\u00e9ho prstence 300 mm a\u00a0pr\u016fm\u011brem trysky 6,4 mm [16]. P\u016fvodn\u00ed JET za\u0159\u00edzen\u00ed je tak\u00e9 vybaveno z\u00e1sobn\u00edkem na vodu, pomoc\u00ed kter\u00e9ho se v\u00a0syst\u00e9mu udr\u017euje konstantn\u00ed tlak na trysce. Nov\u011bj\u0161\u00ed a\u00a0men\u0161\u00ed varianta za\u0159\u00edzen\u00ed, Mini-JET, je asi 0,5 metru vysok\u00e1, s\u00a0pr\u016fm\u011brem z\u00e1kladov\u00e9ho prstence 100 mm a\u00a0pr\u016fm\u011brem trysky 3,2 mm [17, 18]. Za\u0159\u00edzen\u00ed nen\u00ed osazeno z\u00e1sobn\u00edkem na vodu, n\u00fdbr\u017e je z\u00e1visl\u00e9 na extern\u00edm p\u0159\u00edvodu vody. Ob\u011b konstruk\u010dn\u00ed varianty se pou\u017e\u00edvaj\u00ed jak za jasn\u011b definovan\u00fdch podm\u00ednek v\u00a0laborato\u0159i, tak i\u00a0pro ter\u00e9nn\u00ed m\u011b\u0159en\u00ed.<\/p>\n

Mini-JET za\u0159\u00edzen\u00ed<\/h2>\n

Jde o\u00a0men\u0161\u00ed verzi p\u016fvodn\u00edho za\u0159\u00edzen\u00ed JET. P\u0159\u00edmou p\u0159edlohou pro zde prezentovan\u00fd Mini-JET je za\u0159\u00edzen\u00ed, kter\u00e9 pro v\u00fdzkum eroze b\u0159ehov\u00fdch hran vodn\u00edch tok\u016f v\u00a0Tennessee (USA) pou\u017e\u00edvali Mahalder a\u00a0kol. [9]. Pro pot\u0159eby experiment\u016f na nesoudr\u017en\u00e9 ornici bylo za\u0159\u00edzen\u00ed upraveno. Modifikace spo\u010d\u00edv\u00e1 v\u00a0\u00faprav\u011b pr\u016fm\u011bru z\u00e1kladov\u00e9ho prstence, jen\u017e byl zv\u011bt\u0161en tak, aby p\u0159i erozi nesoudr\u017en\u00e9 ornice nedoch\u00e1zelo k\u00a0roz\u0161\u00ed\u0159en\u00ed erozn\u00edho kr\u00e1teru a\u017e k\u00a0prstenci (obr.\u00a01<\/em>). N\u00e1vrh t\u00e9to modifikace byl vytvo\u0159en na Kated\u0159e hydromeliorac\u00ed a\u00a0krajinn\u00e9ho in\u017een\u00fdrstv\u00ed \u010cVUT v\u00a0Praze. P\u0159\u00edstroj byl n\u00e1sledn\u011b vyroben na zak\u00e1zku firmou CS Plasting,\u00a0s.\u00a0r.\u00a0o. Druhou v\u00fdznamnou \u00fapravou je syst\u00e9m regulace tlaku vody, kter\u00fd umo\u017e\u0148uje nastaven\u00ed n\u00edzk\u00e9 kinetick\u00e9 energie vodn\u00edho paprsku.<\/p>\n\"\"<\/a>\n

Obr. 1. Modifikovan\u00e1 konstrukce za\u0159\u00edzen\u00ed Mini-JET
\nFig.\u00a01. Modified design of the Mini-JET device<\/h6>\n

Modifikovan\u00fd Mini-JET je schematicky, v\u010detn\u011b jednotliv\u00fdch komponent, uk\u00e1z\u00e1n na obr.\u00a02<\/em> a\u00a03<\/em>. Pot\u0159ebn\u00fd tlak vody je zaji\u0161\u0165ov\u00e1n elektrick\u00fdm \u010derpadlem. N\u00e1sledn\u00e1 \u00faprava tlaku na trysce se prov\u00e1d\u00ed pomoc\u00ed ventilu s\u00a0jemnou regulac\u00ed\u00a0(1), kter\u00fd je um\u00edst\u011bn na p\u0159\u00edvodn\u00ed armatu\u0159e (2). Tlak vody je kontrolov\u00e1n pomoc\u00ed manometru (3), um\u00edst\u011bn\u00e9m v\u00a0horn\u00ed \u010d\u00e1sti p\u0159\u00edstroje. Jako u\u00a0p\u016fvodn\u00ed konstrukce JET je za\u0159\u00edzen\u00ed vybaveno oto\u010dnou deskou (4), na n\u00ed\u017e je p\u0159ipevn\u011bna tryska (5) spole\u010dn\u011b s\u00a0m\u011b\u0159idlem hloubky erozn\u00edho kr\u00e1teru (6). Pomoc\u00ed ot\u00e1\u010den\u00ed je za\u0159\u00edzen\u00ed v\u00a0poloze pracovn\u00ed (obr.\u00a02<\/em>), nebo \u010dtec\u00ed (obr.\u00a03<\/em>). Z\u00e1kladov\u00fd prstenec (7) je odd\u011bliteln\u00fd od zaplavovac\u00ed n\u00e1dr\u017ee (8) a\u00a0b\u011bhem experimentu je kotven\u00fd k\u00a0zaplavovac\u00ed n\u00e1dr\u017ei pomoc\u00ed kovov\u00fdch svorek (9).<\/p>\n

\"\"<\/a><\/h6>\n
Obr.\u00a02. Sch\u00e9ma za\u0159\u00edzen\u00ed Mini-JET\u00a0\u2013 pracovn\u00ed poloha
\nFig.\u00a02. Schema of the Mini-JET device\u00a0\u2013 working position<\/h6>\n

Kalibrace za\u0159\u00edzen\u00ed<\/h2>\n

Pro ka\u017ed\u00fd konkr\u00e9tn\u00ed p\u0159\u00edstroj je t\u0159eba stanovit kalibra\u010dn\u00ed koeficient, kter\u00fd je n\u00e1sledn\u011b pou\u017eit pro v\u00fdpo\u010dty erozn\u00edch parametr\u016f [19]. Kalibra\u010dn\u00ed koeficient odpov\u00edd\u00e1 ztr\u00e1t\u00e1m v\u00a0hydraulick\u00fdch komponent\u00e1ch za\u0159\u00edzen\u00ed, je\u017e jsou specifick\u00e9 pro ka\u017ed\u00fd v\u00fdrobek podle jednotliv\u00fdch armatur, jejich parametr\u016f a\u00a0pou\u017eit\u00fdch materi\u00e1l\u016f (za\u0159\u00edzen\u00ed se nevyr\u00e1b\u00ed s\u00e9riov\u011b a\u00a0ka\u017ed\u00fd kus je origin\u00e1lem). Pro v\u00fdpo\u010det kalibra\u010dn\u00edho koeficientu je pot\u0159eba zn\u00e1t pr\u016ftok tryskou p\u0159i\u00a0r\u016fzn\u00fdch pracovn\u00edch tlac\u00edch. V\u00fdpo\u010det kalibra\u010dn\u00edho koeficientu byl proveden podle Mahaldera [19].<\/p>\n

Dal\u0161\u00edm pot\u0159ebn\u00fdm parametrem je tzv. teoretick\u00fd pr\u016ftok Qteo<\/sub>, kter\u00fd p\u0159edstavuje maxim\u00e1ln\u00ed pr\u016ftok p\u0159\u00edstrojem p\u0159i nulov\u00fdch ztr\u00e1t\u00e1ch:<\/p>\n\"\"<\/a>\n\n\n\n\n\n\n
kde<\/td>\nQteo<\/sub><\/em><\/td>\nje<\/td>\nteoretick\u00fd pr\u016ftok [m3<\/sup>.s-1<\/sup>]<\/td>\n<\/tr>\n
<\/td>\nA<\/em><\/td>\n<\/td>\npr\u016f\u0159ezov\u00e1 plocha trysky [m2<\/sup>]<\/td>\n<\/tr>\n
<\/td>\n\u00a0g<\/em><\/td>\n<\/td>\ngravita\u010dn\u00ed zrychlen\u00ed [m.s-2<\/sup>]<\/td>\n<\/tr>\n
<\/td>\n h<\/em><\/td>\n<\/td>\ntlakov\u00e1 v\u00fd\u0161ka [m v. sl.]<\/td>\n<\/tr>\n<\/tbody>\n<\/table>\n

V\u00fdsledky kalibrace jsou zn\u00e1zorn\u011bny graficky (obr.\u00a04<\/em>), kde na ose x jsou hodnoty vypo\u010dten\u00e9ho teoretick\u00e9ho pr\u016ftoku a\u00a0na ose y jsou hodnoty m\u011b\u0159en\u00e9ho pr\u016ftoku. Jednotliv\u00fdmi body byla prolo\u017eena p\u0159\u00edmka, jej\u00ed\u017e sm\u011brnice odpov\u00edd\u00e1 kalibra\u010dn\u00edmu koeficientu [19].<\/p>\n

Experiment\u00e1ln\u00ed lokalita a ter\u00e9nn\u00ed m\u011b\u0159en\u00ed<\/h2>\n

V\u0161echny Mini-JET experimenty byly provedeny na experiment\u00e1ln\u00edch ploch\u00e1ch u\u00a0obce \u0158isuty. Obec \u0158isuty le\u017e\u00ed v\u00a0okrese Kladno asi 5 km z\u00e1padn\u011b od Slan\u00e9ho. Experiment\u00e1ln\u00ed plochy se nach\u00e1zej\u00ed v\u00a0nadmo\u0159sk\u00e9 v\u00fd\u0161ce cca 320\u00a0m\u00a0n.\u00a0m. Klima je such\u00e9 a\u00a0tepl\u00e9, s\u00a0m\u00edrnou zimou a\u00a0velmi kr\u00e1tk\u00fdm trv\u00e1n\u00edm sn\u011bhov\u00e9 pokr\u00fdvky. Pr\u016fm\u011brn\u00e1 ro\u010dn\u00ed teplota se tu pohybuje mezi 8 a\u00a09 \u00b0C. Pr\u016fm\u011brn\u00fd ro\u010dn\u00ed sr\u00e1\u017ekov\u00fd \u00fahrn b\u00fdv\u00e1 okolo 500\u00a0mm. P\u016fdn\u00edm typem je kambizem mod\u00e1ln\u00ed (BPEJ 1.33.11), z\u00a0hlediska zrnitostn\u00edho slo\u017een\u00ed jde o\u00a0prachovitou hl\u00ednu (tab.\u00a01<\/em>). Experiment\u00e1ln\u00ed m\u011b\u0159en\u00ed se za\u0159\u00edzen\u00edm Mini-JET prob\u00edh\u00e1 n\u00e1razov\u011b od l\u00e9ta roku 2020.<\/p>\n

C\u00edlem ter\u00e9nn\u00edch m\u011b\u0159en\u00ed bylo otestovat za\u0159\u00edzen\u00ed v\u00a0poln\u00edch podm\u00ednk\u00e1ch, vybrat nejvhodn\u011bj\u0161\u00ed provozn\u00ed tlak pro dan\u00e9 podm\u00ednky a\u00a0zjistit, zda v\u00fdsledky budou pou\u017eiteln\u00e9 pro stanoven\u00ed erozn\u00edch parametr\u016f testovan\u00e9 p\u016fdy. Jeliko\u017e metodika v\u00fdpo\u010dtu erozn\u00edch parametr\u016f po\u010d\u00edt\u00e1 s\u00a0homogenn\u00edm p\u016fdn\u00edm prost\u0159ed\u00edm, byly zvoleny dva typy p\u016fdn\u00edho povrchu, kter\u00e9 se nejv\u00edce p\u0159ibli\u017euj\u00ed homogenn\u00edmu prost\u0159ed\u00ed.<\/p>\n

Na experiment\u00e1ln\u00ed plo\u0161e \u010d. 1 se nach\u00e1zel tzv. \u010derstv\u011b vytvo\u0159en\u00fd v\u00e1lcovan\u00fd \u00fahor<\/strong> (obr.\u00a05<\/em>) o\u00a0pr\u016fm\u011brn\u00e9 objemov\u00e9 hmotnosti cca 1,35\u00a0g.cm-3<\/sup>. Jde o\u00a0p\u016fdn\u00ed povrch, kter\u00fd je srovn\u00e1vac\u00edm stavem pro m\u011b\u0159en\u00ed smyvu b\u011bhem kampan\u00ed s\u00a0de\u0161\u0165ov\u00fdm simul\u00e1torem pro ur\u010dov\u00e1n\u00ed C-faktoru [20]. Povrch je p\u0159ipravov\u00e1n v\u00a0den simulace nakyp\u0159en\u00edm p\u016fdy kultiv\u00e1torem, srovn\u00e1n\u00edm povrchu hr\u00e1b\u011bmi a\u00a0n\u00e1sledn\u00fdm uv\u00e1lcov\u00e1n\u00edm.<\/p>\n

Na experiment\u00e1ln\u00ed plo\u0161e \u010d. 2 se nach\u00e1zel povrch po b\u011b\u017en\u00e9 p\u0159\u00edprav\u011b pozemku na se\u0165ov\u00e9 lo\u017ee<\/strong>. P\u0159\u00edprava spo\u010d\u00edvala v\u00a0orb\u011b do hloubky 26 cm, podm\u00edtce do hloubky 20 cm a\u00a0v\u00a0set\u00ed \u017eita po sp\u00e1dnici. Tento povrch je soudr\u017en\u011bj\u0161\u00ed ne\u017e v\u00fd\u0161e uveden\u00fd v\u00e1lcovan\u00fd \u00fahor, proto\u017ee od orby do prvn\u00edho Mini-JET experimentu uplynulo 22 dn\u00ed, b\u011bhem nich\u017e tvo\u0159il sr\u00e1\u017ekov\u00fd \u00fahrn 35 mm, d\u00edky \u010demu\u017e se p\u016fda stala kompaktn\u011bj\u0161\u00ed (obr.\u00a05<\/em>). To dokazuje i\u00a0objemov\u00e1 hmotnost p\u016fdy (1,81\u20131,85\u00a0g.cm-3<\/sup>), kter\u00e1 je vy\u0161\u0161\u00ed ne\u017e u v\u00e1lcovan\u00e9ho \u00fahoru (tab.\u00a01<\/em>).<\/p>\n

Celkem bylo provedeno 75 experiment\u016f, z\u00a0toho 13 na v\u00e1lcovan\u00e9m \u00fahoru a\u00a062 na se\u0165ov\u00e9m lo\u017ei. Na v\u00e1lcovan\u00e9m \u00fahoru bylo uskute\u010dn\u011bno v\u00fdrazn\u011b m\u00e9n\u011b simulac\u00ed, jeliko\u017e experiment\u00e1ln\u00ed m\u011b\u0159en\u00ed s\u00a0p\u0159\u00edstrojem za\u010dalo v\u00a0l\u00e9t\u011b 2020 a\u00a0v\u011bt\u0161ina m\u011b\u0159en\u00ed prob\u00edhala a\u017e na podzim 2020. V\u00a0tomto obdob\u00ed je ji\u017e velmi obt\u00ed\u017en\u00e9 p\u0159ipravit referen\u010dn\u00ed plochu (p\u0159edev\u0161\u00edm kv\u016fli vysok\u00e9 vlhkosti p\u016fdy). Druh\u00fdm d\u016fvodem je pom\u011brn\u011b slo\u017eit\u00e9 prov\u00e1d\u011bn\u00ed experimentu na nakyp\u0159en\u00e9m \u00fahoru, \u00fasp\u011b\u0161nost simulac\u00ed na utu\u017een\u011bj\u0161\u00edm se\u0165ov\u00e9m lo\u017ei byla vy\u0161\u0161\u00ed.<\/p>\n\"\"<\/a>\n

Obr.\u00a03. Sch\u00e9ma za\u0159\u00edzen\u00ed Mini-JET\u00a0\u2013 \u010dtec\u00ed poloha
\nFig.\u00a03. Schema of the Mini-JET device\u00a0\u2013 reading position<\/h6>\n\"\"<\/a>\n
Obr.\u00a04. Ur\u010den\u00ed kalibra\u010dn\u00edho koeficientu, kter\u00fd v\u00a0p\u0159\u00edpad\u011b konkr\u00e9tn\u00edho za\u0159\u00edzen\u00ed odpov\u00edd\u00e1 sm\u011brnici p\u0159\u00edmky 0,696
\nFig.\u00a04. Determination of the calibration coefficient, which in the case of the specific device corresponds a\u00a0value of 0.696<\/h6>\n
Tab.\u00a01. P\u016fdn\u00ed charakteristiky testovan\u00fdch povrch\u016f
\n<\/em>Tab.\u00a01. Soil characteristics of tested surfaces<\/em><\/h5>\n\"\"<\/a>\n

Cel\u00fd syst\u00e9m za\u0159\u00edzen\u00ed Mini-JET byl p\u0159ed experimentem zkompletov\u00e1n a\u00a0\u0159\u00e1dn\u011b odvzdu\u0161n\u011bn. U\u00a0n\u00e1sledn\u00e9ho v\u00fdb\u011bru vhodn\u00e9ho m\u00edsta pro simulaci bylo pot\u0159eba d\u00e1t si pozor na p\u0159\u00edtomnost p\u0159edm\u011bt\u016f, kter\u00e9 by mohly naru\u0161it tvorbu erozn\u00edho kr\u00e1teru. P\u0159edn\u011b to jsou kameny, rostlinn\u00e9 zbytky, ko\u0159eny atd. Tyto p\u0159edm\u011bty ovliv\u0148uj\u00ed tvorbu erozn\u00edho kr\u00e1teru a\u00a0m\u011b\u0159en\u00ed znehodnocuj\u00ed. Z\u00e1kladov\u00fd prstenec mus\u00ed b\u00fdt instalov\u00e1n do p\u016fdy vodorovn\u011b. P\u0159i velk\u00e9m sklonu by nemusela b\u00fdt tryska pono\u0159ena ve vod\u011b, tud\u00ed\u017e by neplatily vztahy pro n\u00e1sledn\u00e9 v\u00fdpo\u010dty erozn\u00edch parametr\u016f. D\u00e1le byly odebr\u00e1ny neporu\u0161en\u00e9 p\u016fdn\u00ed vzorky pro stanoven\u00ed fyzik\u00e1ln\u00edch p\u016fdn\u00edch charakteristik.<\/p>\n

C\u00edlem m\u011b\u0159en\u00ed je co nejp\u0159esn\u011bji zaznamenat pr\u016fb\u011bh tvorby erozn\u00edho kr\u00e1teru v\u00a0\u010dase. D\u016fle\u017eit\u00e9 je nastaven\u00ed vhodn\u00e9ho tlaku vody. Pokud by byl p\u0159\u00edli\u0161 vysok\u00fd, kr\u00e1ter se v\u00a0nesoudr\u017en\u00e9 p\u016fd\u011b vytvo\u0159\u00ed okam\u017eit\u011b. Naopak pokud by byl tlak p\u0159\u00edli\u0161 n\u00edzk\u00fd, erozn\u00ed kr\u00e1ter se nevytvo\u0159\u00ed. Pro v\u00e1lcovan\u00fd \u00fahor byl pou\u017eit tlak okolo 1\u00a0psi (6,9 kPa) a\u00a0pro se\u0165ov\u00e9 l\u016f\u017eko byly nastaveny tlaky mezi 3 a\u00a04 psi (20,7\u00a0a\u00a027,6\u00a0kPa). Pou\u017eit\u00e9 tlaky vody byly ur\u010deny p\u0159edev\u0161\u00edm na z\u00e1klad\u011b zku\u0161enost\u00ed oper\u00e1tora za\u0159\u00edzen\u00ed. Jeliko\u017e v\u00e1lcovan\u00fd \u00fahor je m\u00e9n\u011b soudr\u017en\u00fd ne\u017e se\u0165ov\u00e9 lo\u017ee, bylo pot\u0159eba pou\u017e\u00edt na v\u00e1lcovan\u00fd \u00fahor podstatn\u011b ni\u017e\u0161\u00ed tlak ne\u017e na se\u0165ov\u00e9 lo\u017ee, aby bylo mo\u017en\u00e9 zaznamenat pr\u016fb\u011bh tvorby erozn\u00edho kr\u00e1teru v\u00a0\u010dase. P\u0159i vysok\u00e9m tlaku je kr\u00e1ter vytvo\u0159en okam\u017eit\u011b. Vodn\u00ed paprsek se na p\u016fdn\u00ed povrch pou\u0161t\u011bl v\u00a0intervalech, je\u017e se s\u00a0prohlubov\u00e1n\u00edm erozn\u00edho kr\u00e1teru prodlu\u017eovaly. Mezi aplikacemi vodn\u00edho paprsku (obr.\u00a02<\/em>) se p\u0159\u00edstroj ot\u00e1\u010del do \u010dtec\u00ed polohy (obr.\u00a03<\/em>) a\u00a0m\u011b\u0159il se pr\u016fb\u011bh tvorby kr\u00e1teru, respektive jeho hloubka. Jako po\u010d\u00e1te\u010dn\u00ed doba aplikace proudu vody byla zvolena hodnota 5 s. M\u011b\u0159en\u00ed bylo ukon\u010deno, kdy\u017e se p\u0159i posledn\u00edch t\u0159ech m\u011b\u0159en\u00edch o\u00a0d\u00e9lce minim\u00e1ln\u011b 30\u00a0s\u00a0hloubka erozn\u00edho kr\u00e1teru nezv\u011bt\u0161ovala (obr.\u00a06<\/em>). P\u0159i m\u011b\u0159en\u00ed hloubky erozn\u00edho kr\u00e1teru bylo pot\u0159eba spou\u0161t\u011bt m\u011b\u0159idlo opatrn\u011b. P\u0159i samovoln\u00e9m pu\u0161t\u011bn\u00ed by m\u011b\u0159idlo mohlo prohloubit kr\u00e1ter, a\u00a0mohlo by tak doj\u00edt ke zkreslen\u00ed v\u00fdsledk\u016f.<\/p>\n

V\u00fdpo\u010det erozn\u00edch parametr\u016f<\/h2>\n

Pro v\u00fdpo\u010det kritick\u00e9ho te\u010dn\u00e9ho nap\u011bt\u00ed \u03c4<\/em>c<\/sub> a\u00a0koeficientu erodovatelnosti k<\/em>d<\/sub> byl pou\u017eit n\u00e1stroj \u201eJet Erosion Test Spreadsheet Tool\u201c [19]. Tento tabulkov\u00fd n\u00e1stroj (MS Excel) vyvinuli Hanson a\u00a0Cook [11]. Do n\u00e1stroje pou\u017eili rovnice, kter\u00e9 stanov\u00ed kritick\u00e9 te\u010dn\u00e9 nap\u011bt\u00ed \u03c4<\/em>c<\/sub> na z\u00e1klad\u011b maxim\u00e1ln\u00edho prohlouben\u00ed erozn\u00edho kr\u00e1teru.<\/p>\n\"\"<\/a>\n

Obr.\u00a05. V\u00e1lcovan\u00fd \u00fahor na experiment\u00e1ln\u00ed plo\u0161e \u010d. 1 (vlevo) a\u00a0se\u0165ov\u00e9 l\u016f\u017eko na experiment\u00e1ln\u00ed plo\u0161e \u010d. 2 (vpravo)
\nFig.\u00a05. Fallow on experimental area No. 1 (left) and seedbed on experimental area No. 2 (right)<\/h6>\n\"\"<\/a>\n
Obr.\u00a06. Erozn\u00ed kr\u00e1ter po simulaci
\nFig.\u00a06. Erosion crater after simulation<\/h6>\n

Koeficient erodovatelnosti k<\/em>d<\/sub> je pot\u00e9 stanoven pomoc\u00ed p\u0159edem vypo\u010d\u00edtan\u00e9ho kritick\u00e9ho te\u010dn\u00e9ho nap\u011bt\u00ed, bezrozm\u011brn\u00e9 funkce \u010dasu T* a\u00a0bezrozm\u011brn\u00e9 funkce hloubky J* [11]. Tento n\u00e1stroj byl n\u00e1sledn\u011b je\u0161t\u011b n\u011bkolikr\u00e1t vylep\u0161en [10, 19], byly do n\u011bj p\u0159id\u00e1ny alternativn\u00ed metody stanoven\u00ed erozn\u00edch parametr\u016f. Jedn\u00edm z\u00a0p\u0159\u00edstup\u016f \u0159e\u0161en\u00ed je tzv. Blaisdellova metoda (BM), v\u00a0n\u00ed\u017e se erozn\u00ed parametry po\u010d\u00edtaj\u00ed na z\u00e1klad\u011b dat o\u00a0hloubce a\u00a0\u010dasu, kter\u00e9 se prokl\u00e1daj\u00ed hyperbolickou funkc\u00ed [21]. Zbyl\u00e9 dv\u011b metody \u201eScour depth\u201c a\u00a0Itera\u010dn\u00ed jsou variacemi Blaisdellovy metody. U\u00a0Itera\u010dn\u00ed metody jsou zpo\u010d\u00e1tku erozn\u00ed parametry \u03c4c<\/sub> a\u00a0kd<\/sub> odhadnuty pomoc\u00ed Blaisdellovy metody, parametry erodibility jsou \u0159e\u0161eny itera\u010dn\u011b. C\u00edlovou funkc\u00ed pro tuto Itera\u010dn\u00ed metodu je minimalizace chyby mezi m\u011b\u0159en\u00fdm a\u00a0predikovan\u00fdm \u010dasem. Je zde ov\u0161em horn\u00ed hranice \u03c4c<\/sub>, aby se zabr\u00e1nilo p\u0159ekro\u010den\u00ed rovnov\u00e1\u017en\u00e9 hloubky. V\u00a0metod\u011b \u201eScour depth\u201c jsou erozn\u00ed parametry tak\u00e9 \u0159e\u0161eny itera\u010dn\u011b. C\u00edlovou funkc\u00ed pro tuto metodu je minimalizace chyby mezi nam\u011b\u0159en\u00fdmi hloubkami a\u00a0predikovan\u00fdmi \u00fadaji o\u00a0hloubce. V\u00fdsledky t\u00e9to metody ukazuj\u00ed lep\u0161\u00ed p\u0159ibl\u00ed\u017een\u00ed nam\u011b\u0159en\u00fdm hodnot\u00e1m hloubek, ale hodnoty koeficientu erodovatelnosti mohou b\u00fdt v\u00a0n\u011bkter\u00fdch p\u0159\u00edpadech nadhodnocov\u00e1ny [9].<\/p>\n

Pro p\u0159\u00edpad nesoudr\u017en\u00fdch p\u016fd byla pou\u017eita metoda \u201eScour depth\u201c, jeliko\u017e pomoc\u00ed n\u00ed se pr\u016fb\u011bhy nam\u011b\u0159en\u00fdch hloubek erozn\u00edch kr\u00e1ter\u016f nejv\u00edce p\u0159ibli\u017euj\u00ed predikovan\u00e9mu pr\u016fb\u011bhu hloubky. Jednotliv\u00e9 metody vyhodnocen\u00ed Mini-JET experiment\u016f jsou pops\u00e1ny v\u00a0prac\u00edch [9, 10, 21].<\/p>\n

P\u0159ed v\u00fdpo\u010dty byly do v\u00fdpo\u010detn\u00edho n\u00e1stroje zad\u00e1ny parametry za\u0159\u00edzen\u00ed: pr\u016fm\u011br trysky 3,2\u00a0mm a\u00a0hodnota kalibra\u010dn\u00edho koeficientu 0,696. N\u00e1sledn\u011b byly vypo\u010dteny hodnoty erozn\u00edch parametr\u016f. Ze 75 simulac\u00ed bylo p\u0159i ur\u010dov\u00e1n\u00ed erodovatelnosti 23 simulac\u00ed vy\u0159azeno. D\u016fvodem bylo nerovnom\u011brn\u00e9 prohlubov\u00e1n\u00ed kr\u00e1teru, zp\u016fsoben\u00e9 nehomogenitou p\u016fdn\u00edho prost\u0159ed\u00ed, kv\u016fli kter\u00e9mu pr\u016fb\u011bh hloubky kr\u00e1teru neodpov\u00eddal v\u00fdpo\u010detn\u00ed metod\u011b \u201eScour depth\u201c.<\/p>\n

V\u00ddSLEDKY<\/h2>\n

Z\u00a0pou\u017eit\u00fdch simulac\u00ed byly vypo\u010dteny erozn\u00ed parametry, je\u017e jsou uvedeny v\u00a0tabulk\u00e1ch n\u00ed\u017ee (tab.\u00a02, tab.\u00a03<\/em>).<\/p>\n

Tab.\u00a02. V\u00fdsledn\u00e9 hodnoty kritick\u00e9ho te\u010dn\u00e9ho nap\u011bt\u00ed
\n<\/em>Tab.\u00a02. Measured values of critical shear stress<\/em><\/h5>\n\"\"<\/a>\n

Vypo\u010dten\u00e9 hodnoty pr\u016fm\u011brn\u00e9ho kritick\u00e9ho te\u010dn\u00e9ho nap\u011bt\u00ed pro povrchy v\u00e1lcovan\u00e9ho \u00fahoru se pohybuj\u00ed od 1,2 Pa do 1,5 Pa (tab.\u00a02<\/em>). Variabilita t\u011bchto hodnot je n\u00edzk\u00e1 (sm\u011brodatn\u00e1 odchylka 0,2 Pa). Tato variabilita je pravd\u011bpodobn\u011b zp\u016fsobena drobn\u00fdmi rozd\u00edly mezi p\u016fdn\u00edmi povrchy, jako jsou rozd\u00edln\u00e1 objemov\u00e1 hmotnost, po\u010d\u00e1te\u010dn\u00ed vlhkost \u010di r\u016fzn\u00e1 stabilita p\u016fdn\u00edch agreg\u00e1t\u016f. Jeliko\u017e u\u00a0povrchu v\u00e1lcovan\u00e9ho \u00fahoru nebyly m\u011b\u0159eny hodnoty stability p\u016fdn\u00edch agreg\u00e1t\u016f a\u00a0obsahu organick\u00e9ho uhl\u00edku, nelze jednozna\u010dn\u011b ur\u010dit d\u016fvod variability. V\u00a0neposledn\u00ed \u0159ad\u011b m\u016f\u017ee b\u00fdt m\u00edrn\u00e1 variabilita zp\u016fsobena procesn\u00edmi chybami, kter\u00e9 vznikly b\u011bhem simulac\u00ed a\u00a0vyhodnocen\u00ed.<\/p>\n

Vypo\u010dten\u00e9 hodnoty pr\u016fm\u011brn\u00e9ho kritick\u00e9ho te\u010dn\u00e9ho nap\u011bt\u00ed pro povrchy se\u0165ov\u00e9ho lo\u017ee dosahuj\u00ed vy\u0161\u0161\u00edch hodnot (5,5\u20136,5 Pa) ne\u017e u v\u00e1lcovan\u00e9ho \u00fahoru. To je zp\u016fsobeno p\u0159edev\u0161\u00edm vy\u0161\u0161\u00ed objemovou hmotnost\u00ed. U se\u0165ov\u00e9ho lo\u017ee byla zaznamen\u00e1na vy\u0161\u0161\u00ed variabilita v\u00fdsledn\u00fdch hodnot (sm\u011brodatn\u00e1 odchylka 1,5\u20131,7 Pa). Tato variabilita je pravd\u011bpodobn\u011b zp\u016fsobena stejn\u00fdmi vlivy jako v p\u0159ede\u0161l\u00e9m p\u0159\u00edpad\u011b, u se\u0165ov\u00e9ho lo\u017ee jsou v\u0161ak prostorov\u011b je\u0161t\u011b v\u00fdrazn\u011bj\u0161\u00ed.<\/p>\n

Tab.\u00a03. V\u00fdsledn\u00e9 hodnoty koeficientu erodovatelnosti
\n<\/em>Tab.\u00a03. Measured values of the erodibility coefficient<\/em><\/h5>\n\n\n\n\n\n\n\n\n\n
Povrch<\/strong><\/td>\nKoeficient erodovatelnosti [cm3<\/sup>.N-1<\/sup>.s-1<\/sup>]<\/strong><\/td>\n\u00a0<\/strong><\/td>\n\u00a0<\/strong><\/td>\n\u00a0<\/strong><\/td>\n<\/tr>\n
Min.<\/strong><\/td>\nMax.<\/strong><\/td>\nPr\u016fm\u011br<\/strong><\/td>\nSm. odch.<\/strong><\/td>\n<\/tr>\n
V\u00e1lcovan\u00fd \u00fahor (8. 7. 2020)<\/td>\n182,5<\/td>\n1594,0<\/td>\n770,0<\/td>\n600,0<\/td>\n<\/tr>\n
V\u00e1lcovan\u00fd \u00fahor (10. 9. 2020)<\/td>\n448,5<\/td>\n1415,1<\/td>\n881,4<\/td>\n280,8<\/td>\n<\/tr>\n
Se\u0165ov\u00e9 lo\u017ee (21. 10. 2020)<\/td>\n19,2<\/td>\n424,2<\/td>\n121,2<\/td>\n132,6<\/td>\n<\/tr>\n
Se\u0165ov\u00e9 lo\u017ee (24. 10. 2020)<\/td>\n12,4<\/td>\n315,2<\/td>\n111,3<\/td>\n88,8<\/td>\n<\/tr>\n
Se\u0165ov\u00e9 lo\u017ee (25. 10. 2020)<\/td>\n8,2<\/td>\n621,0<\/td>\n148,8<\/td>\n183,1<\/td>\n<\/tr>\n<\/tbody>\n<\/table>\n

Pr\u016fm\u011brn\u00e9 hodnoty koeficientu erodovatelnosti pro v\u00e1lcovan\u00fd \u00fahor dosahuj\u00ed 770,0\u2013881,4 cm3<\/sup>.N-1<\/sup>.s-1<\/sup> a\u00a0vykazuj\u00ed vysokou variabilitu (tab.\u00a03<\/em>). D\u016fvodem variability jsou p\u0159edev\u0161\u00edm zna\u010dn\u00e1 nesoudr\u017enost p\u016fdy (p\u0159edem nakyp\u0159en\u00e1 a\u00a0uv\u00e1lcovan\u00e1) a\u00a0tak\u00e9 vysok\u00e1 citlivost koeficientu erodovatelnosti na zm\u011bny ve velmi n\u00edzk\u00fdch hodnot\u00e1ch kritick\u00e9ho te\u010dn\u00e9ho nap\u011bt\u00ed.<\/p>\n

Pr\u016fm\u011brn\u00e9 hodnoty koeficientu erodovatelnosti se\u0165ov\u00e9ho lo\u017ee jsou v\u00fdrazn\u011b ni\u017e\u0161\u00ed (111,3\u2013148,8 cm3<\/sup>.N-1<\/sup>.s-1<\/sup>), ale tak\u00e9 vykazuj\u00ed vysokou variabilitu. Jeliko\u017e je tato p\u016fda soudr\u017en\u011bj\u0161\u00ed, hodnoty koeficientu erodovatelnosti jsou ni\u017e\u0161\u00ed. P\u0159\u00ed\u010diny vysok\u00e9 variability jsou pravd\u011bpodobn\u011b stejn\u00e9 jako u\u00a0v\u00e1lcovan\u00e9ho \u00fahoru.<\/p>\n

DISKUZE<\/h2>\n

Pro otestov\u00e1n\u00ed modifikovan\u00e9ho za\u0159\u00edzen\u00ed Mini-JET byly vyu\u017eity dva typy p\u016fdn\u00edho povrchu. Byl to povrch v\u00e1lcovan\u00e9ho \u00fahoru o\u00a0objemov\u00e9 hmotnosti 1,35\u00a0g.cm-3 <\/sup>a\u00a0po\u010d\u00e1te\u010dn\u00ed objemov\u00e9 vlhkosti 19,5 %, a\u00a0povrch se\u0165ov\u00e9ho lo\u017ee o\u00a0objemov\u00e9 hmotnosti 1,83 g.cm-3<\/sup>, po\u010d\u00e1te\u010dn\u00ed vlhkosti 30,6\u00a0%, stabilit\u011b p\u016fdn\u00edch agreg\u00e1t\u016f 58,2\u00a0% a\u00a0obsahu organick\u00e9ho uhl\u00edku 1,53\u00a0%. P\u016fda byla klasifikov\u00e1na jako prachovit\u00e1 hl\u00edna (j\u00edl\u00a0\u2013 9,0 %, prach\u00a0\u2013 56,3 %, p\u00edsek\u00a0\u2013 34,7 %).<\/p>\n

Po experimentech byl proveden v\u00fdpo\u010det erozn\u00edch parametr\u016f. U\u00a0v\u00e1lcovan\u00e9ho \u00fahoru byla pr\u016fm\u011brn\u00e1 hodnota kritick\u00e9ho te\u010dn\u00e9ho nap\u011bt\u00ed 1,4 Pa se sm\u011brodatnou odchylkou 0,2 Pa a\u00a0pr\u016fm\u011brn\u00e1 hodnota koeficientu erodovatelnosti byla 825,7 cm3<\/sup>.N-1<\/sup>.s-1<\/sup> se sm\u011brodatnou odchylkou 440,4 cm3<\/sup>.N-1<\/sup>.s-1<\/sup>. Jeliko\u017e se v\u00a0t\u00e9to studii testovalo za\u0159\u00edzen\u00ed Mini-JET poprv\u00e9 na zna\u010dn\u011b nesoudr\u017en\u00e9 p\u016fd\u011b, nelze v\u00fdsledky s\u00a0jin\u00fdmi obdobn\u00fdmi m\u011b\u0159en\u00edmi p\u0159\u00edmo porovnat.<\/p>\n

P\u016fdn\u00ed povrch se\u0165ov\u00e9ho lo\u017ee byl soudr\u017en\u011bj\u0161\u00ed, pr\u016fm\u011brn\u00e1 hodnota kritick\u00e9ho te\u010dn\u00e9ho nap\u011bt\u00ed dosahovala 5,80\u00a0Pa, co\u017e je srovnateln\u00e9 s\u00a0m\u011b\u0159en\u00edm Mahaldera a\u00a0kol. [9], kte\u0159\u00ed testovali p\u016fdu o\u00a0objemov\u00e9 hmotnosti 1,80\u00a0g.cm-3<\/sup> a\u00a0vlhkosti okolo 30\u00a0%. P\u0159i pou\u017eit\u00ed metody \u201eScour depth\u201c Mahalder a\u00a0kol. [9] uv\u00e1d\u011bj\u00ed v\u00fdsledn\u00e9 pr\u016fm\u011brn\u00e9 kritick\u00e9 te\u010dn\u00e9 nap\u011bt\u00ed 6,9 Pa se sm\u011brodatnou odchylkou 3,8 Pa.<\/p>\n

Pr\u016fm\u011brn\u00e1 hodnota koeficientu erodovatelnosti byla 127,1 cm3<\/sup>.N-1<\/sup>.s-1<\/sup> se sm\u011brodatnou odchylkou 134,8 cm3<\/sup>.N-1<\/sup>.s-1<\/sup>. Mahalder a\u00a0kol. [9] uv\u00e1d\u00ed v\u00fdrazn\u011b ni\u017e\u0161\u00ed hodnotu, konkr\u00e9tn\u011b 12,3 cm3<\/sup>.N-1<\/sup>.s-1<\/sup> se sm\u011brodatnou odchylkou 13,0 cm3<\/sup>.N-1<\/sup>.s-1<\/sup>. Nesourodost v\u00fdsledk\u016f je zp\u016fsobena pravd\u011bpodobn\u011b t\u00edm, \u017ee dosavadn\u00ed studie [9\u201311] se v\u011bnovaly testov\u00e1n\u00edm za\u0159\u00edzen\u00ed na soudr\u017en\u00fdch p\u016fd\u00e1ch (zejm\u00e9na p\u016fdy na b\u0159ez\u00edch vodn\u00edch tok\u016f), oproti tomu tato studie testuje za\u0159\u00edzen\u00ed na nesoudr\u017en\u00fdch p\u016fd\u00e1ch. Nicm\u00e9n\u011b i zde dosahovala sm\u011brodatn\u00e1 odchylka m\u011b\u0159en\u00ed stejn\u00fdch \u0159\u00e1d\u016f jako nam\u011b\u0159en\u00e9 hodnoty koeficientu erodovatelnosti. Pomoc\u00ed metody \u201eScour depth\u201c testovali soudr\u017enost p\u016fdn\u00edho povrchu tak\u00e9 Daly a\u00a0kol. [10], kte\u0159\u00ed u\u00a0soudr\u017en\u00fdch p\u016fd zm\u011b\u0159ili kritick\u00e9 te\u010dn\u00e9 nap\u011bt\u00ed v\u00a0rozmez\u00ed 1,2\u201316,4 Pa a\u00a0koeficient erodovatelnosti 2,0\u2013210,8 cm3<\/sup>.N-1<\/sup>.s-1<\/sup>.<\/p>\n

Velk\u00e1 variabilita erozn\u00edch veli\u010din zji\u0161t\u011bn\u00e1 p\u0159i m\u011b\u0159en\u00edch se za\u0159\u00edzen\u00edmi typu JET nebo Mini-JET je tak charakteristick\u00e1 pro v\u0161echny typy p\u016fdn\u00edch povrch\u016f. P\u0159esto jsou na r\u016fzn\u00fdch p\u016fd\u00e1ch s\u00a0odli\u0161nou soudr\u017enost\u00ed prokazateln\u011b nam\u011b\u0159eny hodnoty erodovatelnosti, je\u017e jsou vyu\u017eiteln\u00e9 pro implementaci v\u00a0erozn\u00edch modelech. Na z\u00e1klad\u011b proveden\u00fdch test\u016f lze proto konstatovat, \u017ee metodu lze uplatnit i\u00a0na zem\u011bd\u011blsk\u00fdch p\u016fd\u00e1ch. Pro z\u00edsk\u00e1n\u00ed relevantn\u00edch hodnot erodovatelnosti je v\u0161ak t\u0159eba prov\u00e9st v\u017edy dostate\u010dn\u00fd po\u010det replikac\u00ed, aby i\u00a0p\u0159es variabilitu nam\u011b\u0159en\u00fdch hodnot byly pr\u016fm\u011brn\u00e9 hodnoty erodovatelnosti statisticky jasn\u011b prokazateln\u00e9.<\/p>\n

Zde jsou uvedeny nejistoty a\u00a0chyby, kter\u00e9 mohly vzniknout p\u0159i samotn\u00e9m ter\u00e9nn\u00edm m\u011b\u0159en\u00ed nebo p\u0159i pozd\u011bj\u0161\u00edch v\u00fdpo\u010dtech:<\/p>\n

    \n
  • Nedokonal\u00e9 odvzdu\u0161n\u011bn\u00ed syst\u00e9mu<\/strong>\u00a0\u2013 p\u0159i nedostate\u010dn\u00e9m odvzdu\u0161n\u011bn\u00ed doch\u00e1z\u00ed k\u00a0nespr\u00e1vn\u00e9mu m\u011b\u0159en\u00ed manometru a\u00a0hodnoty nemusej\u00ed odpov\u00eddat skute\u010dnosti. To se negativn\u011b prom\u00edtne do vypo\u010dten\u00fdch erozn\u00edch koeficient\u016f. Tato chyba byla kontrolou syst\u00e9mu minimalizov\u00e1na.<\/li>\n
  • Nehomogenn\u00ed p\u016fdn\u00ed prost\u0159ed\u00ed<\/strong> \u2013 metodika v\u00fdpo\u010dtu erozn\u00edch parametr\u016f p\u0159edpokl\u00e1d\u00e1 homogenn\u00ed p\u016fdn\u00ed prost\u0159ed\u00ed v m\u00edst\u011b simulace. Pokud p\u016fdn\u00ed prost\u0159ed\u00ed nen\u00ed homogenn\u00ed, nap\u0159. v\u00fdskytem preferen\u010dn\u00edch makrop\u00f3r\u016f (hlodavci aj.), doch\u00e1z\u00ed k ovlivn\u011bn\u00ed v\u00fdsledn\u00e9 hodnoty erozn\u00edch parametr\u016f.<\/li>\n
  • Ovl\u00e1d\u00e1n\u00ed hloubkov\u00e9ho m\u011b\u0159idla<\/strong>\u00a0\u2013 pokud p\u0159i m\u011b\u0159en\u00ed dojde k\u00a0p\u0159\u00edli\u0161 rychl\u00e9mu spu\u0161t\u011bn\u00ed m\u011b\u0159idla do kr\u00e1teru, m\u011b\u0159idlo se do p\u016fdy zabo\u0159\u00ed. \u010cten\u00ed je potom nadhodnocen\u00e9 a\u00a0dno kr\u00e1teru je pro n\u00e1sleduj\u00edc\u00ed \u010dasov\u00fd \u00fasek m\u011b\u0159en\u00ed znehodnoceno. V\u017edy je pot\u0159eba hloubkov\u00e9 m\u011b\u0159idlo spou\u0161t\u011bt do erozn\u00edho kr\u00e1teru pomalu a\u00a0opatrn\u011b.<\/li>\n
  • V\u00fdskyt ne\u017e\u00e1douc\u00edho p\u0159edm\u011btu v p\u016fd\u011b<\/strong> \u2013 jestli\u017ee se p\u0159\u00edmo v erozn\u00edm kr\u00e1teru vyskytne ne\u017e\u00e1douc\u00ed p\u0159edm\u011bt, jako jsou nap\u0159\u00edklad kameny \u010di ko\u0159eny, prohlubov\u00e1n\u00ed kr\u00e1teru se zastav\u00ed.<\/li>\n
  • Chybn\u011b ur\u010den\u00fd kalibra\u010dn\u00ed koeficient za\u0159\u00edzen\u00ed<\/strong> \u2013 nespr\u00e1vn\u011b stanoven\u00fd kalibra\u010dn\u00ed koeficient pro konkr\u00e9tn\u00ed za\u0159\u00edzen\u00ed vede k chybn\u00e9mu v\u00fdpo\u010dtu erozn\u00edch charakteristik.<\/li>\n<\/ul>\n

    Z\u00c1V\u011aR<\/h2>\n

    C\u00edlem\u00a0t\u00e9to pr\u00e1ce bylo stanovit erodovatelnost nesoudr\u017en\u00fdch zem\u011bd\u011blsk\u00fdch p\u016fd pomoc\u00ed m\u011b\u0159en\u00ed kritick\u00e9ho te\u010dn\u00e9ho nap\u011bt\u00ed. Pro ur\u010den\u00ed kritick\u00e9ho nap\u011bt\u00ed byla vyu\u017eita inovativn\u00ed technika zalo\u017een\u00e1 na tzv. \u201eJet Erosion Testu\u201c, erozn\u00ed experimenty byly prov\u00e1d\u011bny s\u00a0vyu\u017eit\u00edm modifikovan\u00e9ho za\u0159\u00edzen\u00ed Mini-JET. U\u00a0testovan\u00e9ho p\u0159\u00edstroje byla provedena kalibrace pro stanoven\u00ed kalibra\u010dn\u00edho koeficientu, kter\u00fd byl n\u00e1sledn\u011b pou\u017eit pro v\u00fdpo\u010det erozn\u00edch parametr\u016f. N\u00e1sledn\u011b bylo provedeno testov\u00e1n\u00ed p\u0159\u00edstroje, je\u017e prob\u00edhalo na experiment\u00e1ln\u00edch ploch\u00e1ch u\u00a0obce \u0158isuty (kambizem mod\u00e1ln\u00ed, prachovit\u00e1 hl\u00edna). Testov\u00e1n\u00ed prob\u00edhalo na dvou typech p\u016fdn\u00edch povrch\u016f (v\u00e1lcovan\u00fd \u00fahor, se\u0165ov\u00e9 lo\u017ee). Pomoc\u00ed metody \u201eScour depth\u201c byly vypo\u010dteny kritick\u00e9 te\u010dn\u00e9 nap\u011bt\u00ed a\u00a0koeficient erodovatelnosti.<\/p>\n

    Celkem bylo provedeno 75 simulac\u00ed, z toho 23 simulac\u00ed nebylo mo\u017eno z d\u016fvodu nerovnom\u011brn\u00e9ho pr\u016fb\u011bhu vyu\u017e\u00edt pro ur\u010den\u00ed erozn\u00edch parametr\u016f. \u00dasp\u011b\u0161nost v\u00fdpo\u010dtu erozn\u00edch parametr\u016f tak \u010dinila 69,3 %. Pro konsolidovan\u00fd p\u016fdn\u00ed povrch po p\u0159edchoz\u00edch sr\u00e1\u017ek\u00e1ch v \u00fahrnu 35 mm bylo oproti \u010derstv\u011b nakyp\u0159en\u00e9mu a v\u00e1lcovan\u00e9mu \u00fahoru nam\u011b\u0159eno \u010dty\u0159ikr\u00e1t vy\u0161\u0161\u00ed kritick\u00e9 te\u010dn\u00e9 nap\u011bt\u00ed (5,8 Pa oproti 1,4 Pa). To odpov\u00edd\u00e1 p\u0159ibli\u017en\u011b 6,5kr\u00e1t ni\u017e\u0161\u00edmu koeficientu erodovatelnosti. Z v\u00fdsledku je z\u0159ejm\u00e9, \u017ee konsolidace povrchu vlivem p\u0159edchoz\u00edch sr\u00e1\u017eek, vysych\u00e1n\u00ed a vznikaj\u00edc\u00ed p\u016fdn\u00ed krusta se v\u00fdrazn\u011b pod\u00edlej\u00ed na sn\u00ed\u017een\u00ed erodovatelnosti, tedy zv\u00fd\u0161en\u00ed odolnosti p\u016fdy proti dal\u0161\u00edmu rozru\u0161ov\u00e1n\u00ed erozn\u011b \u00fa\u010dinnou sr\u00e1\u017ekou. \u010cerstv\u011b p\u0159ipraven\u00fd \u00fahor a relativn\u011b such\u00fd povrch ihned po zaset\u00ed (po\u010d\u00e1te\u010dn\u00ed objemov\u00e1 vlhkost 19 %) je p\u0159i identick\u00fdch podm\u00ednk\u00e1ch v\u00edce n\u00e1chyln\u00fd k erozi ne\u017e konsolidovan\u00fd povrch s m\u011bs\u00ed\u010dn\u00edm odstupem po kultivaci a s vy\u0161\u0161\u00ed objemovou vlhkost\u00ed. Vztah ostatn\u00edch parametr\u016f k erodovatelnosti se prozat\u00edm nepoda\u0159ilo experimentem prok\u00e1zat.<\/p>\n

    V\u00fdrazn\u00e1 variabilita nam\u011b\u0159en\u00fdch v\u00fdsledk\u016f (sm\u011brodatn\u00e1 odchylka v\u00a0\u0159\u00e1du nam\u011b\u0159en\u00fdch hodnot erodovatelnosti) je u\u00a0podobn\u00fdch experiment\u016f b\u011b\u017en\u00e1, upozor\u0148uje v\u0161ak na v\u00fdznamnou nejistotu jednoho konkr\u00e9tn\u00edho m\u011b\u0159en\u00ed, proto je t\u0159eba v\u017edy prov\u00e9st dostate\u010dn\u00fd po\u010det experiment\u016f pro ur\u010den\u00ed pr\u016fkazn\u00fdch v\u00fdsledk\u016f. I\u00a0z\u00a0toho d\u016fvodu byly rovn\u011b\u017e pops\u00e1ny mo\u017en\u00e9 nejistoty a\u00a0chyby, jich\u017e se m\u016f\u017ee u\u017eivatel t\u00e9to metody dopustit. V\u00a0dal\u0161\u00edch experimentech bude c\u00edlem rovn\u011b\u017e minimalizace mo\u017en\u00fdch metodick\u00fdch chyb. Z\u00a0vypo\u010dten\u00fdch v\u00fdsledk\u016f erozn\u00edch parametr\u016f, kter\u00e9 byly porovn\u00e1ny se zahrani\u010dn\u00edmi studiemi proveden\u00fdmi na soudr\u017en\u011bj\u0161\u00edch p\u016fd\u00e1ch, vyplynulo, \u017ee za\u0159\u00edzen\u00ed pou\u017eit\u00e9 v\u00a0t\u00e9to studii lze pou\u017e\u00edt pro m\u011b\u0159en\u00ed kritick\u00e9ho te\u010dn\u00e9ho nap\u011bt\u00ed i\u00a0na nesoudr\u017en\u00fdch p\u016fd\u00e1ch, jak\u00fdmi jsou charakterizov\u00e1ny nap\u0159\u00edklad zem\u011bd\u011blsk\u00e9 pozemky po p\u0159edse\u0165ov\u00e9 p\u0159\u00edprav\u011b a\u00a0v\u00a0pr\u016fb\u011bhu sezony.<\/p>\n

    Pod\u011bkov\u00e1n\u00ed<\/h3>\n

    Tato pr\u00e1ce byla podpo\u0159ena v\u00fdzkumn\u00fdmi projekty LTAUSA19019, QK1920224, QK1810341 a\u00a0SGS20\/156\/OHK1\/3T\/11.<\/em><\/p>\n

    P\u0159\u00edsp\u011bvek pro\u0161el lektorsk\u00fdm \u0159\u00edzen\u00edm.<\/strong><\/p>\n

     <\/p>\n","protected":false},"excerpt":{"rendered":"

    The article describes a method for determining the erodibility of incohesive agricultural soils by means of the critical shear stress measuring. The \u201cJet Erosion Test\u201d (JET) was used to determine the critical shear stress. The mea-\u2028surement was performed using a modified Mini-JET device. The device is very suitable for field measurements, because it is small, light, requires a relatively small amount of water, and can be operated by single person. The principle of measuring the critical shear stress of the soil is based on monitoring the rate of erosion crater formation by the action of a water jet of known kinetic energy. Based on the erosion crater development, the erosion parameters of the soil, such as the critical shear stress and the erodibility coefficient, can be calculated.<\/p>\n","protected":false},"author":8,"featured_media":12905,"comment_status":"closed","ping_status":"closed","sticky":false,"template":"","format":"standard","meta":{"_acf_changed":false,"footnotes":""},"categories":[2,86],"tags":[2570,2571,2572,2533],"coauthors":[2530,1730,692,693,2531],"class_list":["post-13215","post","type-post","status-publish","format-standard","has-post-thumbnail","hentry","category-from-the-world-of-water-management","category-hydraulics-hydrology-and-hydrogeology","tag-critical-shear-stress","tag-erodibility-coefficient","tag-incohesive-soil","tag-mini-jet"],"acf":[],"_links":{"self":[{"href":"https:\/\/www.vtei.cz\/en\/wp-json\/wp\/v2\/posts\/13215","targetHints":{"allow":["GET"]}}],"collection":[{"href":"https:\/\/www.vtei.cz\/en\/wp-json\/wp\/v2\/posts"}],"about":[{"href":"https:\/\/www.vtei.cz\/en\/wp-json\/wp\/v2\/types\/post"}],"author":[{"embeddable":true,"href":"https:\/\/www.vtei.cz\/en\/wp-json\/wp\/v2\/users\/8"}],"replies":[{"embeddable":true,"href":"https:\/\/www.vtei.cz\/en\/wp-json\/wp\/v2\/comments?post=13215"}],"version-history":[{"count":5,"href":"https:\/\/www.vtei.cz\/en\/wp-json\/wp\/v2\/posts\/13215\/revisions"}],"predecessor-version":[{"id":30634,"href":"https:\/\/www.vtei.cz\/en\/wp-json\/wp\/v2\/posts\/13215\/revisions\/30634"}],"wp:featuredmedia":[{"embeddable":true,"href":"https:\/\/www.vtei.cz\/en\/wp-json\/wp\/v2\/media\/12905"}],"wp:attachment":[{"href":"https:\/\/www.vtei.cz\/en\/wp-json\/wp\/v2\/media?parent=13215"}],"wp:term":[{"taxonomy":"category","embeddable":true,"href":"https:\/\/www.vtei.cz\/en\/wp-json\/wp\/v2\/categories?post=13215"},{"taxonomy":"post_tag","embeddable":true,"href":"https:\/\/www.vtei.cz\/en\/wp-json\/wp\/v2\/tags?post=13215"},{"taxonomy":"author","embeddable":true,"href":"https:\/\/www.vtei.cz\/en\/wp-json\/wp\/v2\/coauthors?post=13215"}],"curies":[{"name":"wp","href":"https:\/\/api.w.org\/{rel}","templated":true}]}}