Periodic fluctuations in natural streamflow are a major driver of river ecosystem dynamics and water resource management. However, most U.S. rivers are impacted both by long-term hydroclimatic trends and dams that alter flow variability. Despite these impacts, it remains largely unexplored how dams affect the dominant frequencies of natural streamflow over a highly regulated river network. We investigated the entire Colorado River Basin (CRB) to understand how the annual (10–14 months) and multi-annual (24–60 months) frequencies in natural flow regimes have been progressively altered by dams. Given the significant alteration over the CRB, we captured changes in streamflow frequencies between naturalized and observed monthly flows via wavelet analysis. Based on the similarity of changes in streamflow frequencies (annual and multi-annual) over the last 30 years, sections of the riverine network were classified into four groups. The annual frequency was relatively well preserved downstream of Hoover Dam, while showing a systematic trend of alteration downstream of Glen Canyon Dam until Hoover Dam. Meanwhile, the multi-annual frequency component was highly altered for the entire Lower Colorado main stem (i.e., downstream of Glen Canyon). We also identified dams with significant impacts on streamflow frequency by comparing wavelet coherence estimates. This study advances the notion that dams fundamentally alter river flow regimes across multiple frequencies and with varying amplitudes over time and space, with alteration propagating – or being dampened – by both hydroclimatic fluctuations and water resource management.

中文翻译：

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量化大坝引起的科罗拉多河流域水流频率波动

自然流量的周期性波动是河流生态系统动态和水资源管理的主要驱动因素。然而，大多数美国河流都受到长期水文气候趋势和改变流量变化的大坝的影响。尽管有这些影响，但在高度管制的河网中，大坝如何影响自然水流的主要频率，在很大程度上仍未得到探索。我们调查了整个科罗拉多河流域 (CRB)，以了解大坝是如何逐渐改变自然流态中的年度（10-14 个月）和多年（24-60 个月）频率的。鉴于 CRB 的显着变化，我们通过小波分析捕获了自然月流量和观测月流量之间的流量频率变化。根据过去 30 年河流流量频率（年度和多年）变化的相似性，河流网络的部分被分为四组。年频率在胡佛水坝下游保存相对较好，同时在格伦峡谷水坝下游至胡佛水坝呈现系统性变化趋势。同时，整个下科罗拉多主干（即格伦峡谷下游）的多年频率分量发生了很大变化。我们还通过比较小波相干估计确定了对水流频率有重大影响的大坝。这项研究提出了这样一种观点，即大坝从根本上改变了多个频率的河流流态，并且随着时间和空间的变化幅度不同，