Idaho Code § 42-2946
In case of the establishment of a drainage district and system of drainage under the provisions of this chapter above any other district that may theretofore have been established, and above any other system of drainage that may have theretofore been constructed in said district, and in case said district to be established above may desire to connect its drainage system with the lower or servient district, the latter district shall be made a party to the proceedings for the establishment of such system, and the petition to be filed in the district court for the establishment of the system of drainage in said upper district shall in addition to the facts hereinbefore provided and required to be set forth therein, set forth the fact that said lower system in said lower district is necessary to be used as an outlet for the system of drainage of said upper district, and that the same will be sufficient outlet and will afford sufficient capacity to carry the drainage of both said upper and lower districts; and in case said system of said lower district will be required to be enlarged by widening or deepening the same, or both, in order to give sufficient outlet to said upper district and afford sufficient drainage for said upper and lower districts, then the plans and specifications for enlarging the system of said lower district shall be filed with said petition in addition to the other data hereinbefore provided for in this chapter.
All the landowners in said lower district, or any person claiming interest therein as mortgagee or otherwise, shall be made parties defendant in said petition, and the proceedings therein as to the assessment of damages and compensation for land taken, if any be necessary to be taken in enlarging said lower system, shall be the same as in the establishment of systems of drainage in the lower or servient district as hereinbefore provided for; but the jury, in addition to the facts to be found by them as provided for in the establishment of a drainage system in the lower district, shall find and determine whether said lower system, when improved according to the plans and specifications filed with the said petition, will afford sufficient drainage for both said upper and lower districts, which finding shall be made by the jury before considering any other question at issue in said proceedings, and in case said jury should find that the system of said lower district when improved as proposed in said petition would not be sufficient, then in that case said findings shall terminate the proceedings, and no further proceedings in said case shall be had, and the costs of said proceedings shall be paid as costs in other proceedings, as hereinbefore provided for; but in such case the finding of said jury shall not terminate the objects of said upper district or operate to disorganize the same, but said upper district may begin new proceedings for the establishment of a system of drainage with some new outlet provided therein.
All costs for the enlarging or improving of said lower system that may be required, shall be assessed to the landowners in the upper district according to the benefits to be derived from the construction of said entire system, and no additional cost shall be thrown upon the lower district, and all compensation for taking any right of way that may be necessary to be taken in enlarging said lower system and all damages occurring therefrom, if any, to the landowners of said lower district, shall be ascertained and paid in the same manner as hereinbefore provided for the adjustment of compensation and damages in the establishment of drainage systems in lower districts.
Said lower district, by and through its board of commissioners, may appear in said cause and show therein any injury it may sustain as a district by reason of the additional cost of maintenance per annum which will be sustained by said lower district by reason of said enlarging or improving of the same, and judgment shall be rendered in favor of said lower district against said upper district for such an amount as found, and the same shall be paid each year as the cost of construction is paid as provided for in this chapter, and the amount so paid shall be held by said lower district as an additional fund for the maintenance of its said system as improved and enlarged by said upper district.
Idaho Code § 42-2946