LNWB Ch07 Water Management - Agricultural water use - data

Overview:
Agricultural water use includes the irrigation of croplands and the water needs of dairy farms. Irrigated agriculture is an important component of the Lower Nooksack Water Budget due to the high demand for water during the relatively dry summer seasons. Along with out-of-basin industrial water use, irrigation is the largest use of water in the Lower Nooksack Subbasin and has a commensurate effect on the water budget. The highest demand for irrigation water occurs during the month of July when streamflows are low. Dairy water use equals the amount of water the cows drink plus the water used for washdown. The dairy demand is small relative to irrigation.

Since measured diversion or withdrawal records are not available, an estimate of crop irrigation requirements was developed using an empirically derived calculation of water demand. Drainage-wide irrigation estimates are based on the acres irrigated, type of crop, method of irrigation, and soil types.

Recent crop data from Washington Department of Agriculture and previous studies are summarized by surface water drainage area. The U.S. portion of the Lower Nooksack Subbasin contains approximately 54,044 acres of which 28,140 acres are irrigated or approximately 80% of the countywide irrigation total. Major crops include grass hay, pastureland, field corn, raspberries, and potatoes which comprise 97% of the crops grown in the Subbasin.

Within the 16 Lower Nooksack Subbasin drainages, the irrigated agriculture areas have the highest percent of total drainage area in Scott, Fourmile, Kamm, and Wiser Lake/Cougar Creek. Bertrand and Fishtrap Creek percentages include the irrigated area on both the US and Canadian sides. By volume alone, Bertrand and Fishtrap Creek drainages use the highest amount of irrigation water. Irrigation water use rates for each drainage can be found in Chapter 11 Existing Scenario, Water Budget Model Outputs for Lower Nooksack Drainages.

Crop evapotranspiration is an integral component of the hydrologic cycle and is calculated internally in the Topnet Water Management (Topnet-WM) model. The Topnet model uses the Penman Monteith method (adopted and standardized by the American Society of Civil Engineers (2005)) for calculating evapotranspiration of a reference crop [ETr] (short cut grass or tall alfalfa). Tall alfalfa is the reference crop integrated in the WRIA 1 Topnet model. The difference between potential and actual evapotranspiration is the amount of crop water demand that must be satisfied by irrigation.

Purpose:
This section defines the model inputs necessary for calculating the irrigation demand outputs. Results summarizing the irrigation demand on a monthly basis can be found in Chapter 11 Existing Conditions, Water Budget Model Outputs for Lower Nooksack Drainages.

Crop evapotranspiration is an integral component of the hydrologic cycle and is calculated, along with the other components of the water budget. The inputs defined in this chapter include crop type, number of acres, monthly crop coefficients, type of irrigation application (drip or spray) and irrigation efficiencies. Inputs were developed for the 16 Lower Nooksack Subbasin drainages only.

This resource is a subset of the LNWB Ch07 Water Management - Agricultural water use Collection Resource.

概述：
农业用水涵盖作物灌溉及乳牛场的用水需求。灌溉农业由于在相对干旱的夏季季节对水资源的高需求，是诺克斯纳克下游水预算的重要组成部分。灌溉与流域外工业用水共同构成了诺克斯纳克下游子流域最大的用水需求，并对水预算产生相应影响。灌溉用水需求在七月份达到最高，此时河流流量最低。乳牛用水需求等于奶牛饮水量与冲洗用水量之和。与灌溉用水相比，乳牛用水需求较小。
由于缺乏测量的分流或提水记录，因此通过经验推导的水需求计算方法开发了作物灌溉需求估算。流域范围内的灌溉估算基于灌溉面积、作物类型、灌溉方法和土壤类型。
通过华盛顿州农业部的最新作物数据和以往研究，对地表水排水区域进行了总结。诺克斯纳克下游子流域的美国部分大约有54,044英亩，其中28,140英亩用于灌溉，约占全县灌溉总面积的80%。主要作物包括牧草、牧场、玉米地、树莓和土豆，这些作物占子流域种植作物的97%。
在诺克斯纳克下游子流域的16个排水区域中，灌溉农业面积占总排水面积最高的是斯科特、四英里、卡姆和怀瑟湖/ Cougar Creek。贝特朗和Fishtrap Creek的百分比包括美国和加拿大两边的灌溉区域。仅从体积来看，贝特朗和Fishtrap Creek排水区域使用的水量最多。各排水区域的灌溉用水率可在第11章“现有情景，诺克斯纳克排水区域水预算模型输出”中找到。
作物蒸散量是水文循环的一个基本组成部分，并在Topnet水管理（Topnet-WM）模型内部计算。Topnet模型采用美国土木工程师学会（2005年）采纳和标准化的彭曼蒙特伊方法来计算参考作物（如短草或高苜蓿）的蒸散量[ETr]。在WRIA 1 Topnet模型中，高苜蓿是集成的参考作物。潜在蒸散量与实际蒸散量之间的差异即为必须通过灌溉满足的作物水分需求。
目的：
本节定义了计算灌溉需求输出的模型输入。有关按月总结的灌溉需求结果，可在第11章“现有条件，诺克斯纳克排水区域水预算模型输出”中找到。
作物蒸散量是水文循环的一个基本组成部分，并与其他水预算组成部分一起计算。本章定义的输入包括作物类型、面积、月度作物系数、灌溉应用类型（滴灌或喷灌）和灌溉效率。仅针对诺克斯纳克下游子流域的16个排水区域开发了输入。
本资源是LNWB Ch07水资源管理-农业用水收集资源的一个子集。